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  2. 12z Euro and CMC are the exact opposite of each other for day 10.
  3. A REVIEW OF ARCTIC AMPLIFICATION AND LOW ICE EXTENT IMPACTS ON NORTHERN HEMISPHERE CIRCULATION PATTERNS AND TEMPERATURE In recent years there has been a great deal of research into the impacts of the changing Arctic ice profile and how this influences the Northern Hemisphere now and going forward. I have read a number of excellent papers on this topic and placed a few of them into the Research Portal with many more to be added in the coming weeks and months. I shall review the last two entries in this post. Before that, as some of you already know, I take a very balanced view on Climate Change. I feel that there are too extremists at both ends of the debate and some papers are skewed or even use dubious data to support their biased views. This makes it much harder to try and understand the actual facts and to analyse what is really going on. Even when one is satisfied with the source and authenticity of what is presented, there are some highly conflicting conclusions. I am not going to attempt to come to any specific conclusions myself as I wish to keep an open mind and I realise that there is so much more research required. As many of the experts cannot agree on much of this, I do not believe that anyone can seriously be persuaded one way or the other - but these two papers may change a few minds! In any event, I want to provoke an ongoing debate on this forum as the potential impacts (or lack of them) have ramifications on broader global patterns and the interaction with other teleconnections and very much on medium, seasonal and long range forecasts. Last year I did a post on how low ice extent appeared to impact on changes on the strength, direction and position of the jet stream and I reviewed a couple of excellent papers back then - well things have moved on apace since then! I see that a number of members have already looked at these two papers in the portal, so they are definitely provoking some interest. I decided to place this post on the Arctic thread as we can generate a long term discussion here. The topic is just as relevant to the Teleconnections thread and the 2019-20 Winter Seasonal Discussion thread. I shall copy it on to both of those threads too and also on to the new UK and European Discussion thread. . Paper 1: Impact of Arctic sea ice variations on winter temperature anomalies in northern hemispheric land areas - Published 30th July, 2018 Link to portal entry Abstract: Coordinated numerical ensemble experiments with six different state-of-the-art atmosphere models have been used in order to evaluate the respective impact of the observed Arctic sea ice and sea surface temperature (SST) variations on air temperature variations in mid and high latitude land areas. Two sets of experiments have been designed; in the first set (EXP1), observed daily sea ice concentration and SST variations are used as lower boundary forcing over 1982–2014 while in the second set (EXP2) the SST variations are replaced by the daily SST climatology. The observed winter 2 m air temperature (T2m) variations are relatively well reproduced in a number of mid and high latitude land areas in EXP1, with best agreement in southwestern North America and northern Europe. Sea ice variations are important for the interannual T2m variations in northern Europe but have limited impact on all other mid and high latitude land regions. In particular, sea ice variations do not contribute to the observed opposite variations in the Arctic and mid latitude in our model experiments. The spread across ensemble members is large and many ensemble members are required to reproduce the observed T2m variations over northern Europe in our models. The amplitude of T2m anomalies in the coldest observed winters over northern Europe is not reproduced by our multi-model ensemble means. However, the sea ice conditions in these respective winters and mainly the thermodynamic response to the ice anomalies lead to an enhanced likelihood for occurrence of colder than normal winters and extremely cold winters. Still, the main reason for the observed extreme cold winters is internal atmospheric dynamics. The coldest simulated northern European winters in EXP1 and EXP2 between 1982 and 2014 show the same large scale T2m and atmospheric circulation anomaly patterns as the observed coldest winters, indicating that the models are well able to reproduce the processes, which cause these cold anomalies. The results are robust across all six models used in this study. Link to full paper: https://link.springer.com/content/pdf/10.1007%2Fs00382-018-4305-1.pdf My Review: The introduction goes though some of the rapid changes in Arctic temps during the last decade and correctly stating that the mean temps in the wider Arctic region have risen by more than 2c since 1850 which is 2 to 3 times faster than the rise in global temps. Some of the known causes of this are stated with reference to a number of other papers. Temperature feedback loops are mentioned as well as the extreme variations in snow cover in the surrounding land masses - another subject that I've posted on frequently and will not repeat now accept to say that the snow cover itself is (or was) believed to have influences on the atmosphere (eg: Judah Cohen's correlation theory with early season/October snow extent in Eurasia and Siberia and its impact on potential SSWs and minor warmings). Then the rapid decline in overall Arctic ice extent is outlined - something which many of the posts on the Arctic thread refer to. Reference is made to the distribution of temperatures and heat fluxes and the greatest warming, usually near the ice edge periphery such as around the Barents Sea. Then the more controversial theory (which is getting a lot of exposure right now) that low sea ice extent in late Summer and in the Autumn (Fall) is linked to a -ve NAO the following Winter. (The jury is still out on this one!). There is reference to theories that low sea ice in the Barents and Kara Seas has been associated with strong impacts on lower latitudes. They refer to moisture fluxes from the Arctic to Eurasia coupled with low Arctic ice and greater land mass snow cover there, has an impact on the northern hemisphere circulation and on the atmosphere above. The main changes are theories that the decline in ice extent since 2000 is related to a greater frequency and more extreme cold conditions in central Eurasia and North America. These and further theories on perceived impacts are mentioned. The authors do emphasise that the time period for all these changes and potential impacts is very short (this is where I feel that particular caution is required). They also state, "the climate system is complex and many variables have changed over the last years, which makes it uncertain if the sea ice really is the main driver for mid-latitude climate events". They say that some of the changes may be more influenced by changes in the Atlantic and the Pacific (such as changes in SST anomalies). The authors state how they tested some of these theories - they say "this present study uses by far largest number of models for coordinated sensitivity experiments. We use these large ensemble simulations to investigate the effect of sea ice variations on climate variations in mid and high latitude land areas." They go through what they investigated and the model experiments and data employed. I will now jump to the results and quote part of that. " The experiments show that Arctic sea ice variations largely capture the observed decadal variations in winter Arctic temperature, but not those in mid-latitudes"...." the warm Arctic temperature anomalies after 2005 extend into the mid-latitudes in EXP1. EXP2 shows generally small mid-latitude T2m anomalies, indicating little impact of the sea ice variations on zonally averaged mid-latitude temperature anomalies". For North America the experiment shows or reconfirms that "the SST-forcing seems to be the main driver of winter temperature variations, which is consistent with the dominant teleconnection from the tropical Pacific region. The El Niño Southern Oscillation is known to drive the Pacific North American Pattern in winter, which has a dominant impact on the winter climate over North America." " SST is the main driver for interannual variation. Thus, using climatological SST boundary conditions is not reducing the internal variability in EXP2 as one might expect." The experiments did suggest some correlation In respect of colder Northern European Winters and this became more of the focus: "In the following, we focus on the coldest observed winters in N Europe; we selected those winters from the detrended ERA-interim data, which exceed an anomaly of − 1.5 standard deviations (which means T2m anomalies exceeding −3 K). Based on this criterion, the four winters 1984/1985 (DJF 1985), 1986/1987 (DJF 1987), 2009/2010 (DJF 2010) and 2010/2011 (DJF 2011) are selected. These winters were also some of the coldest winters over Central and Eastern Europe and larger parts of Asia and have in common that anomalously easterly or northeasterly winds advect cold air to N Europe, as seen in the ERA-interim data (Figs. 6, 7). These winds are related to a pronounced NAO-like pattern with positive SLP anomalies over the Nordic Seas and the Arctic and negative SLP anomalies over the North Atlantic that are associated with anticy - clonic anomalies from Scandinavia to the Ural Mountains, and low pressure anomalies south of it. DJF 1987 and DJF 2011 show at the same time a negative SLP-anomaly over the Aleutian Islands, while in DJF 1985 and DJF 2010, positive SLP anomalies occur in the North Pacific; these are consistent with ENSO teleconnection (Di Lorenzo et al. 2010), as weak to moderate El Niño conditions are observed in 1987 and 2010, and La Niña conditions in 1985 and 2011. There is a lot more on this with numerous charts. There is also more reference to the North Atlantic and Pacific. The conclusions - after referring to the shortcomings, they say: "our model experiments reveal robust results across our six atmosphere models. The correlation between winter T2m variations in EXP1 and ERA-interim data is high for all ocean areas but lower over land. However, the T2m average over most of ten different mid and high latitude continental sub domains is significantly correlated with the ERA-interim data. In contrast, T2m in EXP2 is only significantly correlated with ERAinterim over the Arctic Ocean, in northern Europe and northeastern North America. This indicates that sea ice variations have only a limited impact on T2m variations in most mid and high northern latitude regions. Further, the suggested warm Arctic—cold continent pattern (Overland et al. 2011). is only partly reproduced in EXP1 and not reproduced in EXP2 as a response to lower boundary and radiative forcing. Thus, according