New Research

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The polar amplification asymmetry: role of Antarctic surface height

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I apologise for breaking into the stream of politics for some science: Temperatures in the Arctic are increasing around three times as fast as the global average, yet the pace of warming has been much slower at Earth’s other pole. A new study, just published in Earth System Dynamics, suggests the difference might – in part – be down to the great heights of Antarctica’s land surface. The article is The polar amplification asymmetry: role of Antarctic surface height by Marc Salzmann. And since it’s open-access I’m sure they won’t mind me copying from their abstract:

http://scienceblogs.com/stoat/2017/05/20/the-polar-amplification-asymmetry-role-of-antarctic-surface-height/

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How Variations in Earth’s Orbit Triggered the Ice Ages

Researchers pinpoint how Milankovitch cycles have driven ice growth and influenced the timing of glacial periods.

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For millennia, Earth’s climate has hinged on the behavior of ice: the cycle of glacier growth and retreat. These alternating glacial and interglacial periods coincide with variations in Earth’s orbit called Milankovitch cycles, which affect the insolation, or sunlight exposure, of different regions and thus the behavior of ice formation.

The average length of glacial periods has changed over time, from cycles of roughly 40,000 years that were more closely aligned to changes in obliquity—the tilt of Earth’s axis—to cycles of roughly 100,000 years, coinciding with changes in the eccentricity, or shape, of our planet’s orbit. The transition between 40,000- and 100,000-year cycles last occurred in the mid-Pleistocene. However, scientists have struggled to identify exactly how ice ages start, why they line up with these cycles, and why the lengths of and gaps between glacial periods vary through time.

https://eos.org/research-spotlights/how-variations-in-earths-orbit-triggered-the-ice-ages

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Global risk of deadly heat

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Climate change can increase the risk of conditions that exceed human thermoregulatory capacity1, 2, 3, 4, 5, 6. Although numerous studies report increased mortality associated with extreme heat events1, 2, 3, 4, 5, 6, 7, quantifying the global risk of heat-related mortality remains challenging due to a lack of comparable data on heat-related deaths2, 3, 4, 5. Here we conducted a global analysis of documented lethal heat events to identify the climatic conditions associated with human death and then quantified the current and projected occurrence of such deadly climatic conditions worldwide. We reviewed papers published between 1980 and 2014, and found 783 cases of excess human mortality associated with heat from 164 cities in 36 countries. Based on the climatic conditions of those lethal heat events, we identified a global threshold beyond which daily mean surface air temperature and relative humidity become deadly. Around 30% of the world’s population is currently exposed to climatic conditions exceeding this deadly threshold for at least 20 days a year. By 2100, this percentage is projected to increase to ~48% under a scenario with drastic reductions of greenhouse gas emissions and ~74% under a scenario of growing emissions. An increasing threat to human life from excess heat now seems almost inevitable, but will be greatly aggravated if greenhouse gases are not considerably reduced.

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3322.html

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Oh dear, oh dear oh dear!

A new paper published in the Journal of Climate reveals that the lower part of the Earth’s atmosphere has warmed much faster since 1979 than scientists relying on satellite data had previously thought.

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Researchers from Remote Sensing Systems (RSS), based in California, have released a substantially revised version of their lower tropospheric temperature record.

After correcting for problems caused by the decaying orbit of satellites, as well as other factors, they have produced a new record showing 36% faster warming since 1979 and nearly 140% faster (e.g. 2.4 times faster) warming since 1998. This is in comparison to the previous version 3 of the lower tropospheric temperature (TLT) data published in 2009.

https://www.carbonbrief.org/major-correction-to-satellite-data-shows-140-faster-warming-since-1998

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High risk of unprecedented UK rainfall in the current climate

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In winter 2013/14 a succession of storms hit the UK leading to record rainfall and flooding in many regions including south east England. In the Thames river valley there was widespread flooding, with clean-up costs of over £1 billion. There was no observational precedent for this level of rainfall. Here we present analysis of a large ensemble of high-resolution initialised climate simulations to show that this event could have been anticipated, and that in the current climate there remains a high chance of exceeding the observed record monthly rainfall totals in many regions of the UK. In south east England there is a 7% chance of exceeding the current rainfall record in at least one month in any given winter. Expanding our analysis to some other regions of England and Wales the risk increases to a 34% chance of breaking a regional record somewhere each winter.

