New Research

[knocker]

Sea-level rise due to polar ice-sheet mass loss during past warm periods

 

OUTLOOK

Our present climate is warming to a level associated with significant polar ice-sheet loss in the past, but a number of challenges remain to further constrain ice-sheet sensitivity to climate change using paleo–sea level records. Improving our understanding of rates of GMSL rise due to polar ice-mass loss is perhaps the most societally relevant information the paleorecord can provide, yet robust estimates of rates of GMSL rise associated with polar ice-sheet retreat and/or collapse remain a weakness in existing sea-level reconstructions. Improving existing magnitudes, rates, and sources of GMSL rise will require a better (global) distribution of sea-level reconstructions with high temporal resolution and precise elevations and should include sites close to present and former ice sheets. Translating such sea-level data into a robust GMSL signal demands integration with geophysical models, which in turn can be tested through improved spatial and temporal sampling of coastal records.

 

Further development is needed to refine estimates of past sea level from geochemical proxies. In particular, paired oxygen isotope and Mg/Ca data are currently unable to provide confident, quantitative estimates of peak sea level during these past warm periods. In some GMSL reconstructions, polar ice-sheet retreat is inferred from the total GMSL budget, but identifying the specific ice-sheet sources is currently hindered by limited field evidence at high latitudes. Given the paucity of such data, emerging geochemical and geophysical techniques show promise for identifying the sectors of the ice sheets that were most vulnerable to collapse in the past and perhaps will be again in the future.

 

http://www.sciencemag.org/content/349/6244/aaa4019.short

 

Article

 

http://www.sciencedaily.com/releases/2015/07/150709145159.htm

[knocker]

Increased Arctic sea ice volume after anomalously low melting in 2013

 

Changes in Arctic sea ice volume affect regional heat and freshwater budgets and patterns of atmospheric circulation at lower latitudes. Despite a well-documented decline in summer Arctic sea ice extent by about 40% since the late 1970s, it has been difficult to quantify trends in sea ice volume because detailed thickness observations have been lacking. Here we present an assessment of the changes in Northern Hemisphere sea ice thickness and volume using five years of CryoSat-2 measurements. Between autumn 2010 and 2012, there was a 14% reduction in Arctic sea ice volume, in keeping with the long-term decline in extent. However, we observe 33% and 25% more ice in autumn 2013 and 2014, respectively, relative to the 2010–2012 seasonal mean, which offset earlier losses. This increase was caused by the retention of thick sea ice northwest of Greenland during 2013 which, in turn, was associated with a 5% drop in the number of days on which melting occurred—conditions more typical of the late 1990s. In contrast, springtime Arctic sea ice volume has remained stable. The sharp increase in sea ice volume after just one cool summer suggests that Arctic sea ice may be more resilient than has been previously considered.

 

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2489.html

[knocker]

Robust comparison of climate models with observations using blended land air and ocean sea surface temperatures

 

Abstract

The level of agreement between climate model simulations and observed surface temperature change is a topic of scientific and policy concern. While the Earth system continues to accumulate energy due to anthropogenic and other radiative forcings, estimates of recent surface temperature evolution fall at the lower end of climate model projections. Global mean temperatures from climate model simulations are typically calculated using surface air temperatures, while the corresponding observations are based on a blend of air and sea surface temperatures. This work quantifies a systematic bias in model-observation comparisons arising from differential warming rates between sea surface temperatures and surface air temperatures over oceans. A further bias arises from the treatment of temperatures in regions where the sea ice boundary has changed. Applying the methodology of the HadCRUT4 record to climate model temperature fields accounts for 38% of the discrepancy in trend between models and observations over the period 1975-2014.

 

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064888/full

 

Article from the University of York

 

http://www-users.york.ac.uk/~kdc3/papers/robust2015/background.html

[BornFromTheVoid]

Robust comparison of climate models with observations using blended land air and ocean sea surface temperatures

 

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064888/full

 

Article from the University of York

 

http://www-users.york.ac.uk/~kdc3/papers/robust2015/background.html

 

 

 

Also, the authors had a Q&A session on reddit yesterday, which anyone can read through here https://www.reddit.com/r/science/comments/3flzb4/science_ama_series_climate_models_are_more/

[knocker]

Geoengineering is ‘no substitute’ for cutting emissions, new studies show

 

Attempts to limit climate change by removing carbon dioxide directly from the atmosphere would not prevent the irreversible damage to the oceans, according to a new study.