to our experiments this pattern is unlikely to be due to sea ice variations in reality and might represent internal atmospheric circulation variability. The ice variations are important for the interannual variations of winter T2m in N Europe although the amplitude of the anomalies in the multi-model ensemble mean is about three times smaller than in ERA-interim. This is mainly due to a large spread of simulated T2m-anomalies across the individual ensemble members and shows that many ensemble members are needed to simulate the observed T2m variations over N Europe. November sea ice anomalies in the Beaufort Sea seems to play an important role for the T2m in N Europe in the following winter. They are highly negatively correlated with winter sea ice in the Barents Sea. Those in turn contribute thermodynamically to T2m anomalies in N Europe. Our results revealed a robust response of the ice impact on N Europe T2m across the individual model ensemble means. The T2m in N Europe of each single model ensemble mean is significantly correlated with ERA-interim. However, as for the multi-model ensemble mean, the amplitude of the single model ensemble mean T2m responses are about three times weaker than the observed anomalies (Fig. 2). Such characteristics of the ensemble response may be related to the forced one-way interaction in our AGCM simulations, when the simulated ensemble mean response represents a feedback from the SST and sea ice anomalies originally caused by internal atmosphere variability (Bretherton and Battisti 2000). However, it could also suggest a too weak atmospheric response to surface forcing (Eade et al. 2014). The sea ice conditions in the four coldest observed winters (exceeding cold anomalies of 1.5 standard deviations) in ERA-interim in N Europe since 1982, increase the probability for cold winters in N Europe in the models. However, only few ensemble members simulate T2m anomalies that are as large as the observed ones in these winters. Further, we found that T2m and SLP amplitudes and patterns in the coldest simulated winters in N Europe (which can differ from the observed winters) in the models since 1982 agree well with the coldest winters in ERA-interim. This shows that the models are able to realistically reproduce large-scale circulation and T2m anomaly patterns during extremely cold winters in N Europe. Thus, the fact that the models do not fully reproduce the observed cold winters in these specific winters is not caused by a general failure of the models to reproduce large scale conditions and processes that cause cold winters in N Europe. Therefore, we conclude, that the occurrence of the observed extremely cold winters in these specific years is mainly due to natural variations of the atmospheric circulation and only to a smaller part caused by the underlying sea ice and SST conditions. The results from our study, in contrast to those studies, which suggested a clear link between sea ice and mid latitude cold winters, do not reveal a robust sea ice impact. Our results suggest instead the major role of internal variability for the recent climate anomalies in lower latitudes. When I first skimmed through this paper a few months ago, I felt that their experiments were confirming the relationship between low sea ice extent and northern hemisphere temperatures. Although there is some correlation between regional low sea ice and Eurasian and North European Winters, the experiments and the authors' conclusion relate this to various other factors as well. I feel that we need more years to provide further evidence but logically, as low sea ice extent has been present in almost all the last 10 winters and indeed back to the early 2000s, then one might expect there to be more consistent and frequent impacts. Of course, the interaction of low sea ice extent and a warmer Arctic with other teleconnections needs to be thoroughly investigated. In some seasons/years certain teleconnections might be more dominant but in other years different ones might be. So, without completely dismissing the more direct correlations and theories, this paper does come to rather different conclusions to many previous papers earlier in the decade and up to late 2017. The next paper goes a lot further! Paper 2: Minimal influence of reduced Arctic sea ice on coincident cold winters in mid-latitudes - Published 12th August, 2019 Link to portal entry Abstract: Observations show that reduced regional sea-ice cover is coincident with cold mid-latitude winters on interannual timescales. However, it remains unclear whether these observed links are causal, and model experiments suggest that they might not be. Here we apply two independent approaches to infer causality from observations and climate models and to reconcile these sources of data. Models capture the observed correlations between reduced sea ice and cold mid-latitude winters, but only when reduced sea ice coincides with anomalous heat transfer from the atmosphere to the ocean, implying that the atmosphere is driving the loss. Causal inference from the physics-based approach is corroborated by a lead–lag analysis, showing that circulation-driven temperature anomalies precede, but do not follow, reduced sea ice. Furthermore, no mid-latitude cooling is found in modelling experiments with imposed future sea-ice loss. Our results show robust support for anomalous atmospheric circulation simultaneously driving cold mid-latitude winters and mild Arctic conditions, and reduced sea ice having a minimal influence on severe mid-latitude winters. Link to full paper: Unfortunately this fascinating very recent paper is still behind the "Nature Climate Change" paywall. I'm not a subscriber but if anyone is, then here's the link: https://www.nature.com/articles/s41558-019-0551-4 If/when the paper becomes freely available, the link will appear here. In the meantime, if anyone does have a link (with permissions), please PM me or "reply to topic" below. Then I can add the link sooner and I can give you credit for finding the paper. I did find several articles about this paper which provide a little more detail: https://phys.org/news/2019-08-arctic-sea-ice-loss-minimal-severe.html It is a shame that this very recent paper is behind a paywall. The article that I provide a link to is worth repeating in full here: "Arctic sea-ice loss has 'minimal influence' on severe cold winter weather, research shows - by University of Exeter The dramatic loss of Arctic sea ice through climate change has only a "minimal influence" on severe cold winter weather across Asia and North America, new research has shown. The possible connection between Arctic sea-ice loss and extreme cold weather—such as the deep freezes that can grip the USA in the winter months—has long been studied by scientists. Observations show that when the regional sea-ice cover is reduced, swathes of Asia and North America often experience unusually cold and hazardous winter conditions. However, previous climate modelling studies have suggested that reduced sea ice cannot fully explain the cold winters. Now, a new study by experts from the University of Exeter, the Royal Netherlands Meteorological Institute and the Energy and Sustainability Research Institute in Groningen, has shed new light on the link between sea-ice loss and cold winters. For the research, the international team combined observations over the past 40 years with results from sophisticated climate modelling experiments. They found that the observations and models agreed that reduced regional sea ice and cold winters often coincide which each other. They found that the correlation between reduced sea ice and extreme winters across the mid-latitude occurs because both are simultaneously driven by the same, large-scale atmospheric circulation patterns. Crucially, it shows that reduced sea ice only has a minimal influence on whether a harsh and severe winter will occur. The study is published in leading science journal, Nature Climate Change. Dr. Russell Blackport, a Mathematics Research Fellow at the University of Exeter and lead author of the paper said: "The correlation between reduced sea ice and cold winters does not mean one is causing the other. We show that the real cause is changes in atmospheric circulation which moves warm air into the Arctic and cold air into the mid-latitudes." Over recent decades, the Arctic region has experienced warming temperatures through climate change, which has led to a large decline in sea-ice cover. This reduction in sea-ice cover means that areas of open water increase, which in turn allows the ocean to lose more heat to the atmosphere in winter—this can potentially alter the weather and climate, even well outside the Arctic. Recent studies have suggested that the reduced sea ice or Arctic warming has contributed to recent cold winters experienced in the mid-latitude region—and that as the sea-ice reduces further through climate change, cold winters will become more frequent and severe. Now, this new study suggests that reduced sea ice is not the main cause of the cold winters. Instead, the cold winters are likely caused by random fluctuations in the atmospheric circulation. Professor James Screen, an Associate Professor in Climate Science at the University of Exeter said: "The are many reasons to be concerned about the dramatic loss of Arctic sea ice, but an increased risk of severe winters in North America and Asia is not one of them." Dr. John Fyfe, a Research Scientist at the Canadian Centre for Climate Modelling and Analysis, who was not involved in the research, writes in Nature Climate Change: "Blackport and colleagues put to rest the notion that Arctic sea-ice loss caused the cold mid-latitude winters, showing instead that atmospheric circulation changes preceded, and then simultaneously drove sea-ice loss and mid-latitude cooling". So this paper shows that many of the factors that are changing the Arctic climate are also changing large scale atmospheric circulation and mid latitude climate patterns and the correlations and "cause and effect" relationships are much weaker than many earlier studies have suggested. Obviously we need to see further research supporting (or rejecting) the conclusions of this paper. What I feel that we all need to do is perhaps to "think outside of the box" - assess the macro influences and then how these all interact. In many ways this is what the study of Teleconnections is all about. Arctic sea ice extent and amplification/warming are just two of many. David