https://www.nature.com/articles/s41467-017-00275-3

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WATER-MASS VARIABILITY IN THE SOUTHERN OCEAN:
SEPARATING NATURAL FLUCTUATIONS FROM LONG-TERM CHANGE

http://web.maths.unsw.edu.au/~matthew/southern_ocean_variability.htm

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Interesting little video by Kate Marvel

Climate change is real, case closed. But there's still a lot we don't understand about it, and the more we know the better chance we have to slow it down. One still-unknown factor: How might clouds play a part? There's a small hope that they could buy us some time to fix things ... or they could make global warming worse. Climate scientist Kate Marvel takes us through the science of clouds and what it might take for Earth to break its own fever.

https://www.ted.com/talks/kate_marvel_can_clouds_buy_us_more_time_to_solve_climate_change#t-774996

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This strange spot in the Atlantic is resisting global warming. Scientists think they know why.

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A mysterious “warming hole” in the North Atlantic Ocean, an anomalous zone of cooling temperatures which has fascinated and puzzled scientists for the past few years, may be evidence of more troubling processes at work.

A new study, just out in the journal Nature Climate Change, has joined a growing body of literature suggesting the cold patch is evidence that a major ocean current system — which transports heat and influences climate and weather patterns around the world — may be slowing down. What’s more, the melting of Arctic sea ice could be to blame.

https://www.washingtonpost.com/news/energy-environment/wp/2017/08/02/this-strange-spot-over-the-atlantic-isnt-getting-warmer-scientists-think-they-may-know-why/?utm_term=.1e7947bf7796

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Balloons and drones and clouds; oh, my!

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ALBUQUERQUE, N.M. -- Last week, researchers at Sandia National Laboratories flew a tethered balloon and an unmanned aerial system, colloquially known as a drone, together for the first time to get Arctic atmospheric temperatures with better location control than ever before. In addition to providing more precise data for weather and climate models, being able to effectively operate UASs in the Arctic is important for national security.

"Operating UASs in the remote, harsh environments of the Arctic will provide opportunities to harden the technologies in ways that are directly transferable to the needs of national security in terms of robustness and reliability," said Jon Salton, a Sandia robotics manager. "Ultimately, integrating the specialized operational and sensing needs required for Arctic research will transfer to a variety of national security needs."

https://www.eurekalert.org/pub_releases/2017-08/dnl-bad081417.php

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Ocean circulation, coupled with trade wind changes, efficiently limits shifting of tropical rainfall patterns

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The Intertropical Convergence Zone (ITCZ), also known as the doldrums, is one of the dramatic features of Earth's climate system. Prominent enough to be seen from space, the ITCZ appears in satellite images as a band of bright clouds around the tropics. Here, moist warm air accumulates in this atmospheric region near the equator, where the ocean and atmosphere heavily interact. Intense solar radiation and calm, warm ocean waters produce an area of high humidity, ascending air, and rainfall, which is fed by converging trade winds from the Northern and Southern Hemispheres. The convected air forms clusters of thunderstorms characteristic of the ITCZ, releasing heat before moving away from the ITCZ—toward the poles—cooling and descending in the subtropics. This circulation completes the Hadley cells of the ITCZ, which play an important role in balancing Earth's energy budget—transporting energy between the hemispheres and away from the equator.

https://m.phys.org/news/2017-07-ocean-circulation-coupled-efficiently-limits.html

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CMIP5 models suggest Arctic stratosphere will warm (and polar vortex will weaken) in future climate scenarios: H/t Amy Butler

