New Research

[knocker]

Early deglacial Atlantic overturning decline and its role in atmospheric CO₂ rise inferred from carbon isotopes (δ¹³C)

 

Abstract. The reason for the initial rise in atmospheric CO₂ during the last deglaciation remains unknown. Most recent hypotheses invoke Southern Hemisphere processes such as shifts in midlatitude westerly winds. Coeval changes in the Atlantic meridional overturning circulation (AMOC) are poorly quantified, and their relation to the CO₂ increase is not understood. Here we compare simulations from a global, coupled climate–biogeochemistry model that includes a detailed representation of stable carbon isotopes (δ¹³C) with a synthesis of high-resolution δ¹³C reconstructions from deep-sea sediments and ice core data. In response to a prolonged AMOC shutdown initialized from a preindustrial state, modeled δ¹³C of dissolved inorganic carbon (δ¹³C_DIC) decreases in most of the surface ocean and the subsurface Atlantic, with largest amplitudes (more than 1.5‰) in the intermediate-depth North Atlantic. It increases in the intermediate and abyssal South Atlantic, as well as in the subsurface Southern, Indian, and Pacific oceans. The modeled pattern is similar and highly correlated with the available foraminiferal δ¹³C reconstructions spanning from the late Last Glacial Maximum (LGM, ~19.5–18.5 ka BP) to the late Heinrich stadial event 1 (HS1, ~16.5–15.5 ka BP), but the model overestimates δ¹³C_DIC reductions in the North Atlantic. Possible reasons for the model–sediment-data differences are discussed. Changes in remineralized δ¹³C_DIC dominate the total δ¹³C_DIC variations in the model but preformed contributions are not negligible. Simulated changes in atmospheric CO₂ and its isotopic composition (δ¹³C_CO2) agree well with ice core data. Modeled effects of AMOC-induced wind changes on the carbon and isotope cycles are small, suggesting that Southern Hemisphere westerly wind effects may have been less important for the global carbon cycle response during HS1 than previously thought. Our results indicate that during the early deglaciation the AMOC decreased for several thousand years. We propose that the observed early deglacial rise in atmospheric CO₂ and the decrease in δ¹³C_CO2 may have been dominated by an AMOC-induced decline of the ocean's biologically sequestered carbon storage.

 

http://www.clim-past.net/11/135/2015/cp-11-135-2015.pdf

[knocker]

Researchers find new evidence of warming

 

A study of three remote lakes in Ecuador led by Queen's University researchers has revealed the vulnerability of tropical high mountain lakes to global climate change - the first study of its kind to show this. The data explains how the lakes are changing due to the water warming as the result of climate change.

Read more at: http://phys.org/news/2015-02-evidence.html#jCp

[knocker]

Causes of Strengthening and Weakening of ENSO Amplitude under Global Warming in Four CMIP5 Models

 

Abstract

The mechanisms for El Niño-Southern Oscillation (ENSO) amplitude change under global warming are investigated through quantitative assessment of air-sea feedback processes in present-day and future climate simulations of four models participating in the fifth Coupled Models Inter-comparison Project (CMIP5). Two models (MPI-ESM-MR and MRI-CGCM) project strengthened ENSO amplitude, whereas the other two models (NCAR-CCSM4 and FGOALS-g2) project weakened ENSO amplitude. A mixed-layer heat budget diagnosis shows that the major cause of the projected ENSO amplitude difference between the two groups are attributed to the changes of the thermocline and zonal advective feedbacks. A weaker (stronger) equatorial thermocline response to a unit anomalous zonal wind stress forcing in the Niño4 region is found in NCAR-CCSM4 and FGOALS-g2 (MPI-ESM-MR and MRI-CGCM). The cause of the different response arises from the change in the meridional scale of ENSO. A narrower (wider) meridional width of sea surface temperature (SST) and zonal wind stress narrower (wider) meridional width of sea surface temperature (SST) and zonal wind stress anomalies causes a strengthening (weakening) of the equatorial thermocline response and thus stronger Bjerknes and zonal advective feedbacks, as the subsurface temperature and zonal current anomalies depend on the thermocline response. Consequently, the ENSO amplitude increases (decreases). The change of ENSO meridional width is caused by the change in mean meridional overturning circulation in the equatorial Pacific ocean, which depends on change of mean wind stress and SST warming patterns under global warming.

 

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00439.1?utm_content=buffer2f30e&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

[Gray-Wolf]

http://news.sciencemag.org/earth/2015/02/smoke-distant-fires-could-create-more-deadly-tornadoes

 

So in a world of increasing wildfires are we to expect fiercer tornados? 