  4. A REVIEW OF ARCTIC AMPLIFICATION AND LOW ICE EXTENT IMPACTS ON NORTHERN HEMISPHERE CIRCULATION PATTERNS AND TEMPERATURE In recent years there has been a great deal of research into the impacts of the changing Arctic ice profile and how this influences the Northern Hemisphere now and going forward. I have read a number of excellent papers on this topic and placed a few of them into the Research Portal with many more to be added in the coming weeks and months. I shall review the last two entries in this post. Before that, as some of you already know, I take a very balanced view on Climate Change. I feel that there are too extremists at both ends of the debate and some papers are skewed or even use dubious data to support their biased views. This makes it much harder to try and understand the actual facts and to analyse what is really going on. Even when one is satisfied with the source and authenticity of what is presented, there are some highly conflicting conclusions. I am not going to attempt to come to any specific conclusions myself as I wish to keep an open mind and I realise that there is so much more research required. As many of the experts cannot agree on much of this, I do not believe that anyone can seriously be persuaded one way or the other - but these two papers may change a few minds! In any event, I want to provoke an ongoing debate on this forum as the potential impacts (or lack of them) have ramifications on broader global patterns and the interaction with other teleconnections and very much on medium, seasonal and long range forecasts. Last year I did a post on how low ice extent appeared to impact on changes on the strength, direction and position of the jet stream and I reviewed a couple of excellent papers back then - well things have moved on apace since then! I see that a number of members have already looked at these two papers in the portal, so they are definitely provoking some interest. I decided to place this post on the Arctic thread as we can generate a long term discussion here. The topic is just as relevant to the Teleconnections thread and the 2019-20 Winter Seasonal Discussion thread. I shall copy it on to both of those threads too and also on to the new UK and European Discussion thread. . Paper 1: Impact of Arctic sea ice variations on winter temperature anomalies in northern hemispheric land areas - Published 30th July, 2018 Link to portal entry Abstract: Coordinated numerical ensemble experiments with six different state-of-the-art atmosphere models have been used in order to evaluate the respective impact of the observed Arctic sea ice and sea surface temperature (SST) variations on air temperature variations in mid and high latitude land areas. Two sets of experiments have been designed; in the first set (EXP1), observed daily sea ice concentration and SST variations are used as lower boundary forcing over 1982–2014 while in the second set (EXP2) the SST variations are replaced by the daily SST climatology. The observed winter 2 m air temperature (T2m) variations are relatively well reproduced in a number of mid and high latitude land areas in EXP1, with best agreement in southwestern North America and northern Europe. Sea ice variations are important for the interannual T2m variations in northern Europe but have limited impact on all other mid and high latitude land regions. In particular, sea ice variations do not contribute to the observed opposite variations in the Arctic and mid latitude in our model experiments. The spread across ensemble members is large and many ensemble members are required to reproduce the observed T2m variations over northern Europe in our models. The amplitude of T2m anomalies in the coldest observed winters over northern Europe is not reproduced by our multi-model ensemble means. However, the sea ice conditions in these respective winters and mainly the thermodynamic response to the ice anomalies lead to an enhanced likelihood for occurrence of colder than normal winters and extremely cold winters. Still, the main reason for the observed extreme cold winters is internal atmospheric dynamics. The coldest simulated northern European winters in EXP1 and EXP2 between 1982 and 2014 show the same large scale T2m and atmospheric circulation anomaly patterns as the observed coldest winters, indicating that the models are well able to reproduce the processes, which cause these cold anomalies. The results are robust across all six models used in this study. Link to full paper: https://link.springer.com/content/pdf/10.1007%2Fs00382-018-4305-1.pdf My Review: The introduction goes though some of the rapid changes in Arctic temps during the last decade and correctly stating that the mean temps in the wider Arctic region have risen by more than 2c since 1850 which is 2 to 3 times faster than the rise in global temps. Some of the known causes of this are stated with reference to a number of other papers. Temperature feedback loops are mentioned as well as the extreme variations in snow cover in the surrounding land masses - another subject that I've posted on frequently and will not repeat now accept to say that the snow cover itself is (or was) believed to have influences on the atmosphere (eg: Judah Cohen's correlation theory with early season/October snow extent in Eurasia and Siberia and its impact on potential SSWs and minor warmings). Then the rapid decline in overall Arctic ice extent is outlined - something which many of the posts on the Arctic thread refer to. Reference is made to the distribution of temperatures and heat fluxes and the greatest warming, usually near the ice edge periphery such as around the Barents Sea. Then the more controversial theory (which is getting a lot of exposure right now) that low sea ice extent in late Summer and in the Autumn (Fall) is linked to a -ve NAO the following Winter. (The jury is still out on this one!). There is reference to theories that low sea ice in the Barents and Kara Seas has been associated with strong impacts on lower latitudes. They refer to moisture fluxes from the Arctic to Eurasia coupled with low Arctic ice and greater land mass snow cover there, has an impact on the northern hemisphere circulation and on the atmosphere above. The main changes are theories that the decline in ice extent since 2000 is related to a greater frequency and more extreme cold conditions in central Eurasia and North America. These and further theories on perceived impacts are mentioned. The authors do emphasise that the time period for all these changes and potential impacts is very short (this is where I feel that particular caution is required). They also state, "the climate system is complex and many variables have changed over the last years, which makes it uncertain if the sea ice really is the main driver for mid-latitude climate events". They say that some of the changes may be more influenced by changes in the Atlantic and the Pacific (such as changes in SST anomalies). The authors state how they tested some of these theories - they say "this present study uses by far largest number of models for coordinated sensitivity experiments. We use these large ensemble simulations to investigate the effect of sea ice variations on climate variations in mid and high latitude land areas." They go through what they investigated and the model experiments and data employed. I will now jump to the results and quote part of that. " The experiments show that Arctic sea ice variations largely capture the observed decadal variations in winter Arctic temperature, but not those in mid-latitudes"...." the warm Arctic temperature anomalies after 2005 extend into the mid-latitudes in EXP1. EXP2 shows generally small mid-latitude T2m anomalies, indicating little impact of the sea ice variations on zonally averaged mid-latitude temperature anomalies". For North America the experiment shows or reconfirms that "the SST-forcing seems to be the main driver of winter temperature variations, which is consistent with the dominant teleconnection from the tropical Pacific region. The El Niño Southern Oscillation is known to drive the Pacific North American Pattern in winter, which has a dominant impact on the winter climate over North America." " SST is the main driver for interannual variation. Thus, using climatological SST boundary conditions is not reducing the internal variability in EXP2 as one might expect." The experiments did suggest some correlation In respect of colder Northern European Winters and this became more of the focus: "In the following, we focus on the coldest observed winters in N Europe; we selected those winters from the detrended ERA-interim data, which exceed an anomaly of − 1.5 standard deviations (which means T2m anomalies exceeding −3 K). Based on this criterion, the four winters 1984/1985 (DJF 1985), 1986/1987 (DJF 1987), 2009/2010 (DJF 2010) and 2010/2011 (DJF 2011) are selected. These winters were also some of the coldest winters over Central and Eastern Europe and larger parts of Asia and have in common that anomalously easterly or northeasterly winds advect cold air to N Europe, as seen in the ERA-interim data (Figs. 6, 7). These winds are related to a pronounced NAO-like pattern with positive SLP anomalies over the Nordic Seas and the Arctic and negative SLP anomalies over the North Atlantic that are associated with anticy - clonic anomalies from Scandinavia to the Ural Mountains, and low pressure anomalies south of it. DJF 1987 and DJF 2011 show at the same time a negative SLP-anomaly over the Aleutian Islands, while in DJF 1985 and DJF 2010, positive SLP anomalies occur in the North Pacific; these are consistent with ENSO teleconnection (Di Lorenzo et al. 2010), as weak to moderate El Niño conditions are observed in 1987 and 2010, and La Niña conditions in 1985 and 2011. There is a lot more on this with numerous charts. There is also more reference to the North Atlantic and Pacific. The conclusions - after referring to the shortcomings, they say: "our model experiments reveal robust results across our six atmosphere models. The correlation between winter T2m variations in EXP1 and ERA-interim data is high for all ocean areas but lower over land. However, the T2m average over most of ten different mid and high latitude continental sub domains is significantly correlated with the ERA-interim data. In contrast, T2m in EXP2 is only significantly correlated with ERAinterim over the Arctic Ocean, in northern Europe and northeastern North America. This indicates that sea ice variations have only a limited impact on T2m variations in most mid and high northern latitude regions. Further, the suggested warm Arctic—cold continent pattern (Overland et al. 2011). is only partly reproduced in EXP1 and not reproduced in EXP2 as a response to lower boundary and radiative forcing. Thus, according to our experiments this pattern is unlikely to be due to sea ice variations in reality and might represent internal atmospheric circulation variability. The ice variations are important for the interannual variations of winter T2m in N Europe although the amplitude of the anomalies in the multi-model ensemble mean is about three times smaller than in ERA-interim. This is mainly due to a large spread of simulated T2m-anomalies across the individual ensemble members and shows that many ensemble members are needed to simulate the observed