Arctic Stratosphere Dynamical Response to Global Warming

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The role of stationary planetary waves in the dynamical response of the Arctic winter stratosphere circulation to global warming is investigated here by analyzing simulations performed with atmosphere-only models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) driven by prescribed sea surface temperatures (SSTs). Climate models often simulate dynamical warming of the Arctic stratosphere as a response to global warming in association with a strengthening of the deep branch of the Brewer–Dobson circulation; however, until now, no satisfactory mechanism for such a response has been suggested. This study focuses on December–February (DJF) because this is the period when the troposphere and stratosphere are strongly coupled. When forced by increased SSTs, all the models analyzed here simulate Arctic stratosphere dynamical warming, mostly due to increased upward propagation of quasi-stationary wavenumber 1, as diagnosed by the meridional eddy heat flux. Further, it is shown that the stratospheric warming and increased wave flux to the stratosphere are related to the strengthening of the zonal winds in subtropics and midlatitudes near the tropopause. Evidence presented in this paper corroborate climate model simulations of future stratospheric changes and suggest a dynamical warming of the Arctic polar vortex as the most likely response to global warming.

http://journals.ametsoc.org/doi/10.1175/JCLI-D-16-0781.1

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Influence of Anthropogenic Climate Change on Planetary Wave Resonance and Extreme Weather Events

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Persistent episodes of extreme weather in the Northern Hemisphere summer have been shown to be associated with the presence of high-amplitude quasi-stationary atmospheric Rossby waves within a particular wavelength range (zonal wavenumber 6–8). The underlying mechanistic relationship involves the phenomenon of quasi-resonant amplification (QRA) of synoptic-scale waves with that wavenumber range becoming trapped within an effective mid-latitude atmospheric waveguide. Recent work suggests an increase in recent decades in the occurrence of QRA-favorable conditions and associated extreme weather, possibly linked to amplified Arctic warming and thus a climate change influence. Here, we isolate a specific fingerprint in the zonal mean surface temperature profile that is associated with QRA-favorable conditions. State-of-the-art (“CMIP5”) historical climate model simulations subject to anthropogenic forcing display an increase in the projection of this fingerprint that is mirrored in multiple observational surface temperature datasets. Both the models and observations suggest this signal has only recently emerged from the background noise of natural variability.

https://www.nature.com/articles/srep45242

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Not everybody’s sold on either the general jet-stream wobbliness from a warming Arctic, or the stabilizing atmospheric waves described by Mann, Rahmstorf, and colleagues. “It’s still controversial,” Sobel said. Even Mann, the lead-author, introduced the pattern as “tenuous,” and Rahmstorf said that more real-world case studies and more years of observations are needed.

 

Edited August 30, 2017 by knocker

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Extreme warming in the Kara Sea and Barents Sea during the winter period 2000 to 2016

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The regional climate model COSMO-CLM (CCLM) is used with a high resolution of 15 km for the entire Arctic for all winters 2002/2003-2014/2015. The simulations show a high spatial and temporal variability of the recent 2-m air temperature increase in the Arctic. The maximum warming occurs north of Novaya Zemlya in the Kara Sea and Barents Sea between March 2003-2012 and is responsible for up to 20°C increase. Land-based observations confirm the increase but do not cover the maximum regions that are located over the ocean and sea-ice. Also the 30 km version of the Arctic System Reanalysis (ASR) is used to verify the CCLM for the overlapping time period 2002/2003-2011/2012. The differences between CCLM and ASR 2-m air temperatures vary slightly within 1°C for the ocean and sea-ice area. Thus, ASR captures the extreme warming as well. The monthly 2-m air temperatures of observations and ERA-Interim reanalyses show a large variability for the winters 1979-2016. Nevertheless, the air temperature rise since the beginning of the 21^st century is up to eight times higher than in the decades before. The sea-ice decrease is identified as the likely reason for the warming. The vertical temperature profiles show that the warming has a maximum near the surface, but a 0.5°Cyr⁻¹ increase is found up to 2 km. CCLM, ASR and also the coarser resolved ERA-Interim Reanalysis show that February and March are the months with the highest 2-m air temperature increases, averaged over the ocean and sea-ice area north of 70°N; for CCLM the warming amounts to an average of almost 5°C for 2002/2003-2011/2012.

