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jethro

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Posted
  • Location: Camborne
  • Location: Camborne
Aerosol reductions could account for up to 40 percent of future Arctic sea ice loss

 

 

Anticipated declines in human-produced aerosols could have a significant effect on Arctic sea ice cover over the remainder of the 21st century, accounting for up to 40 percent of the decline in sea ice extent that could occur in the region by 2100, a new study shows.

 

Average ice coverage in the Arctic ranges from about 15 million square kilometers (6 million square miles) in the winter to about 6 million square kilometers (2 million square miles) in the summer, according to the Intergovernmental Panel on Climate Change Fifth Assessment Report. Arctic sea ice extent has been declining since the mid-1970s, largely driven by greenhouse gas-induced warming, according to previous studies.

 

This warming and loss of sea ice has been partially offset by human-generated aerosols. Some types of these small, airborne particles reflect solar radiation away from the Earth and cool the climate. But scientists predict the amount of cooling generated by these aerosols will wane as emissions of these particles fall, causing the climate to warm and sea ice to decline. Aerosol concentrations have dropped in recent decades as developed countries have cut emissions, and emissions are expected to decline even further as other countries follow suit.

 

The new study finds Arctic sea ice cover is expected to decline by 2.5 million square kilometers to 7 million square kilometers (1 million square miles to 2.7 million square miles) by the end of the century, depending on emissions of greenhouse gases, aerosols and other compounds.

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Posted
  • Location: Mytholmroyd, West Yorks.......
  • Weather Preferences: Hot & Sunny, Cold & Snowy
  • Location: Mytholmroyd, West Yorks.......

I think the whole 'particulate/aerosol ' issue will be the 'frightener' that seals the deal on AGW as it is a 'held off' forcing in that the agent for warming ( GHG's) is already aloft but masked meaning the slow move away from 'dirty' pollution will bring a steady positive forcing no matter what the 'naturals ' are doing on top of current AGW forcing.

 

As such 2c looks already lost to us?

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Posted
  • Location: Camborne
  • Location: Camborne

Heat and humidity could make parts of the Middle East ‘unbearable’ by 2100

 

Conditions in the Middle East could become so hot and humid by the end of the century that being outside for more than six hours would be intolerable, a new study says.

 

http://www.carbonbrief.org/heat-and-humidity-could-make-parts-of-the-middle-east-unbearable-by-2100/?utm_source=Daily+Carbon+Briefing&utm_campaign=6316c6b163-cb_daily&utm_medium=email&utm_term=0_876aab4fd7-6316c6b163-303447709

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Posted
  • Location: Camborne
  • Location: Camborne
Less Ice, More Water  New study: Parts of Arctic Ocean shifting rapidly to conditions very different from last century

 

By the 2050s, parts of the Arctic Ocean once covered by sea ice much of the year will see at least 60 additional days a year of open water, according to a new modeling study led by researchers at the University of Colorado Boulder. 

“We hear all the time about how sea ice extent in the Arctic is going down,†says Katy Barnhart, who led the study while at CU-Boulder’s Institute for Arctic and Alpine Research (INSTAAR). “That’s an important measurement if you are trying to understand broad impacts of climate change in the Arctic, but it doesn’t tell us about how the changes in the sea ice in the Arctic are going to affect specific places.†

So Barnhart and her colleagues, including CIRES Fellow Jennifer Kay and INSTAAR Fellow Irina Overeem, set out to investigate the very local impacts of open water expansion patterns in the Arctic. Their work is published today in the journal Nature Climate Change.

 

http://cires.colorado.edu/news/press/openwater/

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Posted
  • Location: Camborne
  • Location: Camborne

Evidence for weakening of the Walker circulation from cloud observations

 

 

Climate models simulate a weakening of the Walker circulation in response to increased greenhouse gases, but it has not been possible to detect this weakening with observations because there are not direct measurements of atmospheric circulation strength. Indirect measurements, such as equatorial gradients in sea level pressure (SLP), exhibit trends of inconsistent sign. In this study we estimate the change in midtropospheric velocity (ω500) from observed change in cloud cover, which we argue is more closely tied to the overturning circulation than indirect measurements of SLP at the surface. Our estimates suggest a weakening and eastward shift of the Walker circulation over the last century. Because changes in cloud cover in Atmospheric Model Intercomparison Project simulations forced with increased sea surface temperature are remarkably similar in pattern, sign, and magnitude, we assert that the observed changes in cloud cover and the associated weakening of Walker circulation are at least in part externally forced.