 

While a second study finds that brightening clouds to reflect more of the Sun's radiation could help boost crop yields in parts of China and Africa.

 

http://www.carbonbrief.org/blog/2015/08/geoengineering-is-no-substitute-for-cutting-emissions/?utm_source=Daily+Carbon+Briefing&utm_campaign=44cb04b0c8-cb_daily&utm_medium=email&utm_term=0_876aab4fd7-44cb04b0c8-303447709

[knocker]

Wind effect on the Atlantic meridional overturning circulation via sea ice and vertical diffusion

 

Abstract

Effects of wind and fresh water on the Atlantic meridional overturning circulation (AMOC) are investigated using a fully coupled climate model. The AMOC can change significantly when perturbed by either wind stress or freshwater flux in the North Atlantic. This study focuses on wind stress effect. Our model results show that the wind forcing is crucial in maintaining the AMOC. Reducing wind forcing over the ocean can cause immediately weakening of the vertical salinity diffusion and convection in the mid-high latitudes Atlantic, resulting in an enhancement of vertical salinity stratification that restrains the deep water formation there, triggering a slowdown of the thermohaline circulation. As the thermohaline circulation weakens, the sea ice expands southward and melts, providing the upper ocean with fresh water that weakens the thermohaline circulation further. The wind perturbation experiments suggest a positive feedback between sea-ice and thermohaline circulation strength, which can eventually result in a complete shutdown of the AMOC. This study also suggests that sea-ice variability may be also important to the natural AMOC variability on decadal and longer timescales.

 

Open Access

 

http://rd.springer.com/article/10.1007%2Fs00382-015-2774-z

[knocker]

Timing and climate forcing of volcanic eruptions for the past 2,500 years

 

 

Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing.

http://www.nature.com/articles/nature14565.epdf?referrer_access_token=BNXdtdGKGKIzYX_KSkrl8dRgN0jAjWel9jnR3ZoTv0M9lz4iHAojmG2C7H07L1eAyZHC0nOknOdfjKJEVK4SDqNOtgh2nTmks83KfUalio1IMtnlGj_kREcI5uSU3BGI53LlPR3SYwe7fCE-DWOaz1itSuHSwNYd2-KfzDB1emQcOfF1YFJzQUdrbbDvxkdJk0FcZY4PBuQQ4KK6r0ei_bhfFrLK4DQy4a1dd95xlgIMwHWTQME3Jz_7zRfbJ8cM&tracking_referrer=www.realclimate.org

 

Article here

 

 

Historical Implications

This new dating scheme improves understanding of volcanic forcing effects before the 1^st millennium. For example, 15 of the 16 coldest summers between 500 BC and AD 1000 follow immediately after volcanic events, four of which are found shortly after the largest volcanic events in the record. It also confirms that the so-called “AD 536 event†was a two-stage event, with two large eruptions, a Northern hemisphere eruption in AD 536, and tropical eruption in AD 540, causing over a decade of poor climate and hardship on human civilisation. As we’ve mentioned previously, these eruptions may even have paved the way for the Justinian plague to take hold after AD 540, which is estimated to have killed about one third of the European population, and may also have impacted the Maya civilisation.

The new chronology also shows that the GICC05 date of 1104 for a volcanic horizon attributed to the historical eruption of the Icelandic volcano Hekla is erroneous. Since this horizon is now dated to AD 1108/9 it cannot be associated with Hekla, explaining why attempts to identify Hekla tephra in ice cores in this layer were unproductive (Coulter et al., 2012). It also confirms that the dating of the historical eruption of Eldgja to 934 is also incorrect, its actual eruption date being AD 939. And of course, the acid and tephra signal which was thought to have originated with the AD 79 Vesuvius eruption (Barbante et al., 2013), cannot possibly be due to Vesuvius, this layer now being dated to AD 88.

