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Are sudden stratospheric warmings preceded by anomalous tropospheric wave activity?

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Abstract

A combination of 240 years of output from a state-of-the-art chemistry climate model and a 20th century reanalysis product is used to investigate to what extent sudden stratospheric warmings are preceded by anomalous tropospheric wave activity. To this end we study the fate of lower tropospheric wave events (LTWEs) and their interaction with the stratospheric mean flow. These LTWEs are contrasted with sudden stratospheric deceleration events (SSDs), which are similar to sudden stratospheric warmings but place more emphasis on the explosive dynamical nature of such events. Reanalysis and model output provide very similar statistics: Around one third of the identified SSDs are preceded by wave events in the lower troposphere, while two thirds of the SSDs are not preceded by a tropospheric wave event. In addition, only 20% of all anomalous tropospheric wave events are followed by an SSD in the stratosphere. This constitutes statistically robust evidence that the anomalous amplification of wave activity in the stratosphere that drives SSDs is not necessarily due to an anomalous amplification of the waves in the source region (i.e. the lower troposphere). The results suggest that the dynamics in the lowermost stratosphere and the vortex geometry are essential, and should be carefully analyzed in the search for precursors of SSDs.

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-19-0269.1

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Climate Change Drives Widespread and Rapid Thermokarst Development in Very Cold Permafrost in the Canadian High Arctic

Abstract

Climate warming in regions of ice‐rich permafrost can result in widespread thermokarst
development, which reconfigures the landscape and damages infrastructure. We present multisite time
series observations which couple ground temperature measurements with thermokarst development in a
region of very cold permafrost. In the Canadian High Arctic between 2003 and 2016, a series of anomalously
warm summers caused mean thawing indices to be 150–240% above the 1979–2000 normal resulting in up to
90 cm of subsidence over the 12‐year observation period. Our data illustrate that despite low mean
annual ground temperatures, very cold permafrost (<−10 °C) with massive ground ice close to the surface is
highly vulnerable to rapid permafrost degradation and thermokarst development. We suggest that this is due
to little thermal buffering from soil organic layers and near‐surface vegetation, and the presence of
near‐surface ground ice. Observed maximum thaw depths at our sites are already exceeding those projected
to occur by 2090 under representative concentration pathway version

.
Plain Language Summary

Permafrost is ground that remains at or below 0 °C for two years or
longer and it underlies much of the Arctic. Permafrost in Arctic lowland regions is frequently characterized
by large volumes of ground ice which, when it melts, causes the ground surface to collapse. As the Arctic
warms, ice‐rich permafrost degradation is expected to be widespread. Our data illustrate that very cold
permafrost, which has a mean annual ground temperature of −10 °C or lower, is experiencing a rapid
increase in active layer thickness at annual time scales. At three permafrost monitoring sites in the Canadian
Arctic we have observed that warmer than average summer air temperatures have caused the active layer to
deepen, near‐surface ground ice to melt, and the overlying ground surface to subside, in some cases
leading to the formation of small thaw ponds. Our results show that very cold permafrost terrain is
responding rapidly to ongoing warming.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019GL082187

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The global and regional impacts of climate change under representative concentration pathway forcings and shared socioeconomic pathway socioeconomic scenarios

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Abstract

This paper presents an evaluation of the global and regional consequences of climate change for heat extremes, water resources, river and coastal flooding, droughts, agriculture and energy use. It presents change in hazard and resource base under different rates of climate change (representative concentration pathways (RCP)), and socio-economic impacts are estimated for each combination of RCP and shared socioeconomic pathway. Uncertainty in the regional pattern of climate change is characterised by CMIP5 climate model projections. The analysis adopts a novel approach using relationships between level of warming and impact to rapidly estimate impacts under any climate forcing. The projections provided here can be used to inform assessments of the implications of climate change. At the global scale all the consequences of climate change considered here are adverse, with large increases under the highest rates of warming. Under the highest forcing the global average annual chance of a major heatwave increases from 5% now to 97% in 2100, the average proportion of time in drought increases from 7% to 27%, and the average chance of the current 50 year flood increases from 2% to 7%. The socio-economic impacts of these climate changes are determined by socio-economic scenario. There is variability in impact across regions, reflecting variability in projected changes in precipitation and temperature. The range in the estimated impacts can be large, due to uncertainty in future emissions and future socio-economic conditions and scientific uncertainty in how climate changes in response to future emissions. For the temperature-based indicators, the largest source of scientific uncertainty is in the estimated magnitude of equilibrium climate sensitivity, but for the indicators determined by precipitation the largest source is in the estimated spatial and seasonal pattern of changes in precipitation. By 2100, the range across socio-economic scenario is often greater than the range across the forcing levels.