 

http://onlinelibrary.wiley.com/doi/10.1002/2015GL065463/abstract

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Posted
  • Location: Camborne
  • Location: Camborne

The past shows how abrupt climate shifts affect Earth

 

New research shows how past abrupt climatic changes in the North Atlantic propagated globally. The study, led by researchers from Centre for Ice and Climate at the University of Copenhagen's Niels Bohr Institute, shows how interaction between heat transport in the ocean and the atmosphere caused the climatic changes to be expressed in different ways across the Southern Hemisphere. The results shows how forcing the climate system into a different state can trigger climate variations that spread globally and have very different impacts in different regions of Earth. This is important now, where rising atmospheric CO2 levels lead to global warming and may trigger abrupt climatic changes.

Read more at: http://phys.org/news/2015-11-abrupt-climate-shifts-affect-earth.html#jCp

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Posted
  • Location: Ireland, probably South Tipperary
  • Weather Preferences: Cold, Snow, Windstorms and Thunderstorms
  • Location: Ireland, probably South Tipperary

Maximum rates of climate change are systematically underestimated in the geological record

 

Recently observed rates of environmental change are typically much higher than those inferred for the geological past. At the same time, the magnitudes of ancient changes were often substantially greater than those established in recent history. The most pertinent disparity, however, between recent and geological rates is the timespan over which the rates are measured, which typically differ by several orders of magnitude. Here we show that rates of marked temperature changes inferred from proxy data in Earth history scale with measurement timespan as an approximate power law across nearly six orders of magnitude (102 to >107 years). This scaling reveals how climate signals measured in the geological record alias transient variability, even during the most pronounced climatic perturbations of the Phanerozoic. Our findings indicate that the true attainable pace of climate change on timescales of greatest societal relevance is underestimated in geological archives.

 

 

Overview of the article is here http://phys.org/news/2015-11-ancient-climate-underestimated.html

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Posted
  • Location: Camborne
  • Location: Camborne

Sea-level feedback lowers projections of future Antarctic Ice-Sheet mass loss

 

The stability of marine sectors of the Antarctic Ice Sheet (AIS) in a warming climate has been identified as the largest source of uncertainty in projections of future sea-level rise. Sea-level fall near the grounding line of a retreating marine ice sheet has a stabilizing influence on the ice sheets, and previous studies have established the importance of this feedback on ice age AIS evolution. Here we use a coupled ice sheet–sea-level model to investigate the impact of the feedback mechanism on future AIS retreat over centennial and millennial timescales for a range of emission scenarios. We show that the combination of bedrock uplift and sea-surface drop associated with ice-sheet retreat significantly reduces AIS mass loss relative to a simulation without these effects included. Sensitivity analyses show that the stabilization tends to be greatest for lower emission scenarios and Earth models characterized by a thin elastic lithosphere and low-viscosity upper mantle, as is the case for West Antarctica

 

http://www.nature.com/ncomms/2015/151110/ncomms9798/full/ncomms9798.html

 

Discussion

 

http://www.sciencenewsline.com/news/2015111013230012.html

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Posted
  • Location: Camborne
  • Location: Camborne

The potential for snow to supply human water demand in the present and future

 