The one thing not mentioned though is how the error in GICC05 originated. The ice core dates for Eldgja and Hekla of 934 and 1104 have been in print since 1980 (Hammer et al., 1980), and they have been replicated in each Greenland ice core up to now, culminating in the GICC05 timescale. There are similar offsets with Antarctica ice cores that have been dated independently of the GICC05 timescale. An understanding of the origin of this error could help to evaluate the robustness of all ice core dating.

- See more at: http://www.realclimate.org/index.php/archives/2015/08/ice-core-dating-corroborates-tree-ring-chronologies/#ITEM-18645-3

[BornFromTheVoid]

Problems in ocean acidification research...

 

Experimental design in ocean acidification research: problems and solutions

 

Ocean acidification has been identified as a risk to marine ecosystems, and substantial scientific effort has been expended on investigating its effects, mostly in laboratory manipulation experiments. However, performing these manipulations correctly can be logistically difficult, and correctly designing experiments is complex, in part because of the rigorous requirements for manipulating and monitoring seawater carbonate chemistry. To assess the use of appropriate experimental design in ocean acidification research, 465 studies published between 1993 and 2014 were surveyed, focusing on the methods used to replicate experimental units. The proportion of studies that had interdependent or non-randomly interspersed treatment replicates, or did not report sufficient methodological details was 95%. Furthermore, 21% of studies did not provide any details of experimental design, 17% of studies otherwise segregated all the replicates for one treatment in one space, 15% of studies replicated CO2 treatments in a way that made replicates more interdependent within treatments than between treatments, and 13% of studies did not report if replicates of all treatments were randomly interspersed. As a consequence, the number of experimental units used per treatment in studies was low (mean = 2.0). In a comparable analysis, there was a significant decrease in the number of published studies that employed inappropriate chemical methods of manipulating seawater (i.e. acid–base only additions) from 21 to 3%, following the release of the “Guide to best practices for ocean acidification research and data reporting†in 2010; however, no such increase in the use of appropriate replication and experimental design was observed after 2010. We provide guidelines on how to design ocean acidification laboratory experiments that incorporate the rigorous requirements for monitoring and measuring carbonate chemistry with a level of replication that increases the chances of accurate detection of biological responses to ocean acidification.

 

 

Review of the article: http://www.nature.com/news/crucial-ocean-acidification-models-come-up-short-1.18124

[knocker]

The mechanisms of North Atlantic CO₂ uptake in a large Earth System Model ensemble

 

Abstract. The oceans currently take up around a quarter of the carbon dioxide (CO₂) emitted by human activity. While stored in the ocean, this CO₂ is not influencing Earth's radiation budget; the ocean CO₂ sink therefore plays an important role in mitigating global warming. CO₂ uptake by the oceans is heterogeneous, with the subpolar North Atlantic being the strongest CO₂ sink region. Observations over the last 2 decades have indicated that CO₂ uptake by the subpolar North Atlantic sink can vary rapidly. Given the importance of this sink and its apparent variability, it is critical that we understand the mechanisms behind its operation. Here we explore the combined natural and anthropogenic subpolar North Atlantic CO₂ uptake across a large ensemble of Earth System Model simulations, and find that models show a peak in sink strength around the middle of the century after which CO₂ uptake begins to decline. We identify different drivers of change on interannual and multidecadal timescales. Short-term variability appears to be driven by fluctuations in regional seawater temperature and alkalinity, whereas the longer-term evolution throughout the coming century is largely occurring through a counterintuitive response to rising atmospheric CO₂ concentrations. At high atmospheric CO₂ concentrations the contrasting Revelle factors between the low latitude water and the subpolar gyre, combined with the transport of surface waters from the low latitudes to the subpolar gyre, means that the subpolar CO₂ uptake capacity is largely satisfied from its southern boundary rather than through air–sea CO₂ flux. Our findings indicate that: (i) we can explain the mechanisms of subpolar North Atlantic CO₂ uptake variability across a broad range of Earth System Models; (ii) a focus on understanding the mechanisms behind contemporary variability may not directly tell us about how the sink will change in the future; (iii) to identify long-term change in the North Atlantic CO₂ sink we should focus observational resources on monitoring lower latitude as well as the subpolar seawater CO₂; (iv) recent observations of a weakening subpolar North Atlantic CO₂ sink may suggest that the sink strength has peaked and is in long-term decline.