https://iopscience.iop.org/article/10.1088/1748-9326/ab35a6

Blog

http://blogs.reading.ac.uk/weather-and-climate-at-reading/2019/the-consequences-of-climate-change-how-bad-could-it-get/

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Global impacts of thawing Arctic permafrost may be imminent

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The Arctic permafrost, frozen soil that is chock full of carbon, is a ticking time bomb. When it thaws because of global warming, sometimes slumping into pits like on Herschel Island in Canada (above), scientists believe it is likely to release more carbon than it absorbs from new plant growth—adding to the atmosphere’s burden and accelerating climate change. But studies in the Arctic have been so limited that no one could say when that time would come.

It’s here now, according to research published today by a large team of scientists in Nature Climate Change. By pooling observations from more than 100 Arctic field sites, scientists from the Permafrost Carbon Network estimate that permafrost released an average of 1662 teragrams of carbon each winter from 2003 to 2017—double that of past estimates. Meanwhile, during the summer growing season, other surveys have found that the landscape absorbs only 1032 teragrams—leaving an average of more than 600 teragrams of carbon to escape to the atmosphere each year.

https://www.sciencemag.org/news/2019/10/global-impacts-thawing-arctic-permafrost-may-be-imminent

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How Robust is the Atmospheric Response to Projected Arctic Sea Ice Loss Across Climate Models?

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Abstract

We assess the reliability of an indirect method of inferring the atmospheric response to projected Arctic sea ice loss from CMIP5 simulations, by comparing the response inferred from the indirect method to that explicitly simulated in sea ice perturbation experiments. We find that the indirect approach works well in winter, but has limited utility in the other seasons. We then apply a modified version of the indirect method to 11 CMIP5 models to reveal the robust and non‐robust aspects of the wintertime atmospheric response to projected Arctic sea ice loss. Despite limitations of the indirect method, we identify a robust enhancement of the Siberian High, weakening of the Icelandic Low, weakening of the westerly wind on the poleward flank of the eddy‐driven jet, strengthening of the subtropical jet, and weakening of the stratospheric polar vortex. The surface air temperature response to projected Arctic sea ice loss over mid‐latitude continents is non‐robust across the models.

Plain Language Summary

The continued melt of Arctic sea ice will likely affect weather and climate in places far from the Arctic. To better understand the far‐flung implications of sea ice loss, scientists can perform bespoke climate model experiments in which sea ice is reduced, but all other climate drivers are fixed. In our paper, we test the reliability of an indirect method to infer the atmospheric response to sea ice loss, which makes use of a large set of climate model experiments originally performed for other purposes. We find that the indirect approach works well in winter, but not so well in other seasons. We then apply the indirect method to 11 climate models to reveal the robust and non‐robust aspects of the wintertime atmospheric response to projected Arctic sea ice loss—the largest such comparison to date. We found that the models agreed on quite a few aspects of the response, including warming over the Arctic, regional surface pressure changes over Siberia and Iceland, and a slowing of the mid‐latitude jet stream. On the other hand, the models disagreed on whether surface air temperatures over Europe, North America, and East Asia will warm or cool in response to future Arctic sea ice loss.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL084936

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Northern Hemisphere Stationary Waves in a Changing Climate

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Purpose of Review

Stationary waves are planetary-scale longitudinal variations in the time-averaged atmospheric circulation. Here, we consider the projected response of Northern Hemisphere stationary waves to climate change in winter and summer. We discuss how the response varies across different metrics, identify robust responses, and review proposed mechanisms.

Recent Findings

Climate models project shifts in the prevailing wind patterns, with corresponding impacts on regional precipitation, temperature, and extreme events. Recent work has improved our understanding of the links between stationary waves and regional climate and identified robust stationary wave responses to climate change, which include an increased zonal lengthscale in winter, a poleward shift of the wintertime circulation over the Pacific, a weakening of monsoonal circulations, and an overall weakening of stationary wave circulations, particularly their divergent component and quasi-stationary disturbances.