[knocker]

Study shows global sea ice diminishing, despite Antarctic gains

 

Sea ice increases in Antarctica do not make up for the accelerated Arctic sea ice loss of the last decades, a new NASA study finds. As a whole, the planet has been shedding sea ice at an average annual rate of 13,500 square miles (35,000 square kilometers) since 1979, the equivalent of losing an area of sea ice larger than the state of Maryland every year.

Read more at: http://phys.org/news/2015-02-global-sea-ice-diminishing-antarctic.html#jCp

[knocker]

Rapid disappearance of perennial ice on Canada's most northern lake

 

Abstract

Field records, aerial photographs and satellite imagery show that the perennial ice cover on Ward Hunt Lake at Canada's northern coast experienced rapid contraction and thinning after at least 50 years of relative stability. On all dates of sampling from 1953 to 2007, 3.5 to 4.3 m of perennial ice covered 65-85 % of the lake surface in summer. The ice cover thinned from 2008 onwards, and the lake became ice-free in 2011, an event followed by 26 days of open-water conditions in 2012. This rapid ice loss corresponded to a significant increase in melting degree days (MDD), from a mean (±SD) of 80.4 (±36.5) MDD (1996-2007) to 136.2 (±16.4) MDD (2008-2012). The shallow bathymetry combined with heat advection by warm inflows caused feedback effects that accelerated the ice decay. These observations show how changes across a critical threshold can result in the rapid disappearance of thick perennial ice.

 

http://onlinelibrary.wiley.com/doi/10.1002/2014GL062960/abstract?utm_content=buffer22ebb&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

[knocker]

Monster hurricanes reached US Northeast during prehistoric periods of ocean warming

 

WASHINGTON, D.C. - Intense hurricanes possibly more powerful than any storms New England has experienced in recorded history frequently pounded the region during the first millennium, from the peak of the Roman Empire into the height of the Middle Ages, according to a new study. The findings could have implications for the intensity and frequency of hurricanes that the U.S. East and Gulf coasts could experience as ocean temperatures increase as a result of climate change, according to the study's authors.

 

http://www.eurekalert.org/pub_releases/2015-02/agu-mhr021115.php

[knocker]

Unprecedented 21st century drought risk in the American Southwest and Central Plains

 

Abstract

In the Southwest and Central Plains of Western North America, climate change is expected to increase drought severity in the coming decades. These regions nevertheless experienced extended Medieval-era droughts that were more persistent than any historical event, providing crucial targets in the paleoclimate record for benchmarking the severity of future drought risks. We use an empirical drought reconstruction and three soil moisture metrics from 17 state-of-the-art general circulation models to show that these models project significantly drier conditions in the later half of the 21st century compared to the 20th century and earlier paleoclimatic intervals. This desiccation is consistent across most of the models and moisture balance variables, indicating a coherent and robust drying response to warming despite the diversity of models and metrics analyzed. Notably, future drought risk will likely exceed even the driest centuries of the Medieval Climate Anomaly (1100–1300 CE) in both moderate (RCP 4.5) and high (RCP 8.5) future emissions scenarios, leading to unprecedented drought conditions during the last millennium.

 

 

http://advances.sciencemag.org/content/1/1/e1400082 (Open Access)

[knocker]

Carbon release from ocean helped end the Ice Age

 

Published today in Nature, the study shows that carbon stored in an isolated reservoir deep in the Southern Ocean re-connected with the atmosphere, driving a rise in atmospheric CO2 and an increase in global temperatures. The finding gives scientists an insight into how the ocean affects the carbon cycle and climate change.

 

http://www.eurekalert.org/pub_releases/2015-02/uadb-crf021115.php

[knocker]

Ice streams in the Laurentide Ice Sheet: Identification, characteristics and comparison to modern ice sheets

 

Abstract

This paper presents a comprehensive review and synthesis of ice streams in the Laurentide Ice Sheet (LIS) based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed. The inventory includes 117 ice streams, which have been identified based on a variety of evidence including their bedform imprint, large-scale geomorphology/topography, till properties, and ice rafted debris in ocean sediment records. Despite uncertainty in identifying ice streams in hard bedrock areas, it is unlikely that any major ice streams have been missed. During the Last Glacial Maximum, Laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets. Large ice streams had extensive onset zones and were fed by multiple tributaries and, where ice drained through regions of high relief, the spacing of ice streams shows a degree of spatial self-organisation which has hitherto not been recognised. Topography exerted a primary control on the location of ice streams, but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock, and where networks of ice streams switched direction repeatedly and probably over short time scales. As the ice sheet retreated onto its low relief interior, several ice streams show no correspondence with topography or underlying geology, perhaps facilitated by localised build-up of pressurised subglacial meltwater. They differed from most other ice stream tracks in having much lower length-to-width ratios and have no modern analogues. There have been very few attempts to date the initiation and cessation of ice streams, but it is clear that ice streams switched on and off during deglaciation, rather than maintaining the same trajectory as the ice margin retreated. We provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30% of the margin was drained by ice streams at the LGM (similar to that for present day Antarctic ice sheets), but this decreases to 15% and 12% at 12 cal ka BP and 10 cal ka BP, respectively. The extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate, or internal ice dynamical feedbacks unrelated to climate (or both) is largely unknown and represents a key area for future work to address.