T2m variations over N Europe. November sea ice anomalies in the Beaufort Sea seems to play an important role for the T2m in N Europe in the following winter. They are highly negatively correlated with winter sea ice in the Barents Sea. Those in turn contribute thermodynamically to T2m anomalies in N Europe. Our results revealed a robust response of the ice impact on N Europe T2m across the individual model ensemble means. The T2m in N Europe of each single model ensemble mean is significantly correlated with ERA-interim. However, as for the multi-model ensemble mean, the amplitude of the single model ensemble mean T2m responses are about three times weaker than the observed anomalies (Fig. 2). Such characteristics of the ensemble response may be related to the forced one-way interaction in our AGCM simulations, when the simulated ensemble mean response represents a feedback from the SST and sea ice anomalies originally caused by internal atmosphere variability (Bretherton and Battisti 2000). However, it could also suggest a too weak atmospheric response to surface forcing (Eade et al. 2014). The sea ice conditions in the four coldest observed winters (exceeding cold anomalies of 1.5 standard deviations) in ERA-interim in N Europe since 1982, increase the probability for cold winters in N Europe in the models. However, only few ensemble members simulate T2m anomalies that are as large as the observed ones in these winters. Further, we found that T2m and SLP amplitudes and patterns in the coldest simulated winters in N Europe (which can differ from the observed winters) in the models since 1982 agree well with the coldest winters in ERA-interim. This shows that the models are able to realistically reproduce large-scale circulation and T2m anomaly patterns during extremely cold winters in N Europe. Thus, the fact that the models do not fully reproduce the observed cold winters in these specific winters is not caused by a general failure of the models to reproduce large scale conditions and processes that cause cold winters in N Europe. Therefore, we conclude, that the occurrence of the observed extremely cold winters in these specific years is mainly due to natural variations of the atmospheric circulation and only to a smaller part caused by the underlying sea ice and SST conditions. The results from our study, in contrast to those studies, which suggested a clear link between sea ice and mid latitude cold winters, do not reveal a robust sea ice impact. Our results suggest instead the major role of internal variability for the recent climate anomalies in lower latitudes. When I first skimmed through this paper a few months ago, I felt that their experiments were confirming the relationship between low sea ice extent and northern hemisphere temperatures. Although there is some correlation between regional low sea ice and Eurasian and North European Winters, the experiments and the authors' conclusion relate this to various other factors as well. I feel that we need more years to provide further evidence but logically, as low sea ice extent has been present in almost all the last 10 winters and indeed back to the early 2000s, then one might expect there to be more consistent and frequent impacts. Of course, the interaction of low sea ice extent and a warmer Arctic with other teleconnections needs to be thoroughly investigated. In some seasons/years certain teleconnections might be more dominant but in other years different ones might be. So, without completely dismissing the more direct correlations and theories, this paper does come to rather different conclusions to many previous papers earlier in the decade and up to late 2017. The next paper goes a lot further! Paper 2: Minimal influence of reduced Arctic sea ice on coincident cold winters in mid-latitudes - Published 12th August, 2019 Link to portal entry Abstract: Observations show that reduced regional sea-ice cover is coincident with cold mid-latitude winters on interannual timescales. However, it remains unclear whether these observed links are causal, and model experiments suggest that they might not be. Here we apply two independent approaches to infer causality from observations and climate models and to reconcile these sources of data. Models capture the observed correlations between reduced sea ice and cold mid-latitude winters, but only when reduced sea ice coincides with anomalous heat transfer from the atmosphere to the ocean, implying that the atmosphere is driving the loss. Causal inference from the physics-based approach is corroborated by a lead–lag analysis, showing that circulation-driven temperature anomalies precede, but do not follow, reduced sea ice. Furthermore, no mid-latitude cooling is found in modelling experiments with imposed future sea-ice loss. Our results show robust support for anomalous atmospheric circulation simultaneously driving cold mid-latitude winters and mild Arctic conditions, and reduced sea ice having a minimal influence on severe mid-latitude winters. Link to full paper: Unfortunately this fascinating very recent paper is still behind the "Nature Climate Change" paywall. I'm not a subscriber but if anyone is, then here's the link: https://www.nature.com/articles/s41558-019-0551-4 If/when the paper becomes freely available, the link will appear here. In the meantime, if anyone does have a link (with permissions), please PM me or "reply to topic" below. Then I can add the link sooner and I can give you credit for finding the paper. I did find several articles about this paper which provide a little more detail: https://phys.org/news/2019-08-arctic-sea-ice-loss-minimal-severe.html It is a shame that this very recent paper is behind a paywall. The article that I provide a link to is worth repeating in full here: "Arctic sea-ice loss has 'minimal influence' on severe cold winter weather, research shows - by University of Exeter The dramatic loss of Arctic sea ice through climate change has only a "minimal influence" on severe cold winter weather across Asia and North America, new research has shown. The possible connection between Arctic sea-ice loss and extreme cold weather—such as the deep freezes that can grip the USA in the winter months—has long been studied by scientists. Observations show that when the regional sea-ice cover is reduced, swathes of Asia and North America often experience unusually cold and hazardous winter conditions. However, previous climate modelling studies have suggested that reduced sea ice cannot fully explain the cold winters. Now, a new study by experts from the University of Exeter, the Royal Netherlands Meteorological Institute and the Energy and Sustainability Research Institute in Groningen, has shed new light on the link between sea-ice loss and cold winters. For the research, the international team combined observations over the past 40 years with results from sophisticated climate modelling experiments. They found that the observations and models agreed that reduced regional sea ice and cold winters often coincide which each other. They found that the correlation between reduced sea ice and extreme winters across the mid-latitude occurs because both are simultaneously driven by the same, large-scale atmospheric circulation patterns. Crucially, it shows that reduced sea ice only has a minimal influence on whether a harsh and severe winter will occur. The study is published in leading science journal, Nature Climate Change. Dr. Russell Blackport, a Mathematics Research Fellow at the University of Exeter and lead author of the paper said: "The correlation between reduced sea ice and cold winters does not mean one is causing the other. We show that the real cause is changes in atmospheric circulation which moves warm air into the Arctic and cold air into the mid-latitudes." Over recent decades, the Arctic region has experienced warming temperatures through climate change, which has led to a large decline in sea-ice cover. This reduction in sea-ice cover means that areas of open water increase, which in turn allows the ocean to lose more heat to the atmosphere in winter—this can potentially alter the weather and climate, even well outside the Arctic. Recent studies have suggested that the reduced sea ice or Arctic warming has contributed to recent cold winters experienced in the mid-latitude region—and that as the sea-ice reduces further through climate change, cold winters will become more frequent and severe. Now, this new study suggests that reduced sea ice is not the main cause of the cold winters. Instead, the cold winters are likely caused by random fluctuations in the atmospheric circulation. Professor James Screen, an Associate Professor in Climate Science at the University of Exeter said: "The are many reasons to be concerned about the dramatic loss of Arctic sea ice, but an increased risk of severe winters in North America and Asia is not one of them." Dr. John Fyfe, a Research Scientist at the Canadian Centre for Climate Modelling and Analysis, who was not involved in the research, writes in Nature Climate Change: "Blackport and colleagues put to rest the notion that Arctic sea-ice loss caused the cold mid-latitude winters, showing instead that atmospheric circulation changes preceded, and then simultaneously drove sea-ice loss and mid-latitude cooling". So this paper shows that many of the factors that are changing the Arctic climate are also changing large scale atmospheric circulation and mid latitude climate patterns and the correlations and "cause and effect" relationships are much weaker than many earlier studies have suggested. Obviously we need to see further research supporting (or rejecting) the conclusions of this paper. What I feel that we all need to do is perhaps to "think outside of the box" - assess the macro influences and then how these all interact. In many ways this is what the study of Teleconnections is all about. Arctic sea ice extent and amplification/warming are just two of many. David