Summary

Numerous factors influence Northern Hemisphere stationary waves, and mechanistic theories exist for only a few aspects of the stationary wave response to climate change. Idealized studies have proven useful for understanding the climate responses of particular atmospheric circulation features and should be a continued focus of future research.

https://link.springer.com/article/10.1007%2Fs40641-019-00147-6

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New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding

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Most estimates of global mean sea-level rise this century fall below 2 m. This quantity is comparable to the positive vertical bias of the principle digital elevation model (DEM) used to assess global and national population exposures to extreme coastal water levels, NASA’s SRTM. CoastalDEM is a new DEM utilizing neural networks to reduce SRTM error. Here we show – employing CoastalDEM—that 190 M people (150–250 M, 90% CI) currently occupy global land below projected high tide lines for 2100 under low carbon emissions, up from 110 M today, for a median increase of 80 M. These figures triple SRTM-based values. Under high emissions, CoastalDEM indicates up to 630 M people live on land below projected annual flood levels for 2100, and up to 340 M for mid-century, versus roughly 250 M at present. We estimate one billion people now occupy land less than 10 m above current high tide lines, including 250 M below 1 m.

https://www.nature.com/articles/s41467-019-12808-z

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World Scientists’ Warning of a Climate Emergency

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Scientists have a moral obligation to clearly warn humanity of any catastrophic threat and to “tell it like it is.” On the basis of this obligation and the graphical indicators presented below, we declare, with more than 11,000 scientist signatories from around the world, clearly and unequivocally that planet Earth is facing a climate emergency.

https://academic.oup.com/bioscience/advance-article/doi/10.1093/biosci/biz088/5610806

And just to add

EIq7fnXWsAYX9z0.thumb.jpg.517d7d82f1c6c579e335453fb7bc710d.jpg

Edited by knocker

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Atlantic and Pacific oscillations lost in the noise

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UNIVERSITY PARK, Pa. — The Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO) do not appear to exist, according to a team of meteorologists who believe this has implications for both the validity of previous studies attributing past trends to these hypothetical natural oscillations and for the prospects of decade-scale climate predictability.

Using both observational data and climate model simulations, the researchers showed that there was no consistent evidence for decadal or longer-term internal oscillatory signals that could be differentiated from climatic noise — random year to year variation. The only verifiable oscillation is the well-known El Niño/Southern Oscillation (ENSO).

https://news.psu.edu/story/602574/2020/01/03/research/atlantic-and-pacific-oscillations-lost-noise

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Climate change now detectable from any single day of weather at global scale

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Abstract

For generations, climate scientists have educated the public that ‘weather is not climate’, and climate change has been framed as the change in the distribution of weather that slowly emerges from large variability over decades1,2,3,4,5,6,7. However, weather when considered globally is now in uncharted territory. Here we show that on the basis of a single day of globally observed temperature and moisture, we detect the fingerprint of externally driven climate change, and conclude that Earth as a whole is warming. Our detection approach invokes statistical learning and climate model simulations to encapsulate the relationship between spatial patterns of daily temperature and humidity, and key climate change metrics such as annual global mean temperature or Earth’s energy imbalance. Observations are projected onto this relationship to detect climate change. The fingerprint of climate change is detected from any single day in the observed global record since early 2012, and since 1999 on the basis of a year of data. Detection is robust even when ignoring the long-term global warming trend. This complements traditional climate change detection, but also opens broader perspectives for the communication of regional weather events, modifying the climate change narrative: while changes in weather locally are emerging over decades, global climate change is now detected instantaneously.

https://www.nature.com/articles/s41558-019-0666-7

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Seasonal Changes in the North Atlantic Cold Anomaly: The Influence of Cold Surface Waters From Coastal Greenland and Warming Trends Associated With Variations in Subarctic Sea Ice Cover

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Abstract

Worldwide sea surface temperatures (SST) have increased on average by about 1 °C since 1900 with the exception of a region of the North Atlantic subpolar gyre near 50°N which has cooled by up to 0.9 °C over the same period, generating the negative feature on temperature anomaly maps which has been colloquially described by Rahmstorf et al. (2015, https://doi.org/10.1038/nclimate2554) as the “cold blob” (abbreviated here CB). This unique long‐term surface cooling trend is most evident in February, but in August net warming is observed even at CB epicenter and the CB itself is reduced to a mere “warming hole.” These seasonal changes in the intensity of the CB are the product of two separate factors: (1) a long‐term winter cooling specific for the CB region which appears to be associated with cooling of Greenland coastal waters in autumn, plausibly linked to summer meltwater from icebergs and sea ice and (2) summer warming effects which derive from (a) dramatic reduction in summer sea ice cover in the sub‐Arctic over the last 30 years that allows enhanced absorption of sunlight by the new open water in summer and (b) an unusual period of increased summer sub‐Arctic ice cover in the early twentieth century, which lowers the SST baseline measured from 1900, thus increasing the calculated linear rate of change of SST with time. Both of these effects could contribute to the observed Arctic amplification of warming.