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0693.1?utm_content=buffer43ac3&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

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Unraveling a major cause of sea ice retreat in the Arctic Ocean

https://phys.org/news/2017-09-unraveling-major-sea-ice-retreat.html

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Rapid response of Helheim Glacier, southeast Greenland, to early Holocene climate warming

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Recent changes in speed, thinning, and retreat rates of marine-terminating outlet glaciers have raised concerns about the future stability of the Greenland Ice Sheet. Establishing a longer term record of outlet glacier retreat rates is essential to provide a context for present-day observations and to improve and constrain numerical models of outlet glacier behavior. New exposure dating (¹⁰Be) of streamlined bedrock surfaces and glacial erratic boulders of Sermilik Fjord, southeast Greenland, the present-day drainage route of Helheim Glacier, documents rapid retreat (∼80 m a⁻¹) of this major marine-terminating outlet glacier at the close of the last glaciation. The glacier front retreated ∼80 km to within 20 km of the present-day (2010) position of Helheim Glacier in <1 ka, ca. 10.8 ± 0.3 ka ago. Retreat followed rapidly rising air temperatures at the start of the Holocene, and at this temporal resolution there is no evidence that fjord geometry influenced glacier behavior. The significant response to climatic amelioration at the end of the last glacial suggests a high sensitivity to abrupt temperature increases, which has major implications for the future stability of present-day Greenlandic outlet glaciers in a warming climate.

https://pubs.geoscienceworld.org/geology/article-abstract/40/5/427/130898/rapid-response-of-helheim-glacier-southeast?redirectedFrom=fulltext

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Ancient tree reveals cause of spike in Arctic temperature

https://phys.org/news/2017-09-ancient-tree-reveals-spike-arctic.html

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Taking the Pulse of the Planet

How fast is Earth warming? Ocean heat content and sea level rise measurements may provide a more reliable answer than atmospheric measurements.

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Decision-makers, scientists, and the general public are faced with critical questions: How fast is Earth’s system accumulating heat, and how much will it warm in the future as human activities continue to emit greenhouse gases?

Here we explore better ways of measuring global warming to answer these questions. Natural temperature variability is much more muted in the ocean than in the atmosphere, owing to the ocean’s greater ability to absorb heat (its heat capacity). As a result, ocean heating and sea level rise, which are measured independently, show stronger evidence that the planet is warming than does global average surface temperature, which relies on air temperature measurements. In other words, these ocean measurements could provide vital signs for the health of the planet.

 

Thus, we suggest that scientists and modelers who seek global warming signals should track how much heat the ocean is storing at any given time, termed global ocean heat content (OHC), as well as sea level rise (SLR). Similar to SLR, OHC has a very high signal-to-noise ratio; that is, it clearly shows the effects of climate change distinct from natural variability.

https://eos.org/opinions/taking-the-pulse-of-the-planet#.WblJZIj-6CU.twitter

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Not new research but an article of general interest I think

After 30 years of the Montreal Protocol, the ozone layer is gradually healing

https://theconversation.com/after-30-years-of-the-montreal-protocol-the-ozone-layer-is-gradually-healing-84051

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Winter cold extremes linked to high-altitude polar vortex weakening

https://phys.org/news/2017-09-winter-cold-extremes-linked-high-altitude.html

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In Hawaii and the Pacific Islands, 2017 has been anything but normal

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The climate of the islands of Hawaii and the Pacific is often characterized by iconic scenes of warm, sandy beaches, blue skies, and swaying palm trees.  However, these scenes can be dramatically transformed when sea levels become anomalously high or low, wave action increases due to nearby storms, and drought or heavy rains impact local food supplies.  In other words, there can be climate trouble even in paradise.