  5. A REVIEW OF ARCTIC AMPLIFICATION AND LOW ICE EXTENT IMPACTS ON NORTHERN HEMISPHERE CIRCULATION PATTERNS AND TEMPERATURE In recent years there has been a great deal of research into the impacts of the changing Arctic ice profile and how this influences the Northern Hemisphere now and going forward. I have read a number of excellent papers on this topic and placed a few of them into the Research Portal with many more to be added in the coming weeks and months. I shall review the last two entries in this post. Before that, as some of you already know, I take a very balanced view on Climate Change. I feel that there are too extremists at both ends of the debate and some papers are skewed or even use dubious data to support their biased views. This makes it much harder to try and understand the actual facts and to analyse what is really going on. Even when one is satisfied with the source and authenticity of what is presented, there are some highly conflicting conclusions. I am not going to attempt to come to any specific conclusions myself as I wish to keep an open mind and I realise that there is so much more research required. As many of the experts cannot agree on much of this, I do not believe that anyone can seriously be persuaded one way or the other - but these two papers may change a few minds! In any event, I want to provoke an ongoing debate on this forum as the potential impacts (or lack of them) have ramifications on broader global patterns and the interaction with other teleconnections and very much on medium, seasonal and long range forecasts. Last year I did a post on how low ice extent appeared to impact on changes on the strength, direction and position of the jet stream and I reviewed a couple of excellent papers back then - well things have moved on apace since then! I see that a number of members have already looked at these two papers in the portal, so they are definitely provoking some interest. I decided to place this post on the Arctic thread as we can generate a long term discussion here. The topic is just as relevant to the Teleconnections thread and the 2019-20 Winter Seasonal Discussion thread. I shall copy it on to both of those threads too and also on to the new UK and European Discussion thread. . Paper 1: Impact of Arctic sea ice variations on winter temperature anomalies in northern hemispheric land areas - Published 30th July, 2018 Link to portal entry Abstract: Coordinated numerical ensemble experiments with six different state-of-the-art atmosphere models have been used in order to evaluate the respective impact of the observed Arctic sea ice and sea surface temperature (SST) variations on air temperature variations in mid and high latitude land areas. Two sets of experiments have been designed; in the first set (EXP1), observed daily sea ice concentration and SST variations are used as lower boundary forcing over 1982–2014 while in the second set (EXP2) the SST variations are replaced by the daily SST climatology. The observed winter 2 m air temperature (T2m) variations are relatively well reproduced in a number of mid and high latitude land areas in EXP1, with best agreement in southwestern North America and northern Europe. Sea ice variations are important for the interannual T2m variations in northern Europe but have limited impact on all other mid and high latitude land regions. In particular, sea ice variations do not contribute to the observed opposite variations in the Arctic and mid latitude in our model experiments. The spread across ensemble members is large and many ensemble members are required to reproduce the observed T2m variations over northern Europe in our models. The amplitude of T2m anomalies in the coldest observed winters over northern Europe is not reproduced by our multi-model ensemble means. However, the sea ice conditions in these respective winters and mainly the thermodynamic response to the ice anomalies lead to an enhanced likelihood for occurrence of colder than normal winters and extremely cold winters. Still, the main reason for the observed extreme cold winters is internal atmospheric dynamics. The coldest simulated northern European winters in EXP1 and EXP2 between 1982 and 2014 show the same large scale T2m and atmospheric circulation anomaly patterns as the observed coldest winters, indicating that the models are well able to reproduce the processes, which cause these cold anomalies. The results are robust across all six models used in this study. Link to full paper: https://link.springer.com/content/pdf/10.1007%2Fs00382-018-4305-1.pdf My Review: The introduction goes though some of the rapid changes in Arctic temps during the last decade and correctly stating that the mean temps in the wider Arctic region have risen by more than 2c since 1850 which is 2 to 3 times faster than the rise in global temps. Some of the known causes of this are stated with reference to a number of other papers. Temperature feedback loops are mentioned as well as the extreme variations in snow cover in the surrounding land masses - another subject that I've posted on frequently and will not repeat now accept to say that the snow cover itself is (or was) believed to have influences on the atmosphere (eg: Judah Cohen's correlation theory with early season/October snow extent in Eurasia and Siberia and its impact on potential SSWs and minor warmings). Then the rapid decline in overall Arctic ice extent is outlined - something which many of the posts on the Arctic thread refer to. Reference is made to the distribution of temperatures and heat fluxes and the greatest warming, usually near the ice edge periphery such as around the Barents Sea. Then the more controversial theory (which is getting a lot of exposure right now) that low sea ice extent in late Summer and in the Autumn (Fall) is linked to a -ve NAO the following Winter. (The jury is still out on this one!). There is reference to theories that low sea ice in the Barents and Kara Seas has been associated with strong impacts on lower latitudes. They refer to moisture fluxes from the Arctic to Eurasia coupled with low Arctic ice and greater land mass snow cover there, has an impact on the northern hemisphere circulation and on the atmosphere above. The main changes are theories that the decline in ice extent since 2000 is related to a greater frequency and more extreme cold conditions in central Eurasia and North America. These and further theories on perceived impacts are mentioned. The authors do emphasise that the time period for all these changes and potential impacts is very short (this is where I feel that particular caution is required). They also state, "the climate system is complex and many variables have changed over the last years, which makes it uncertain if the sea ice really is the main driver for mid-latitude climate events". They say that some of the changes may be more influenced by changes in the Atlantic and the Pacific (such as changes in SST anomalies). The authors state how they tested some of these theories - they say "this present study uses by far largest number of models for coordinated sensitivity experiments. We use these large ensemble simulations to investigate the effect of sea ice variations on climate variations in mid and high latitude land areas." They go through what they investigated and the model experiments and data employed. I will now jump to the results and quote part of that. " The experiments show that Arctic sea ice variations largely capture the observed decadal variations in winter Arctic temperature, but not those in mid-latitudes"...." the warm Arctic temperature anomalies after 2005 extend into the mid-latitudes in EXP1. EXP2 shows generally small mid-latitude T2m anomalies, indicating little impact of the sea ice variations on zonally averaged mid-latitude temperature anomalies". For North America the experiment shows or reconfirms that "the SST-forcing seems to be the main driver of winter temperature variations, which is consistent with the dominant teleconnection from the tropical Pacific region. The El Niño Southern Oscillation is known to drive the Pacific North American Pattern in winter, which has a dominant impact on the winter climate over North America." " SST is the main driver for interannual variation. Thus, using climatological SST boundary conditions is not reducing the internal variability in EXP2 as one might expect." The experiments did suggest some correlation In respect of colder Northern European Winters and this became more of the focus: "In the following, we focus on the coldest observed winters in N Europe; we selected those winters from the detrended ERA-interim data, which exceed an anomaly of − 1.5 standard deviations (which means T2m anomalies exceeding −3 K). Based on this criterion, the four winters 1984/1985 (DJF 1985), 1986/1987 (DJF 1987), 2009/2010 (DJF 2010) and 2010/2011 (DJF 2011) are selected. These winters were also some of the coldest winters over Central and Eastern Europe and larger parts of Asia and have in common that anomalously easterly or northeasterly winds advect cold air to N Europe, as seen in the ERA-interim data (Figs. 6, 7). These winds are related to a pronounced NAO-like pattern with positive SLP anomalies over the Nordic Seas and the Arctic and negative SLP anomalies over the North Atlantic that are associated with anticy - clonic anomalies from Scandinavia to the Ural Mountains, and low pressure anomalies south of it. DJF 1987 and DJF 2011 show at the same time a negative SLP-anomaly over the Aleutian Islands, while in DJF 1985 and DJF 2010, positive SLP anomalies occur in the North Pacific; these are consistent with ENSO teleconnection (Di Lorenzo et al. 2010), as weak to moderate El Niño conditions are observed in 1987 and 2010, and La Niña conditions in 1985 and 2011. There is a lot more on this with numerous charts. There is also more reference to the North Atlantic and Pacific. The conclusions - after referring to the shortcomings, they say: "our model experiments reveal robust results across our six atmosphere models. The correlation between winter T2m variations in EXP1 and ERA-interim data is high for all ocean areas but lower over land. However, the T2m average over most of ten different mid and high latitude continental sub domains is significantly correlated with the ERA-interim data. In contrast, T2m in EXP2 is only significantly correlated with ERAinterim over the Arctic Ocean, in northern Europe and northeastern North America. This indicates that sea ice variations have only a limited impact on T2m variations in most mid and high northern latitude regions. Further, the suggested warm Arctic—cold continent pattern (Overland et al. 2011). is only partly reproduced in EXP1 and not reproduced in EXP2 as a response to lower boundary and radiative forcing. Thus, according to our experiments this pattern is unlikely to be due to sea ice variations in reality and might represent internal atmospheric circulation variability. The ice variations are important for the interannual variations of winter T2m in N Europe although the amplitude of the anomalies in the multi-model ensemble mean is about three times smaller than in ERA-interim. This is mainly due to a large spread of simulated T2m-anomalies across the individual ensemble members and shows that many ensemble members are needed to simulate the observed T2m variations over N Europe. November sea ice anomalies in the Beaufort Sea seems to play an important role for the T2m in N Europe in the following winter. They are highly negatively correlated with winter sea ice in the Barents Sea. Those in turn contribute thermodynamically to T2m anomalies in N Europe. Our results revealed a robust response of the ice impact on N Europe T2m across the individual model ensemble means. The T2m in N Europe of each single model ensemble mean is significantly correlated with ERA-interim. However, as for the