Plain Language Summary

In a world which has notably warmed by about 1 °C over the last 100 years, the “cold blob” represents a unique ocean surface region in the central North Atlantic which paradoxically has cooled by almost 1 °C over the same period. We show here that the intensity and coherence of the cold blob is greatest in winter, but its development appears to be connected with a surface cooling of water near the SE coast of Greenland in late autumn. This pool of cold water is likely to have its origin in summer meltwater from the Greenland ice sheet and sea‐ice and we suggest ways in which it could reach and sustain the cold blob. In summer the cold blob disappears because it is overwhelmed by warming influences associated with past and current reductions in sea ice cover in the coastal sub‐Arctic regions of the NW Atlantic. These warming influences associated with reductions in sea ice are part of the reason why Arctic temperatures have recently risen faster than anywhere else.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JC015379

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Causes of higher climate sensitivity in CMIP6 models

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Abstract

Equilibrium climate sensitivity, the global surface temperature response to CO$_2$ doubling, has been persistently uncertain. Recent consensus places it likely within 1.5‐4.5K. Global climate models (GCMs), which attempt to represent all relevant physical processes, provide the most direct means of estimating climate sensitivity via CO$_2$ quadrupling experiments. Here we show that the closely related effective climate sensitivity has increased substantially in Coupled Model Intercomparison Project phase 6 (CMIP6), with values spanning 1.8‐5.6K across 27 GCMs and exceeding 4.5K in 10 of them. This (statistically insignificant) increase is primarily due to stronger positive cloud feedbacks from decreasing extratropical low cloud coverage and albedo. Both of these are tied to the physical representation of clouds which in CMIP6 models lead to weaker responses of extratropical low cloud cover and water content to unforced variations in surface temperature. Establishing the plausibility of these higher sensitivity models is imperative given their implied societal ramifications.

Plain Language Summary

The severity of climate change is closely related to how much the Earth warms in response to greenhouse gas increases. Here we find that the temperature response to an abrupt quadrupling of atmospheric carbon dioxide has increased substantially in the latest generation of global climate models. This is primarily because low cloud water content and coverage decrease more strongly with global warming, causing enhanced planetary absorption of sunlight ‐‐ an amplifying feedback that ultimately results in more warming. Differences in the physical representation of clouds in models drive this enhanced sensitivity relative to the previous generation of models. It is crucial to establish whether the latest models, which presumably represent the climate system better than their predecessors, are also providing a more realistic picture of future climate warming.

Key Points

Climate sensitivity is larger on average in CMIP6 than in CMIP5 due mostly to a stronger positive low cloud feedback

This is due to greater reductions in low cloud cover and weaker increases in low cloud water content, primarily in the extratropics

These changes are related to model physics differences that are apparent in unforced climate variability

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL085782

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Rapid Response Review shows human-induced climate change promotes the conditions on which wildfires depend, increasing their likelihood.

In light of the Australian fires, scientists from the University of East Anglia (UEA), Met Office Hadley Centre, University of Exeter, Imperial College London, and CSIRO Oceans and Atmosphere, have conducted a Rapid Response Review of 57 peer-reviewed papers published since the IPCC's Fifth Assessment Report in 2013.

All the studies show links between climate change and increased frequency or severity of fire weather - periods with a high fire risk due to a combination of high temperatures, low humidity, low rainfall and often high winds - though some note anomalies in a few regions.

Professor Richard Betts, Head of Climate Impacts Research at the Met Office Hadley Centre and co-author of the report, said: “Fire weather does occur naturally but is becoming more severe and widespread due to climate change. Limiting global warming to well below 2°C would help avoid further increases in the risk of extreme fire weather.”