Runoff from snowmelt is regarded as a vital water source for people and ecosystems throughout the Northern Hemisphere (NH). Numerous studies point to the threat global warming poses to the timing and magnitude of snow accumulation and melt. But analyses focused on snow supply do not show where changes to snowmelt runoff are likely to present the most pressing adaptation challenges, given sub-annual patterns of human water consumption and water availability from rainfall. We identify the NH basins where present spring and summer snowmelt has the greatest potential to supply the human water demand that would otherwise be unmet by instantaneous rainfall runoff. Using a multi-model ensemble of climate change projections, we find that these basins—which together have a present population of ~2 billion people—are exposed to a 67% risk of decreased snow supply this coming century. Further, in the multi-model mean, 68 basins (with a present population of >300 million people) transition from having sufficient rainfall runoff to meet all present human water demand to having insufficient rainfall runoff. However, internal climate variability creates irreducible uncertainty in the projected future trends in snow resource potential, with about 90% of snow-sensitive basins showing potential for either increases or decreases over the near-term decades. Our results emphasize the importance of snow for fulfilling human water demand in many NH basins, and highlight the need to account for the full range of internal climate variability in developing robust climate risk management decisions.

 

Open Access

 

http://iopscience.iop.org/article/10.1088/1748-9326/10/11/114016/meta;jsessionid=290984DF528F1987E4F0CF6CC7E91E19.c3.iopscience.cld.iop.org#

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Posted
  • Location: Camborne
  • Location: Camborne

Southern Ocean buoyancy forcing of ocean ventilation and glacial atmospheric CO2

 

Atmospheric CO2 concentrations over glacial–interglacial cycles closely correspond to Antarctic temperature patterns1. These are distinct from temperature variations in the mid to northern latitudes2, so this suggests that the Southern Ocean is pivotal in controlling natural CO2 concentrations3. Here we assess the sensitivity of atmospheric CO2 concentrations to glacial–interglacial changes in the ocean’s meridional overturning circulation using a circulation model4, 5 for upwelling and eddy transport in the Southern Ocean coupled with a simple biogeochemical description. Under glacial conditions, a broader region of surface buoyancy loss results in upwelling farther to the north, relative to interglacials. The northern location of upwelling results in reduced CO2 outgassing and stronger carbon sequestration in the deep ocean: we calculate that the shift to this glacial-style circulation can draw down 30 to 60 ppm of atmospheric CO2. We therefore suggest that the direct effect of temperatures on Southern Ocean buoyancy forcing, and hence the residual overturning circulation, explains much of the strong correlation between Antarctic temperature variations and atmospheric CO2 concentrations over glacial–interglacial cycles.

 

http://www.nature.com/ngeo/journal/v8/n11/abs/ngeo2538.html

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Posted
  • Location: Ireland, probably South Tipperary
  • Weather Preferences: Cold, Snow, Windstorms and Thunderstorms
  • Location: Ireland, probably South Tipperary

New research finds a major regime shift in the global climate centered in 1987, due to AGW and recovery from the El Chichon eruption.

http://onlinelibrary.wiley.com/doi/10.1111/gcb.13106/abstract

 

Global impacts of the 1980s regime shift

 

Despite evidence from a number of Earth systems that abrupt temporal changes known as regime shifts are important, their nature, scale and mechanisms remain poorly documented and understood. Applying principal component analysis, change-point analysis and a sequential t-test analysis of regime shifts to 72 time series, we confirm that the 1980s regime shift represented a major change in the Earth's biophysical systems from the upper atmosphere to the depths of the ocean and from the Arctic to the Antarctic, and occurred at slightly different times around the world. Using historical climate model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) and statistical modelling of historical temperatures, we then demonstrate that this event was triggered by rapid global warming from anthropogenic plus natural forcing, the latter associated with the recovery from the El Chichón volcanic eruption. The shift in temperature that occurred at this time is hypothesized as the main forcing for a cascade of abrupt environmental changes. Within the context of the last century or more, the 1980s event was unique in terms of its global scope and scale; our observed consequences imply that if unavoidable natural events such as major volcanic eruptions interact with anthropogenic warming unforeseen multiplier effects may occur.