 

Open Access

 

http://www.biogeosciences.net/12/4497/2015/bg-12-4497-2015.html

[knocker]

Spotty sunspot record gets a makeover

Astronomers fine-tune a data set stretching back four centuries.

 

 

Astronomers have fixed an embarrassing discrepancy involving the longest observational record in science: data on sunspot activity that stretch back four centuries. The discovery has ramifications for understanding how the Sun has affected, and could still affect, life on Earth.

 

Notably, the revised sunspot tally shows that solar activity has not risen in recent decades, as once thought¹. Some had linked this idea of a sunspot 'Grand Maximum' to hotter temperatures on Earth.

 

“We find no such Grand Maximum,†says Frédéric Clette, an astronomer at the Royal Observatory of Belgium in Brussels. “There has been nothing exceptional about the level of solar activity.â€

 

http://www.nature.com/news/spotty-sunspot-record-gets-a-makeover-1.18145?WT.mc_id=TWT_NatureNews

[knocker]

Scientists Pioneer Method to Track Water Flowing Through Glaciers

 

AUSTIN, Texas â€” Researchers for the first time have used seismic sensors to track meltwater flowing through glaciers and into the ocean, an essential step to understanding the future of the world’s largest glaciers as climate changes.

 

The University of Texas Institute for Geophysics (UTIG) helped pioneer this new method on glaciers in Greenland and Alaska. The study will be published Aug. 10 in the journal Geophysical Research Letters.

 

Meltwater moving through a glacier into the ocean is critically important because it can increase melting and destabilize the glacier in a number of ways: The water can speed the glacier’s flow downhill toward the sea; it can move rocks, boulders and other sediments toward the terminus of the glacier along its base; and it can churn and stir warm ocean water, bringing it in contact with the glacier.

 

http://news.utexas.edu/2015/08/10/scientists-pioneer-method-to-track-water-flowing-in-glaciers

[knocker]

Modeled and observed increases in extreme summer heat events 

 

http://iopscience.iop.org/1748-9326/8/3/034018/pdf/1748-9326_8_3_034018.pdf â€¦

[knocker]

Role of the strengthened El Niño teleconnection in the May 2015 floods over the southern Great Plains

 

The climate anomalies leading to the May 2015 floods in Texas and Oklahoma were analyzed in the context of El Niño teleconnection in a warmer climate. El Niño tends to increase late-spring precipitation in the southern Great Plains and this effect has intensified since 1980. There was a detectable effect of anthropogenic global warming in the physical processes that caused the persistent precipitation in May of 2015: Warming in the tropical Pacific acted to strengthen the teleconnection towards North America, modification of zonal wave-5 circulation that deepened the anomalous trough to the west of Texas, and an enhanced Great Plains low-level southerlies increasing moisture supply from the Gulf of Mexico. Attribution analysis using the CMIP5 single-forcing experiments and the CESM Large Ensemble Project indicated a significant increase in the El Niño-induced precipitation anomalies over Texas and Oklahoma when increases in the anthropogenic greenhouse gases were taken into account.

 

http://onlinelibrary.wiley.com/doi/10.1002/2015GL065211/full

[knocker]

Heat Release from Stagnant Deep Sea Helped End Last Ice Age

 

The build-up and subsequent release of warm, stagnant water from the deep Arctic Ocean and Nordic Seas played a role in ending the last Ice Age within the Arctic region, according to new research led by an international team of scientists.

 

The study, published today in Science, examines how the circulation of the combined Arctic Ocean and Nordic Seas – called the Arctic Mediterranean – changed since the end of the last Ice Age (~20,000-30,000 years ago). The results highlight the important impact that changes in ocean circulation can have on climate.