The full report is hosted on the ScienceBrief website and can be accessed here. 

https://sciencebrief.org/briefs/wildfires

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Looks like the back end of this year will see some useful data emerging on the role of 'clouds' in our present, and future, warming?

Since day one of the 'Climate Debate' (for me.....back in the BBC's 'Slow Watch' days...) anyone having issues with AGW would either appear to use the 'uncertainties' of the impacts of cloud as a reason to dismiss ALL predictions around AGW impacts or hold them as proving that things will not be as bad as predictions made them (as 'clouds' would prove to be some 'self balancing mechanism' keeping the planet cool?)

Well, at last, it looks like we will have real world data of a scale as to end such mis/disinformation?

Cloud_flowers_JADU.jpg
WWW.LEEDS.AC.UK

UK scientists are taking to the skies as part of a major international research campaign to better understand the behaviour of clouds and their role in climate change.

 

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About half of the Arctic warming and sea ice loss between 1955 and 2005 may be explained by ozone depleting substances.

 

41558_2019_677_Fig1_HTML.png
WWW.NATURE.COM

Arctic warming is attributed to GHGs and feedbacks, but the specific contribution of ozone-depleting substances (ODS)—also potent GHGs—has never been quantified. Here, model simulations show that ODS...

 

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The Atlantic Ocean fingerprint on the climate of the Middle East

CMCC Foundation - Euro-Mediterranean Center on Climate Change

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The Atlantic Ocean acts as a key pacemaker for Middle East surface air temperature (ME-SAT) multidecadal variability in summer. This is the important result of a study published on NPJ Climate and Atmospheric Science unveiling and demonstrating the existence of a North Atlantic-Middle East teleconnection, that is a remote influence of the Atlantic multidecadal variability on the decadal variability of Middle East summer temperatures. This Atlantic-ME summer connection involves ocean-atmosphere interactions through multiple ocean basins, with an influence from the Indian Ocean and the Arabian Sea.

https://www.eurekalert.org/pub_releases/2020-01/cf-e-tao012820.php

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The forgotten drought of 1,765–1,768: Reconstructing and re‐evaluating historical droughts in the British and Irish Isles

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Abstract

Historical precipitation records are fundamental for the management of water resources, yet rainfall observations typically span 100–150 years at most, with considerable uncertainties surrounding earlier records. Here, we analyse some of the longest available precipitation records globally, for England and Wales, Scotland and Ireland. To assess the credibility of these records and extend them further back in time, we statistically reconstruct (using independent predictors) monthly precipitation series representing these regions for the period 1,748–2000. By applying the Standardised Precipitation Index at 12‐month accumulations (SPI‐12) to the observed and our reconstructed series we re‐evaluate historical meteorological droughts. We find strong agreement between observed and reconstructed drought chronologies in post‐1870 records, but divergence in earlier series due to biases in early precipitation observations. Hence, the 1800s decade was less drought prone in our reconstructions relative to observations. Overall, the drought of 1834–1836 was the most intense SPI‐12 event in our reconstruction for England and Wales. Newspaper accounts and documentary sources confirm the extent of impacts across England in particular. We also identify a major, “forgotten” drought in 1765–1,768 that affected the British‐Irish Isles. This was the most intense event in our reconstructions for Ireland and Scotland, and ranks first for accumulated deficits across all three regional series. Moreover, the 1,765–1,768 event was also the most extreme multi‐year drought across all regional series when considering 36‐month accumulations (SPI‐36). Newspaper and other sources confirm the occurrence and major socio‐economic impact of this drought, such as major rivers like the Shannon being fordable by foot. Our results provide new insights into historical droughts across the British Irish Isles. Given the importance of historical droughts for stress‐testing the resilience of water resources, drought plans and supply systems, the forgotten drought of 1,765–1,768 offers perhaps the most extreme benchmark scenario in more than 250‐years.

https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/joc.6521

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New Generation of Climate Models Track Recent Unprecedented Changes in Earth's Radiation Budget Observed by CERES

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Abstract

We compare top‐of‐atmosphere (TOA) radiative fluxes observed by the Clouds and the Earth's Radiant Energy System (CERES) and simulated by seven general circulation models forced with observed sea‐surface temperature (SST) and sea‐ice boundary conditions. In response to increased SSTs along the equator and over the eastern Pacific (EP) following the so‐called global warming “hiatus” of the early 21st century, simulated TOA flux changes are remarkably similar to CERES. Both show outgoing shortwave and longwave TOA flux changes that largely cancel over the west and central tropical Pacific, and large reductions in shortwave flux for EP low‐cloud regions. A model's ability to represent changes in the relationship between global mean net TOA flux and surface temperature depends upon how well it represents shortwave flux changes in low‐cloud regions, with most showing too little sensitivity to EP SST changes, suggesting a “pattern effect” that may be too weak compared to observations.