multi-model ensemble mean, the amplitude of the single model ensemble mean T2m responses are about three times weaker than the observed anomalies (Fig. 2). Such characteristics of the ensemble response may be related to the forced one-way interaction in our AGCM simulations, when the simulated ensemble mean response represents a feedback from the SST and sea ice anomalies originally caused by internal atmosphere variability (Bretherton and Battisti 2000). However, it could also suggest a too weak atmospheric response to surface forcing (Eade et al. 2014). The sea ice conditions in the four coldest observed winters (exceeding cold anomalies of 1.5 standard deviations) in ERA-interim in N Europe since 1982, increase the probability for cold winters in N Europe in the models. However, only few ensemble members simulate T2m anomalies that are as large as the observed ones in these winters. Further, we found that T2m and SLP amplitudes and patterns in the coldest simulated winters in N Europe (which can differ from the observed winters) in the models since 1982 agree well with the coldest winters in ERA-interim. This shows that the models are able to realistically reproduce large-scale circulation and T2m anomaly patterns during extremely cold winters in N Europe. Thus, the fact that the models do not fully reproduce the observed cold winters in these specific winters is not caused by a general failure of the models to reproduce large scale conditions and processes that cause cold winters in N Europe. Therefore, we conclude, that the occurrence of the observed extremely cold winters in these specific years is mainly due to natural variations of the atmospheric circulation and only to a smaller part caused by the underlying sea ice and SST conditions. The results from our study, in contrast to those studies, which suggested a clear link between sea ice and mid latitude cold winters, do not reveal a robust sea ice impact. Our results suggest instead the major role of internal variability for the recent climate anomalies in lower latitudes. When I first skimmed through this paper a few months ago, I felt that their experiments were confirming the relationship between low sea ice extent and northern hemisphere temperatures. Although there is some correlation between regional low sea ice and Eurasian and North European Winters, the experiments and the authors' conclusion relate this to various other factors as well. I feel that we need more years to provide further evidence but logically, as low sea ice extent has been present in almost all the last 10 winters and indeed back to the early 2000s, then one might expect there to be more consistent and frequent impacts. Of course, the interaction of low sea ice extent and a warmer Arctic with other teleconnections needs to be thoroughly investigated. In some seasons/years certain teleconnections might be more dominant but in other years different ones might be. So, without completely dismissing the more direct correlations and theories, this paper does come to rather different conclusions to many previous papers earlier in the decade and up to late 2017. The next paper goes a lot further! Paper 2: Minimal influence of reduced Arctic sea ice on coincident cold winters in mid-latitudes - Published 12th August, 2019 Link to portal entry Abstract: Observations show that reduced regional sea-ice cover is coincident with cold mid-latitude winters on interannual timescales. However, it remains unclear whether these observed links are causal, and model experiments suggest that they might not be. Here we apply two independent approaches to infer causality from observations and climate models and to reconcile these sources of data. Models capture the observed correlations between reduced sea ice and cold mid-latitude winters, but only when reduced sea ice coincides with anomalous heat transfer from the atmosphere to the ocean, implying that the atmosphere is driving the loss. Causal inference from the physics-based approach is corroborated by a lead–lag analysis, showing that circulation-driven temperature anomalies precede, but do not follow, reduced sea ice. Furthermore, no mid-latitude cooling is found in modelling experiments with imposed future sea-ice loss. Our results show robust support for anomalous atmospheric circulation simultaneously driving cold mid-latitude winters and mild Arctic conditions, and reduced sea ice having a minimal influence on severe mid-latitude winters. Link to full paper: Unfortunately this fascinating very recent paper is still behind the "Nature Climate Change" paywall. I'm not a subscriber but if anyone is, then here's the link: https://www.nature.com/articles/s41558-019-0551-4 If/when the paper becomes freely available, the link will appear here. In the meantime, if anyone does have a link (with permissions), please PM me or "reply to topic" below. Then I can add the link sooner and I can give you credit for finding the paper. I did find several articles about this paper which provide a little more detail: https://phys.org/news/2019-08-arctic-sea-ice-loss-minimal-severe.html It is a shame that this very recent paper is behind a paywall. The article that I provide a link to is worth repeating in full here: "Arctic sea-ice loss has 'minimal influence' on severe cold winter weather, research shows - by University of Exeter The dramatic loss of Arctic sea ice through climate change has only a "minimal influence" on severe cold winter weather across Asia and North America, new research has shown. The possible connection between Arctic sea-ice loss and extreme cold weather—such as the deep freezes that can grip the USA in the winter months—has long been studied by scientists. Observations show that when the regional sea-ice cover is reduced, swathes of Asia and North America often experience unusually cold and hazardous winter conditions. However, previous climate modelling studies have suggested that reduced sea ice cannot fully explain the cold winters. Now, a new study by experts from the University of Exeter, the Royal Netherlands Meteorological Institute and the Energy and Sustainability Research Institute in Groningen, has shed new light on the link between sea-ice loss and cold winters. For the research, the international team combined observations over the past 40 years with results from sophisticated climate modelling experiments. They found that the observations and models agreed that reduced regional sea ice and cold winters often coincide which each other. They found that the correlation between reduced sea ice and extreme winters across the mid-latitude occurs because both are simultaneously driven by the same, large-scale atmospheric circulation patterns. Crucially, it shows that reduced sea ice only has a minimal influence on whether a harsh and severe winter will occur. The study is published in leading science journal, Nature Climate Change. Dr. Russell Blackport, a Mathematics Research Fellow at the University of Exeter and lead author of the paper said: "The correlation between reduced sea ice and cold winters does not mean one is causing the other. We show that the real cause is changes in atmospheric circulation which moves warm air into the Arctic and cold air into the mid-latitudes." Over recent decades, the Arctic region has experienced warming temperatures through climate change, which has led to a large decline in sea-ice cover. This reduction in sea-ice cover means that areas of open water increase, which in turn allows the ocean to lose more heat to the atmosphere in winter—this can potentially alter the weather and climate, even well outside the Arctic. Recent studies have suggested that the reduced sea ice or Arctic warming has contributed to recent cold winters experienced in the mid-latitude region—and that as the sea-ice reduces further through climate change, cold winters will become more frequent and severe. Now, this new study suggests that reduced sea ice is not the main cause of the cold winters. Instead, the cold winters are likely caused by random fluctuations in the atmospheric circulation. Professor James Screen, an Associate Professor in Climate Science at the University of Exeter said: "The are many reasons to be concerned about the dramatic loss of Arctic sea ice, but an increased risk of severe winters in North America and Asia is not one of them." Dr. John Fyfe, a Research Scientist at the Canadian Centre for Climate Modelling and Analysis, who was not involved in the research, writes in Nature Climate Change: "Blackport and colleagues put to rest the notion that Arctic sea-ice loss caused the cold mid-latitude winters, showing instead that atmospheric circulation changes preceded, and then simultaneously drove sea-ice loss and mid-latitude cooling". So this paper shows that many of the factors that are changing the Arctic climate are also changing large scale atmospheric circulation and mid latitude climate patterns and the correlations and "cause and effect" relationships are much weaker than many earlier studies have suggested. Obviously we need to see further research supporting (or rejecting) the conclusions of this paper. What I feel that we all need to do is perhaps to "think outside of the box" - assess the macro influences and then how these all interact. In many ways this is what the study of Teleconnections is all about. Arctic sea ice extent and amplification/warming are just two of many. David