 

http://www.whoi.edu/news-release/stagnant-deep-sea

 

Paper

 

http://www.sciencemag.org/content/349/6249/706

Edited August 14, 2015 by knocker

[knocker]

ENSO and greenhouse warming

 

The El Niño/Southern Oscillation (ENSO) is the dominant climate phenomenon affecting extreme weather conditions worldwide. Its response to greenhouse warming has challenged scientists for decades, despite model agreement on projected changes in mean state. Recent studies have provided new insights into the elusive links between changes in ENSO and in the mean state of the Pacific climate. The projected slow-down in Walker circulation is expected to weaken equatorial Pacific Ocean currents, boosting the occurrences of eastward-propagating warm surface anomalies that characterize observed extreme El Niño events. Accelerated equatorial Pacific warming, particularly in the east, is expected to induce extreme rainfall in the eastern equatorial Pacific and extreme equatorward swings of the Pacific convergence zones, both of which are features of extreme El Niño. The frequency of extreme La Niña is also expected to increase in response to more extreme El Niños, an accelerated maritime continent warming and surface-intensified ocean warming. ENSO-related catastrophic weather events are thus likely to occur more frequently with unabated greenhouse-gas emissions. But model biases and recent observed strengthening of the Walker circulation highlight the need for further testing as new models, observations and insights become available.

 

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2743.html

 

Discussion

 

http://www.carbonbrief.org/blog/2015/08/climate-change-set-to-fuel-more-monster-el-ni%C3%B1os,-scientists-warn/?utm_source=Daily+Carbon+Briefing&utm_campaign=bec57af12e-cb_daily&utm_medium=email&utm_term=0_876aab4fd7-bec57af12e-303447709

[BornFromTheVoid]

Another study to back up the "Hockey Stick", and put most of the blame on the cooling trend into the LIA on volcanoes rather than solar or orbital variations.

 

Robust global ocean cooling trend for the pre-industrial Common Era

 

The oceans mediate the response of global climate to natural and anthropogenic forcings. Yet for the past 2,000 years — a key interval for understanding the present and future climate response to these forcings — global sea surface temperature changes and the underlying driving mechanisms are poorly constrained. Here we present a global synthesis of sea surface temperatures for the Common Era (CE) derived from 57 individual marine reconstructions that meet strict quality control criteria. We observe a cooling trend from 1 to 1800 CE that is robust against explicit tests for potential biases in the reconstructions. Between 801 and 1800 CE, the surface cooling trend is qualitatively consistent with an independent synthesis of terrestrial temperature reconstructions, and with a sea surface temperature composite derived from an ensemble of climate model simulations using best estimates of past external radiative forcings. Climate simulations using single and cumulative forcings suggest that the ocean surface cooling trend from 801 to 1800 CE is not primarily a response to orbital forcing but arises from a high frequency of explosive volcanism. Our results show that repeated clusters of volcanic eruptions can induce a net negative radiative forcing that results in a centennial and global scale cooling trend via a decline in mixed-layer oceanic heat content.

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2510.html

 

 

Review of the article here http://phys.org/news/2015-08-years-global-ocean-cooling-halted.html

[knocker]

Contribution of anthropogenic warming to California drought during 2012–2014

 

A suite of climate datasets and multiple representations of atmospheric moisture demand are used to calculate many estimates of the self-calibrated Palmer Drought Severity Index, a proxy for near-surface soil moisture, across California from 1901–2014 at high spatial resolution. Based on the ensemble of calculations, California drought conditions were record-breaking in 2014, but probably not record-breaking in 2012–2014, contrary to prior findings. Regionally, the 2012–2014 drought was record-breaking in the agriculturally important southern Central Valley and highly populated coastal areas. Contributions of individual climate variables to recent drought are also examined, including the temperature component associated with anthropogenic warming. Precipitation is the primary driver of drought variability but anthropogenic warming is estimated to have accounted for 8–27% of the observed drought anomaly in 2012–2014 and 5–18% in 2014. Although natural variability dominates, anthropogenic warming has substantially increased the overall likelihood of extreme California droughts.

 

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064924/full

 

Article

 

http://www.earth.columbia.edu/articles/view/3258

[knocker]

As Ice Age ended, greenhouse gas rise was lead factor in melting of Earth's glaciers

A fresh look at some old rocks has solved a crucial mystery of the last Ice Age, yielding an important new finding that connects to the global retreat of glaciers caused by climate change today, according to a new study by a team of climate scientists.