Most regions of the United States fall within major land areas, and their weather and climate are well observed by ground-based stations. However, the tropical Pacific spans thousands of miles on end without land, and this geography makes it difficult to collect weather and climate data effectively. To evaluate climate in this vast ocean region, we must use other sources of data in conjunction with traditional land-based station data. Data from satellites have proven indispensable in meeting these challenges.

https://www.climate.gov/news-features/blogs/beyond-data/hawaii-and-pacific-islands-2017-has-been-anything-normal

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Euro-Mediterranean Heat — Summer 2017

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This year’s summer in Western Europe and the Euro-Mediterranean region has been remarkable in several aspects. Early summer heat during much of June affected western European countries (in particular, France, Switzerland, Belgium, the Netherlands, England, Portugal and Spain). In July, the heat returned to southern Spain. Madrid (Retiro) hit 40.6°C (105°F) on July 13, equal to the record set in 2012. Heat wave episodes continued into August, spreading to Southern Europe. Early August saw a particularly intense heat wave in southeastern countries, with local maximum temperatures in Italy and the Balkans topping 40°C (104°F) for several days. Temperature records were broken in Southern France (Nîmes, Courbessac, 41.6°C/106.9°F) for example, and in Corsica and Croatia, where night-time temperatures remained above 30°C (86°F). Southern Poland also made headlines with abnormally high August temperatures. The heat combined with high humidity was described as the “worst heat wave since 2003” (BBC) in southern countries. Taking the summer months together, this resulted in a hot summer as a whole. In France, for instance, the mean summer temperature was ranked second after 2003 and just above that of 2015.

https://wwa.climatecentral.org/analyses/euro-mediterranean-heat-summer-2017/

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Historical Trends and Variability in Heat Waves in the United Kingdom

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Increases in numbers and lengths of heat waves have previously been identified in global temperature records, including locations within Europe. However, studies of changes in UK heat wave characteristics are limited. Historic daily maximum temperatures from 29 weather stations with records exceeding 85 years in length across the country were examined. Heat waves were defined as periods with unusually high temperatures for each station, even if the temperatures would not be considered warm in an absolute sense. Positive trends in numbers and lengths of heat waves were identified at some stations. However, for some stations in the south east of England, lengths of very long heat waves (over 10 days) had declined since the 1970s, whereas the lengths of shorter heat waves had increased slightly. Considerable multidecadal variability in heat wave numbers and lengths was apparent at all stations. Logistic regression, using a subset of eight stations with records beginning in the nineteenth century, suggested an association between the Atlantic Multidecadal Oscillation and the variability in heat wave numbers and lengths, with the summertime North Atlantic Oscillation playing a smaller role. The results were robust against different temperature thresholds. View Full-Text

http://www.mdpi.com/2073-4433/8/10/191

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Seasonal sensitivity of the Northern Hemisphere jet-streams to Arctic temperatures on subseasonal timescales

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Abstract

Near-surface Arctic warming has been shown to impact the midlatitude jet-streams through the use of carefully designed model simulations with and without Arctic sea ice loss. In this work, we instead take a Granger causality regression approach to quantify the response of the zonal wind to variability of near-surface Arctic temperatures on subseasonal timescales across the CMIP5 models. Using this technique, we demonstrate a robust influence of regional Arctic warming on the North Atlantic and North Pacific jet-stream positions, speeds and zonal winds. However, Arctic temperatures only explain an additional 3-5% of the variance of the winds after accounting for the variance associated with the persistence of the wind anomalies from previous weeks.

In terms of the jet-stream response, the North Pacific and North Atlantic jet-streams consistently shift equatorward in response to Arctic warming, but also strengthen, rather than weaken, during most months of the year. Furthermore, the sensitivity of the jet-stream position and strength to Arctic warming is shown to be a strong function of season. Specifically, in both ocean basins, the jets shift furthest equatorward in the summer months. We argue that this seasonal sensitivity is due to the Arctic-warming-induced wind anomalies remaining relatively fixed in latitude, while the climatological jet migrates in and out of the anomalies throughout the annual cycle. Based on these results, we go on to demonstrate that model differences in the climatological jet-stream position lead to differences in the jet-stream position’s sensitivity to Arctic warming.

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0299.1

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1st to predict global warming: Nobel Laureate Svante Arrhenius. Paper from 1896

http://www.rsc.org/images/Arrhenius1896_tcm18-173546.pdf