  6. A REVIEW OF ARCTIC AMPLIFICATION AND LOW ICE EXTENT IMPACTS ON NORTHERN HEMISPHERE CIRCULATION PATTERNS AND TEMPERATURE In recent years there has been a great deal of research into the impacts of the changing Arctic ice profile and how this influences the Northern Hemisphere now and going forward. I have read a number of excellent papers on this topic and placed a few of them into the Research Portal with many more to be added in the coming weeks and months. I shall review the last two entries in this post. Before that, as some of you already know, I take a very balanced view on Climate Change. I feel that there are too extremists at both ends of the debate and some papers are skewed or even use dubious data to support their biased views. This makes it much harder to try and understand the actual facts and to analyse what is really going on. Even when one is satisfied with the source and authenticity of what is presented, there are some highly conflicting conclusions. I am not going to attempt to come to any specific conclusions myself as I wish to keep an open mind and I realise that there is so much more research required. As many of the experts cannot agree on much of this, I do not believe that anyone can seriously be persuaded one way or the other - but these two papers may change a few minds! In any event, I want to provoke an ongoing debate on this forum as the potential impacts (or lack of them) have ramifications on broader global patterns and the interaction with other teleconnections and very much on medium, seasonal and long range forecasts. Last year I did a post on how low ice extent appeared to impact on changes on the strength, direction and position of the jet stream and I reviewed a couple of excellent papers back then - well things have moved on apace since then! I see that a number of members have already looked at these two papers in the portal, so they are definitely provoking some interest. I decided to place this post on the Arctic thread as we can generate a long term discussion here. The topic is just as relevant to the Teleconnections thread and the 2019-20 Winter Seasonal Discussion thread. I shall copy it on to both of those threads too and also on to the new UK and European Discussion thread. . Paper 1: Impact of Arctic sea ice variations on winter temperature anomalies in northern hemispheric land areas - Published 30th July, 2018 Link to portal entry Abstract: Coordinated numerical ensemble experiments with six different state-of-the-art atmosphere models have been used in order to evaluate the respective impact of the observed Arctic sea ice and sea surface temperature (SST) variations on air temperature variations in mid and high latitude land areas. Two sets of experiments have been designed; in the first set (EXP1), observed daily sea ice concentration and SST variations are used as lower boundary forcing over 1982–2014 while in the second set (EXP2) the SST variations are replaced by the daily SST climatology. The observed winter 2 m air temperature (T2m) variations are relatively well reproduced in a number of mid and high latitude land areas in EXP1, with best agreement in southwestern North America and northern Europe. Sea ice variations are important for the interannual T2m variations in northern Europe but have limited impact on all other mid and high latitude land regions. In particular, sea ice variations do not contribute to the observed opposite variations in the Arctic and mid latitude in our model experiments. The spread across ensemble members is large and many ensemble members are required to reproduce the observed T2m variations over northern Europe in our models. The amplitude of T2m anomalies in the coldest observed winters over northern Europe is not reproduced by our multi-model ensemble means. However, the sea ice conditions in these respective winters and mainly the thermodynamic response to the ice anomalies lead to an enhanced likelihood for occurrence of colder than normal winters and extremely cold winters. Still, the main reason for the observed extreme cold winters is internal atmospheric dynamics. The coldest simulated northern European winters in EXP1 and EXP2 between 1982 and 2014 show the same large scale T2m and atmospheric circulation anomaly patterns as the observed coldest winters, indicating that the models are well able to reproduce the processes, which cause these cold anomalies. The results are robust across all six models used in this study. Link to full paper: https://link.springer.com/content/pdf/10.1007%2Fs00382-018-4305-1.pdf My Review: The introduction goes though some of the rapid changes in Arctic temps during the last decade and correctly stating that the mean temps in the wider Arctic region have risen by more than 2c since 1850 which is 2 to 3 times faster than the rise in global temps. Some of the known causes of this are stated with reference to a number of other papers. Temperature feedback loops are mentioned as well as the extreme variations in snow cover in the surrounding land masses - another subject that I've posted on frequently and will not repeat now accept to say that the snow cover itself is (or was) believed to have influences on the atmosphere (eg: Judah Cohen's correlation theory with early season/October snow extent in Eurasia and Siberia and its impact on potential SSWs and minor warmings). Then the rapid decline in overall Arctic ice extent is outlined - something which many of the posts on the Arctic thread refer to. Reference is made to the distribution of temperatures and heat fluxes and the greatest warming, usually near the ice edge periphery such as around the Barents Sea. Then the more controversial theory (which is getting a lot of exposure right now) that low sea ice extent in late Summer and in the Autumn (Fall) is linked to a -ve NAO the following Winter. (The jury is still out on this one!). There is reference to theories that low sea ice in the Barents and Kara Seas has been associated with strong impacts on lower latitudes. They refer to moisture fluxes from the Arctic to Eurasia coupled with low Arctic ice and greater land mass snow cover there, has an impact on the northern hemisphere circulation and on the atmosphere above. The main changes are theories that the decline in ice extent since 2000 is related to a greater frequency and more extreme cold conditions in central Eurasia and North America. These and further theories on perceived impacts are mentioned. The authors do emphasise that the time period for all these changes and potential impacts is very short (this is where I feel that particular caution is required). They also state, "the climate system is complex and many variables have changed over the last years, which makes it uncertain if the sea ice really is the main driver for mid-latitude climate events". They say that some of the changes may be more influenced by changes in the Atlantic and the Pacific (such as changes in SST anomalies). The authors state how they tested some of these theories - they say "this present study uses by far largest number of models for coordinated sensitivity experiments. We use these large ensemble simulations to investigate the effect of sea ice variations on climate variations in mid and high latitude land areas." They go through what they investigated and the model experiments and data employed. I will now jump to the results and quote part of that. " The experiments show that Arctic sea ice variations largely capture the observed decadal variations in winter Arctic temperature, but not those in mid-latitudes"...." the warm Arctic temperature anomalies after 2005 extend into the mid-latitudes in EXP1. EXP2 shows generally small mid-latitude T2m anomalies, indicating little impact of the sea ice variations on zonally averaged mid-latitude temperature anomalies". For North America the experiment shows or reconfirms that "the SST-forcing seems to be the main driver of winter temperature variations, which is consistent with the dominant teleconnection from the tropical Pacific region. The El Niño Southern Oscillation is known to drive the Pacific North American Pattern in winter, which has a dominant impact on the winter climate over North America." " SST is the main driver for interannual variation. Thus, using climatological SST boundary conditions is not reducing the internal variability in EXP2 as one might expect." The experiments did suggest some correlation In respect of colder Northern European Winters and this became more of the focus: "In the following, we focus on the coldest observed winters in N Europe; we selected those winters from the detrended ERA-interim data, which exceed an anomaly of − 1.5 standard deviations (which means T2m anomalies exceeding −3 K). Based on this criterion, the four winters 1984/1985 (DJF 1985), 1986/1987 (DJF 1987), 2009/2010 (DJF 2010) and 2010/2011 (DJF 2011) are selected. These winters were also some of the coldest winters over Central and Eastern Europe and larger parts of Asia and have in common that anomalously easterly or northeasterly winds advect cold air to N Europe, as seen in the ERA-interim data (Figs. 6, 7). These winds are related to a pronounced NAO-like pattern with positive SLP anomalies over the Nordic Seas and the Arctic and negative SLP anomalies over the North Atlantic that are associated with anticy - clonic anomalies from Scandinavia to the Ural Mountains, and low pressure anomalies south of it. DJF 1987 and DJF 2011 show at the same time a negative SLP-anomaly over the Aleutian Islands, while in DJF 1985 and DJF 2010, positive SLP anomalies occur in the North Pacific; these are consistent with ENSO teleconnection (Di Lorenzo et al. 2010), as weak to moderate El Niño conditions are observed in 1987 and 2010, and La Niña conditions in 1985 and 2011. There is a lot more on this with numerous charts. There is also more reference to the North Atlantic and Pacific. The conclusions - after referring to the shortcomings, they say: "our model experiments reveal robust results across our six atmosphere models. The correlation between winter T2m variations in EXP1 and ERA-interim data is high for all ocean areas but lower over land. However, the T2m average over most of ten different mid and high latitude continental sub domains is significantly correlated with the ERA-interim data. In contrast, T2m in EXP2 is only significantly correlated with ERAinterim over the Arctic Ocean, in northern Europe and northeastern North America. This indicates that sea ice variations have only a limited impact on T2m variations in most mid and high northern latitude regions. Further, the suggested warm Arctic—cold continent pattern (Overland et al. 2011). is only partly reproduced in EXP1 and not reproduced in EXP2 as a response to lower boundary and radiative forcing. Thus, according to our experiments this pattern is unlikely to be due to sea ice variations in reality and might represent internal atmospheric circulation variability. The ice variations are important for the interannual variations of winter T2m in N Europe although the amplitude of the anomalies in the multi-model ensemble mean is about three times smaller than in ERA-interim. This is mainly due to a large spread of simulated T2m-anomalies across the individual ensemble members and shows that many ensemble members are needed to simulate the observed T2m variations over N Europe. November sea ice anomalies in the Beaufort Sea seems to play an important role for the T2m in N Europe in the following winter. They are highly negatively correlated with winter sea ice in the Barents Sea. Those in turn contribute thermodynamically to T2m anomalies in N Europe. Our results revealed a robust response of the ice impact on N Europe T2m across the individual model ensemble means. The T2m in N Europe of each single model ensemble mean is significantly correlated with ERA-interim. However, as for the multi-model ensemble mean, the amplitude of the single model ensemble mean T2m responses are about three times weaker than the observed anomalies (Fig. 2). Such characteristics of the ensemble response may be related to the forced one-way interaction in our AGCM simulations, when the simulated ensemble mean response represents a feedback from the SST and sea ice anomalies originally caused by internal atmosphere variability (Bretherton and Battisti 2000). However, it could also suggest a too weak atmospheric response to surface forcing (Eade