 

 

Review from phys.org: Climate study finds evidence of global shift in the 1980s

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Posted
  • Location: Camborne
  • Location: Camborne

On the definition and identifiability of the alleged “hiatus†in global warming

 

Recent public debate and the scientific literature have frequently cited a “pause†or “hiatus†in global warming. Yet, multiple sources of evidence show that climate change continues unabated, raising questions about the status of the “hiatusâ€. To examine whether the notion of a “hiatus†is justified by the available data, we first document that there are multiple definitions of the “hiatus†in the literature, with its presumed onset spanning a decade. For each of these definitions we compare the associated temperature trend against trends of equivalent length in the entire record of modern global warming. The analysis shows that the “hiatus†trends are encompassed within the overall distribution of observed trends. We next assess the magnitude and significance of all possible trends up to 25 years duration looking backwards from each year over the past 30 years. At every year during the past 30 years, the immediately preceding warming trend was always significant when 17 years (or more) were included in the calculation, alleged “hiatus†periods notwithstanding. If current definitions of the “pause†used in the literature are applied to the historical record, then the climate system “paused†for more than 1/3 of the period during which temperatures rose 0.6 K.

 

Open Access

 

http://www.nature.com/articles/srep16784

 

Discussion

 

http://www.bristol.ac.uk/news/2015/november/no-pause-in-global-warming.html

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Posted
  • Location: Camborne
  • Location: Camborne

Top ten European heatwaves since 1950 and their occurrence in the coming decades

 

The Russian heatwave in 2010 killed tens of thousands of people, and was by far the worst event in Europe since at least 1950, according to recent studies and a novel universal heatwave index capturing both the duration and magnitude of heatwaves. Here, by taking an improved version of this index, namely the heat wave magnitude index daily, we rank the top ten European heatwaves that occurred in the period 1950–2014, and show the spatial distribution of the magnitude of the most recent heatwave in summer 2015. We demonstrate that all these events had a strong impact reported in historical newspapers. We further reveal that the 1972 heatwave in Finland had a comparable spatial extent and magnitude as the European heatwave of 2003, considered the second strongest heatwave of the observational era. In the next two decades (2021–2040), regional climate projections suggest that Europe experiences an enhanced probability for heatwaves comparable to or greater than the magnitude, extent and duration of the Russian heatwave in 2010. We demonstrate that the probability of experiencing a major European heatwave in the coming decades is higher in RCP8.5 than RCP4.5 even though global mean temperature projections do not differ substantially. This calls for a proactive vulnerability assessment in Europe in support of formulating heatwave adaptation strategies to reduce the adverse impacts of heatwaves.

 

Open access

http://iopscience.iop.org/article/10.1088/1748-9326/10/12/124003/meta;jsessionid=DAC5163FB87AB015ABF6D3BB97459011.c3.iopscience.cld.iop.org

 

Press release

 

http://phys.org/news/2015-11-metric-european-strong-decades.html

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Posted
  • Location: Camborne
  • Location: Camborne

Why Europe will soon be cold?

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What is the climate waiting for Russia and Europe in 15-20 years? Will be there weather abnormalities in the coming decades? Will some areas experience more severe winter, while the others will have hot summer? It all depends on how much the climate will be affected by the dynamics of the possible onset of minimum solar magnetic activity. The Sun's behaviour in future cycles is the main theme of a publication on the forecast and explanation of the minima of solar activity. The paper was prepared with contributions from Elena Popova from the Skobeltsyn Institute of Nuclear Physics (Lomonosov Moscow State University) and was published in Scientific Reports.

http://www.eurekalert.org/pub_releases/2015-12/lmsu-wew120115.php

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Posted
  • Location: Camborne
  • Location: Camborne

Study Undercuts Idea That 'Medieval Warm Period' Was Global

Vikings May Not Have Colonized Greenland in Nice Weather

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A new study questions the popular notion that 10th-century Norse people were able to colonize Greenland because of a period of unusually warm weather. Based upon signs left by old glaciers, researchers say the climate was already cold when the Norse arrived—and that climate thus probably played little role in their mysterious demise some 400 years later. On a larger scale, the study adds to building evidence that the so-called Medieval Warm Period, when Europe enjoyed exceptionally clement weather, did not necessarily extend to other parts of the world.

http://earth.columbia.edu/articles/view/3266

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Posted
  • Location: Camborne
  • Location: Camborne