 

For decades, researchers examining the glacial meltdown that ended 11,000 years ago took into account a number of contributing factors, particularly regional influences such as solar radiation, ice sheets and ocean currents.

 

But a reexamination of more than 1,000 previously studied glacial boulders has produced a more accurate timetable for the pre-historic meltdown and pinpoints the rise in carbon dioxide - then naturally occurring - as the primary driving factor in the simultaneous global retreat of glaciers at the close of the last Ice Age, the researchers report in the journal Nature Communications.

Read more at: http://phys.org/news/2015-08-ice-age-greenhouse-gas-factor.html#jCp

Edited August 21, 2015 by knocker

[BornFromTheVoid]

Learning from mistakes in climate research

 

Among papers stating a position on anthropogenic global warming (AGW), 97 % endorse AGW. What is happening with the 2 % of papers that reject AGW? We examine a selection of papers rejecting AGW. An analytical tool has been developed to replicate and test the results and methods used in these studies; our replication reveals a number of methodological flaws, and a pattern of common mistakes emerges that is not visible when looking at single isolated cases. Thus, real-life scientific disputes in some cases can be resolved, and we can learn from mistakes. A common denominator seems to be missing contextual information or ignoring information that does not fit the conclusions, be it other relevant work or related geophysical data. In many cases, shortcomings are due to insufficient model evaluation, leading to results that are not universally valid but rather are an artifact of a particular experimental setup. Other typical weaknesses include false dichotomies, inappropriate statistical methods, or basing conclusions on misconceived or incomplete physics. We also argue that science is never settled and that both mainstream and contrarian papers must be subject to sustained scrutiny. The merit of replication is highlighted and we discuss how the quality of the scientific literature may benefit from replication.

 

http://link.springer.com/article/10.1007/s00704-015-1597-5

 

Overview of the paper http://www.theguardian.com/environment/climate-consensus-97-per-cent/2015/aug/25/heres-what-happens-when-you-try-to-replicate-climate-contrarian-papers?CMP=share_btn_tw

[knocker]

New NASA videos show stark ice loss from Earth's ice sheets

The US space agency, NASA, yesterday released brand new images showing the pace of ice loss from Earth's two vast ice sheets, Greenland and Antarctica.

 

The amount of ice lost from the frozen expanses at the very north and south of the planet is accelerating, say the scientists, and together have helped raise global sea level by more than 7cm since 1992.

 

http://www.carbonbrief.org/blog/2015/08/new-nasa-videos-show-stark-ice-loss-from-earths-ice-sheets/?utm_source=Daily+Carbon+Briefing&utm_campaign=33ce3d431a-cb_daily&utm_medium=email&utm_term=0_876aab4fd7-33ce3d431a-303447709

Edited August 28, 2015 by knocker

[knocker]

Two distinct influences of Arctic warming on cold winters over North America and East Asia

 

Arctic warming has sparked a growing interest because of its possible impacts on mid-latitude climate^{1, 2, 3, 4, 5}. A number of unusually harsh cold winters have occurred in many parts of East Asia and North America in the past few years^{2, 6, 7}, and observational and modelling studies have suggested that atmospheric variability linked to Arctic warming might have played a central role^{1, 3, 4, 8, 9, 10, 11}. Here we identify two distinct influences of Arctic warming which may lead to cold winters over East Asia or North America, based on observational analyses and extensive climate model results. We find that severe winters across East Asia are associated with anomalous warmth in the Barents–Kara Sea region, whereas severe winters over North America are related to anomalous warmth in the East Siberian–Chukchi Sea region. Each regional warming over the Arctic Ocean is accompanied by the local development of an anomalous anticyclone and the downstream development of a mid-latitude trough. The resulting northerly flow of cold air provides favourable conditions for severe winters in East Asia or North America. These links between Arctic and mid-latitude weather are also robustly found in idealized climate model experiments and CMIP5 multi-model simulations. We suggest that our results may help improve seasonal prediction of winter weather and extreme events in these regions.