Plain Language Summary

Earth's radiation budget describes the balance between radiation from the sun intercepted by Earth and radiation returned back to space through reflection of solar radiation and emission of terrestrial thermal infrared radiation. This balance is a fundamental property of Earth's climate system as it describes how Earth gains and sheds heat. Here we use observations from the Clouds and the Earth's Radiant Energy System (CERES) to evaluate how seven state‐of‐the‐art climate models represent changes in Earth's radiation budget during and following the so‐called global warming “hiatus” of the early 21st century. The models were provided observed sea‐surface temperature and sea‐ice boundary conditions as well as natural and anthropogenic forcings. We find remarkable agreement between observed and simulated differences in reflected solar and emitted thermal infrared radiation between the post‐hiatus and hiatus periods. Furthermore, a model's ability to correctly relate Earth's radiation budget and surface temperature is found to depend upon how well it represents reflected solar radiation changes in regions dominated by low clouds, particularly those over the eastern Pacific ocean.

 

 

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL086705

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Insignificant effect of Arctic amplification on the amplitude of midlatitude atmospheric waves

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Abstract

Whether Arctic amplification has contributed to a wavier circulation and more frequent extreme weather in midlatitudes remains an open question. For two to three decades starting from the mid-1980s, accelerated Arctic warming and a reduced meridional near-surface temperature gradient coincided with a wavier circulation. However, waviness remains largely unchanged in model simulations featuring strong Arctic amplification. Here, we show that the previously reported trend toward a wavier circulation during autumn and winter has reversed in recent years, despite continued Arctic amplification, resulting in negligible multidecadal trends. Models capture the observed correspondence between a reduced temperature gradient and increased waviness on interannual to decadal time scales. However, model experiments in which a reduced temperature gradient is imposed do not feature increased wave amplitude. Our results strongly suggest that the observed and simulated covariability between waviness and temperature gradients on interannual to decadal time scales does not represent a forced response to Arctic amplification.

https://advances.sciencemag.org/content/6/8/eaay2880

Press release

Jet stream not getting ‘wavier’ despite Arctic warming

http://www.exeter.ac.uk/news/homepage/title_778916_en.html

 

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I mooted ,back nearly a decade ago, that when other areas of the Arctic (i.e. the Pacific side of the basin would enter the fray?) saw the same level of impact as Barrentsz/Kara then the 'asymmetry' of the basin would end and it would revert back toward its 'old' configuration (a PNJ not showing a tendency for 'lobes'?) and this years PNJ would seem to indicate a return to its 'old' shape and function?

This ,in its turn, must have impact on the Polar Jet?

Edited by Gray-Wolf

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7 minutes ago, Gray-Wolf said:

I mooted ,back nearly a decade ago, that when other areas of the Arctic saw the same level of impact as Barentsz/Kara the 'asymmetry' of the basin would revert back toward its 'old' configuration (a PNJ not showing a tendency for 'lobes'?) and this years PNJ would seem to indicate a return to its 'old' shape and function?

This ,in its turn, must have impact on the Polar Jet?

My first thought was that this is at variance with Dr, Francis, et al but of course they discussed that

Quote

If Arctic amplification is not a cause of increased waviness, a logical next question to ask is where in the proposed chain of causality does the Francis and Vavrus hypothesis break down. Recall that the hypothesis states that Arctic amplification reduces the westerly wind and that a slower flow is wavier. In our simulations, we do find a modest but statistically significant decrease in strength of the westerly winds over mid- and high latitudes in response to Arctic amplification, consistent with similar modeling experiments using other models and protocols (46). So, the proposed connection between Arctic amplification and a slower westerly flow appears sound, at least qualitatively. However, a slower westerly flow forced by Arctic amplification does not result in a wavier circulation. This appears to be the weak link in the proposed chain. Changes in wave amplitude are governed by factors in addition to the westerly wind strength, including baroclinicity, moisture, lower tropospheric heating, and tropical wave driving (4).

 

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