et al. 2014). The sea ice conditions in the four coldest observed winters (exceeding cold anomalies of 1.5 standard deviations) in ERA-interim in N Europe since 1982, increase the probability for cold winters in N Europe in the models. However, only few ensemble members simulate T2m anomalies that are as large as the observed ones in these winters. Further, we found that T2m and SLP amplitudes and patterns in the coldest simulated winters in N Europe (which can differ from the observed winters) in the models since 1982 agree well with the coldest winters in ERA-interim. This shows that the models are able to realistically reproduce large-scale circulation and T2m anomaly patterns during extremely cold winters in N Europe. Thus, the fact that the models do not fully reproduce the observed cold winters in these specific winters is not caused by a general failure of the models to reproduce large scale conditions and processes that cause cold winters in N Europe. Therefore, we conclude, that the occurrence of the observed extremely cold winters in these specific years is mainly due to natural variations of the atmospheric circulation and only to a smaller part caused by the underlying sea ice and SST conditions. The results from our study, in contrast to those studies, which suggested a clear link between sea ice and mid latitude cold winters, do not reveal a robust sea ice impact. Our results suggest instead the major role of internal variability for the recent climate anomalies in lower latitudes. When I first skimmed through this paper a few months ago, I felt that their experiments were confirming the relationship between low sea ice extent and northern hemisphere temperatures. Although there is some correlation between regional low sea ice and Eurasian and North European Winters, the experiments and the authors' conclusion relate this to various other factors as well. I feel that we need more years to provide further evidence but logically, as low sea ice extent has been present in almost all the last 10 winters and indeed back to the early 2000s, then one might expect there to be more consistent and frequent impacts. Of course, the interaction of low sea ice extent and a warmer Arctic with other teleconnections needs to be thoroughly investigated. In some seasons/years certain teleconnections might be more dominant but in other years different ones might be. So, without completely dismissing the more direct correlations and theories, this paper does come to rather different conclusions to many previous papers earlier in the decade and up to late 2017. The next paper goes a lot further! Paper 2: Minimal influence of reduced Arctic sea ice on coincident cold winters in mid-latitudes - Published 12th August, 2019 Link to portal entry Abstract: Observations show that reduced regional sea-ice cover is coincident with cold mid-latitude winters on interannual timescales. However, it remains unclear whether these observed links are causal, and model experiments suggest that they might not be. Here we apply two independent approaches to infer causality from observations and climate models and to reconcile these sources of data. Models capture the observed correlations between reduced sea ice and cold mid-latitude winters, but only when reduced sea ice coincides with anomalous heat transfer from the atmosphere to the ocean, implying that the atmosphere is driving the loss. Causal inference from the physics-based approach is corroborated by a lead–lag analysis, showing that circulation-driven temperature anomalies precede, but do not follow, reduced sea ice. Furthermore, no mid-latitude cooling is found in modelling experiments with imposed future sea-ice loss. Our results show robust support for anomalous atmospheric circulation simultaneously driving cold mid-latitude winters and mild Arctic conditions, and reduced sea ice having a minimal influence on severe mid-latitude winters. Link to full paper: Unfortunately this fascinating very recent paper is still behind the "Nature Climate Change" paywall. I'm not a subscriber but if anyone is, then here's the link: https://www.nature.com/articles/s41558-019-0551-4 If/when the paper becomes freely available, the link will appear here. In the meantime, if anyone does have a link (with permissions), please PM me or "reply to topic" below. Then I can add the link sooner and I can give you credit for finding the paper. I did find several articles about this paper which provide a little more detail: https://phys.org/news/2019-08-arctic-sea-ice-loss-minimal-severe.html It is a shame that this very recent paper is behind a paywall. The article that I provide a link to is worth repeating in full here: "Arctic sea-ice loss has 'minimal influence' on severe cold winter weather, research shows - by University of Exeter The dramatic loss of Arctic sea ice through climate change has only a "minimal influence" on severe cold winter weather across Asia and North America, new research has shown. The possible connection between Arctic sea-ice loss and extreme cold weather—such as the deep freezes that can grip the USA in the winter months—has long been studied by scientists. Observations show that when the regional sea-ice cover is reduced, swathes of Asia and North America often experience unusually cold and hazardous winter conditions. However, previous climate modelling studies have suggested that reduced sea ice cannot fully explain the cold winters. Now, a new study by experts from the University of Exeter, the Royal Netherlands Meteorological Institute and the Energy and Sustainability Research Institute in Groningen, has shed new light on the link between sea-ice loss and cold winters. For the research, the international team combined observations over the past 40 years with results from sophisticated climate modelling experiments. They found that the observations and models agreed that reduced regional sea ice and cold winters often coincide which each other. They found that the correlation between reduced sea ice and extreme winters across the mid-latitude occurs because both are simultaneously driven by the same, large-scale atmospheric circulation patterns. Crucially, it shows that reduced sea ice only has a minimal influence on whether a harsh and severe winter will occur. The study is published in leading science journal, Nature Climate Change. Dr. Russell Blackport, a Mathematics Research Fellow at the University of Exeter and lead author of the paper said: "The correlation between reduced sea ice and cold winters does not mean one is causing the other. We show that the real cause is changes in atmospheric circulation which moves warm air into the Arctic and cold air into the mid-latitudes." Over recent decades, the Arctic region has experienced warming temperatures through climate change, which has led to a large decline in sea-ice cover. This reduction in sea-ice cover means that areas of open water increase, which in turn allows the ocean to lose more heat to the atmosphere in winter—this can potentially alter the weather and climate, even well outside the Arctic. Recent studies have suggested that the reduced sea ice or Arctic warming has contributed to recent cold winters experienced in the mid-latitude region—and that as the sea-ice reduces further through climate change, cold winters will become more frequent and severe. Now, this new study suggests that reduced sea ice is not the main cause of the cold winters. Instead, the cold winters are likely caused by random fluctuations in the atmospheric circulation. Professor James Screen, an Associate Professor in Climate Science at the University of Exeter said: "The are many reasons to be concerned about the dramatic loss of Arctic sea ice, but an increased risk of severe winters in North America and Asia is not one of them." Dr. John Fyfe, a Research Scientist at the Canadian Centre for Climate Modelling and Analysis, who was not involved in the research, writes in Nature Climate Change: "Blackport and colleagues put to rest the notion that Arctic sea-ice loss caused the cold mid-latitude winters, showing instead that atmospheric circulation changes preceded, and then simultaneously drove sea-ice loss and mid-latitude cooling". So this paper shows that many of the factors that are changing the Arctic climate are also changing large scale atmospheric circulation and mid latitude climate patterns and the correlations and "cause and effect" relationships are much weaker than many earlier studies have suggested. Obviously we need to see further research supporting (or rejecting) the conclusions of this paper. What I feel that we all need to do is perhaps to "think outside of the box" - assess the macro influences and then how these all interact. In many ways this is what the study of Teleconnections is all about. Arctic sea ice extent and amplification/warming are just two of many. David
  7. Yes, but they should never discontinue it, unless there are plans for an alternative. There has always been more than one American model run, even if you go back to the days of the NGM and LFM.
  8. They said in the release that they won’t discontinue it until the GFS improves in several areas that the NAM is consistently better at...so, probably years. The ensembles were rainier than the GFS and Euro op a few days out.
  9. Well, we have other globals, but it's good to have an American alternative. There has always been more than one American operational model.
  10. The NWS relies on the GFS way to much and weighs their forecasts heavily on it which is a mistake IMO.
  11. And NWS wants to defund the NAM. I think they need to rethink that.
  12. Steady light to moderate rain falling here. Picked up 0.23" of rain so far today.
  13. The CMC has it as more of a cutter type system. The ECMWF seems to like it more Sunday, but as a coastal.
  14. I know at least the GFS has it, is that what the Euro is showing as well?
  15. This is exactly what I was talking about in previous posts. Lets get the storm track down for the winter and then worry about getting the cold air in here. If we can get the cold air to start draining in here anywhere from the third week of November into the first week of December then I think we are in good shape. I like where we sit right now with the storm track.
  16. Perfect timing of the outer edge stacked clouds and the sunrise! Thanks bud! Looking forward to tracking soon and our conversations to share our thoughts.
  17. PSV not a meltdown but joking and poking at the tv mets. 55* and raining here now.
  18. Oh well. Forecast here all week said rain in the afternoon. Nothing changed. Yesterday was always the nicer day
  19. I took this sunrise shot this AM over Skaneateles Lake. We were on the outer edge of the remnants of Nestor and it allowed for a sensational show!
  20. These October coastals set up the pattern for the winter. I say yes every time.
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