 

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2517.html

 

Article

 

http://www.carbonbrief.org/blog/2015/08/arctic-warming-hotspots-behind-severe-northern-hemisphere-winters/?utm_source=Daily+Carbon+Briefing&utm_campaign=836bcb65a2-cb_daily&utm_medium=email&utm_term=0_876aab4fd7-836bcb65a2-303447709

[knocker]

Significant anthropogenic-induced changes of climate classes since 1950

 

Anthropogenic forcings have contributed to global and regional warming in the last few decades and likely affected terrestrial precipitation. Here we examine changes in major Köppen climate classes from gridded observed data and their uncertainties due to internal climate variability using control simulations from Coupled Model Intercomparison Project 5 (CMIP5). About 5.7% of the global total land area has shifted toward warmer and drier climate types from 1950–2010, and significant changes include expansion of arid and high-latitude continental climate zones, shrinkage in polar and midlatitude continental climates, poleward shifts in temperate, continental and polar climates, and increasing average elevation of tropical and polar climates. Using CMIP5 multi-model averaged historical simulations forced by observed anthropogenic and natural, or natural only, forcing components, we find that these changes of climate types since 1950 cannot be explained as natural variations but are driven by anthropogenic factors.

 

Open Access

 

http://www.nature.com/articles/srep13487?WT.ec_id=SREP-20150901&spMailingID=49446297&spUserID=MTM5MjU5MDc5NjY3S0&spJobID=760089552&spReportId=NzYwMDg5NTUyS0#f1

 

Discussion by Greg Laden

 

http://scienceblogs.com/gregladen/2015/09/01/anthropogenic-global-warming-causes-significant-changes-in-climate-zones/

Edited September 1, 2015 by knocker

[knocker]

Talking of the AMO..........................

 

Gradual onset and recovery of the Younger Dryas abrupt climate event in the tropics

 

Proxy records of temperature from the Atlantic clearly show that the Younger Dryas was an abrupt climate change event during the last deglaciation, but records of hydroclimate are underutilized in defining the event. Here we combine a new hydroclimate record from Palawan, Philippines, in the tropical Pacific, with previously published records to highlight a difference between hydroclimate and temperature responses to the Younger Dryas. Although the onset and termination are synchronous across the records, tropical hydroclimate changes are more gradual (>100 years) than the abrupt (10–100 years) temperature changes in the northern Atlantic Ocean. The abrupt recovery of Greenland temperatures likely reflects changes in regional sea ice extent. Proxy data and transient climate model simulations support the hypothesis that freshwater forced a reduction in the Atlantic meridional overturning circulation, thereby causing the Younger Dryas. However, changes in ocean overturning may not produce the same effects globally as in Greenland.

 

http://www.nature.com/ncomms/2015/150902/ncomms9061/full/ncomms9061.html

 

Press release

 

http://www.sciencedaily.com/releases/2015/09/150902082932.htm

[knocker]

Dramatically increased rate of observed hot record-breaking in recent Australian temperatures

 

Persistent extreme temperatures were observed in Australia during 2012-2014. We examine changes in the rate of hot and cold record-breaking over the observational record for Australia- and State-wide temperatures. The number of new hot (high maximum and high minimum temperatures) temperature records increases dramatically in recent decades, while the number of cold records decreases. In a stationary climate, cold and hot records are expected to occur in equal frequency on longer than interannual timescales, however, during 2000-2014, new hot records outnumber new cold records by 12 to one on average. Coupled Model Intercomparison Project phase 5 (CMIP5) experiments reveal increased hot temperature record-breaking occurs in simulations that impose anthropogenic forcings, but not in natural forcings-only experiments. This disproportionate hot to cold record-breaking rates provides a useful indicator of nonstationarity in temperatures, which is related to the underlying mean observed Australian warming trend of 0.9°C since high-quality records began in 1910.

 

http://onlinelibrary.wiley.com/doi/10.1002/2015GL065793/abstract

[knocker]

Latest paper on processes controlling surface, bottom and lateral melt of Arctic sea ice here

 

http://rsta.royalsocietypublishing.org/content/373/2052/20140167.abstract â€¦

 

A tweet from  MichaelTsamados one of the authors

 

"The sea ice orchestra" where @alekpetty discusses our latest paper in a very neat blog post https://alekpetty.wordpress.com/2015/09/07/the-sea-ice-orchestra/ â€¦