Humidity trends imply increased sensitivity to clouds in a warming Arctic

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Infrared radiative processes are implicated in Arctic warming and sea-ice decline. The infrared cloud radiative effect (CRE) at the surface is modulated by cloud properties; however, CRE also depends on humidity because clouds emit at wavelengths that are semi-transparent to greenhouse gases, most notably water vapour. Here we show how temperature and humidity control CRE through competing influences between the mid- and far-infrared. At constant relative humidity, CRE does not decrease with increasing temperature/absolute humidity as expected, but rather is found to be approximately constant for temperatures characteristic of the Arctic. This stability is disrupted if relative humidity varies. Our findings explain observed seasonal and regional variability in Arctic CRE of order 10Wm−2. With the physical properties of Arctic clouds held constant, we calculate recent increases in CRE of 1–5Wm−2 in autumn and winter, which are projected to reach 5–15Wm−2 by 2050, implying increased sensitivity of the surface to clouds.

http://www.nature.com/ncomms/2015/151210/ncomms10117/full/ncomms10117.html

Article

http://www.sciencedaily.com/releases/2015/12/151210091851.htm

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Posted
  • Location: Camborne
  • Location: Camborne

Quote Kate Marvel

I'm sorry but climate sensitivity might be higher than we thought

Implications for climate sensitivity from the response to individual forcings

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Climate sensitivity to doubled CO2 is a widely used metric for the large-scale response to external forcing. Climate models predict a wide range for two commonly used definitions: the transient climate response (TCR: the warming after 70 years of CO2 concentrations that rise at 1% per year), and the equilibrium climate sensitivity (ECS: the equilibrium temperature change following a doubling of CO2 concentrations). Many observational data sets have been used to constrain these values, including temperature trends over the recent past1, 2, 3, 4, 5, 6, inferences from palaeoclimate7, 8 and process-based constraints from the modern satellite era9, 10. However, as the IPCC recently reported11, different classes of observational constraints produce somewhat incongruent ranges. Here we show that climate sensitivity estimates derived from recent observations must account for the efficacy of each forcing active during the historical period. When we use single-forcing experiments to estimate these efficacies and calculate climate sensitivity from the observed twentieth-century warming, our estimates of both TCR and ECS are revised upwards compared to previous studies, improving the consistency with independent constraints.

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2888.html#close

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Posted
  • Location: Camborne
  • Location: Camborne

Warmer air and sea, declining ice continue to trigger Arctic change

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A new NOAA-sponsored report shows that air temperature in 2015 across the Arctic was well above average with temperature anomalies over land more than 2 degrees Fahrenheit above average, the highest since records began in 1900. Increasing air and sea surface temperatures, decreasing sea ice extent and Greenland ice sheet mass, and changing behavior of fish and walrus are among key observations released today in the Arctic Report Card 2015.

http://www.eurekalert.org/pub_releases/2015-12/nh-waa121415.php

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Posted
  • Location: Camborne
  • Location: Camborne

Text-mining the signals of climate change doubt http://www.sciencedirect.com/science/articl

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Abstract

Climate scientists overwhelmingly agree that the Earth is getting warmer and that the rise in average global temperature is predominantly due to human activity. Yet a significant proportion of the American public, as well as a considerable number of legislators in the U.S. Congress, continue to reject the “consensus view.” While the source of the disagreement is varied, one prominent explanation centres on the activities of a coordinated and well-funded countermovement of climate sceptics. This study contributes to the literature on organized climate scepticism by providing the first systematic overview of conservative think tank sceptical discourse in nearly 15 years. Specifically, we (1) compile the largest corpus of contrarian literature to date, collecting over 16,000 documents from 19 organizations over the period 1998–2013; (2) introduce a methodology to measure key themes in the corpus which scales to the substantial increase in content generated by conservative think tanks over the past decade; and (3) leverage this new methodology to shed light on the relative prevalence of science- and policy-related discussion among conservative think tanks. We find little support for the claim that “the era of science denial is over”—instead, discussion of climate science has generally increased over the sample period.

 

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