 

http://www.sciencedirect.com/science/article/pii/S0012825215000203

[knocker]

Atmospheric impacts of sea ice decline in CO2 induced global warming

 

Abstract

Changes in sea ice cover have important consequences for both Earth’s energy budget and atmospheric dynamics. Sea ice acts as a positive feedback in the climate system, amplifying effects of radiative forcing while also affecting the meridional and interhemispheric temperature gradients that can impact mid- and low latitude atmospheric circulation. In this study, we partition and evaluate the effects of changing sea ice cover on global warming using a set of simulations with active and suppressed sea ice response. Two aspects of CO2-induced sea ice changes are investigated: (1) the effect of changing sea ice cover on global and local temperature changes; and (2) the impact of sea ice loss on atmospheric circulation and extreme weather events. We find that in the absence of sea ice decline, global temperature response decreases by 21–37 %, depending on the sea ice treatment and the CO2 forcing applied. Weakened global warming in the absence of changes in sea ice cover is not only due to a decreased high latitude warming but is also a consequence of a weaker tropical warming. In the northern midlatitudes, sea ice decline affects the magnitude and sign of zonal wind response to global warming in the winter and autumn seasons. Presence or absence of sea ice cover impacts the intensity and frequency of winter extreme precipitation and temperature events (temperature minima, number of heavy precipitation days and number of ice days). For some of the analyzed extreme weather indices, the difference between the responses with and without sea ice decline is eliminated when taking into account the amplifying effect of sea ice loss on hemispheric warming. However, in other cases, we find the influence of higher order factors, exerting weaker but opposing effects than those expected from the global temperature increase.

 

http://dge.stanford.edu/labs/caldeiralab/Caldeira_research/Cvijanovic_SeaIce.html

[knocker]

An extreme event of sea-level rise along the Northeast coast of North America in 2009–2010

 

The coastal sea levels along the Northeast Coast of North America show significant year-to-year fluctuations in a general upward trend. The analysis of long-term tide gauge records identified an extreme sea-level rise (SLR) event during 2009–10. Within this 2-year period, the coastal sea level north of New York City jumped by 128 mm. This magnitude of interannual SLR is unprecedented (a 1-in-850 year event) during the entire history of the tide gauge records. Here we show that this extreme SLR event is a combined effect of two factors: an observed 30% downturn of the Atlantic meridional overturning circulation during 2009–10, and a significant negative North Atlantic Oscillation index. The extreme nature of the 2009–10 SLR event suggests that such a significant downturn of the Atlantic overturning circulation is very unusual. During the twenty-first century, climate models project an increase in magnitude and frequency of extreme interannual SLR events along this densely populated coast.

 

http://www.nature.com/ncomms/2015/150224/ncomms7346/full/ncomms7346.html

 

BBC article

 

http://www.bbc.co.uk/news/science-environment-31604953

[knocker]

Observational determination of surface radiative forcing by CO₂ from 2000 to 2010

 

The climatic impact of CO₂ and other greenhouse gases is usually quantified in terms of radiative forcing¹, calculated as the difference between estimates of the Earth’s radiation field from pre-industrial and present-day concentrations of these gases. Radiative transfer models calculate that the increase in CO₂ since 1750 corresponds to a global annual-mean radiative forcing at the tropopause of 1.82 Â± 0.19 W m^−2 (ref. 2). However, despite widespread scientific discussion and modelling of the climate impacts of well-mixed greenhouse gases, there is little direct observational evidence of the radiative impact of increasing atmospheric CO₂. Here we present observationally based evidence of clear-sky CO₂ surface radiative forcing that is directly attributable to the increase, between 2000 and 2010, of 22 parts per million atmospheric CO₂. The time series of this forcing at the two locations—the Southern Great Plains and the North Slope of Alaska—are derived from Atmospheric Emitted Radiance Interferometer spectra³ together with ancillary measurements and thoroughly corroborated radiative transfer calculations⁴. The time series both show statistically significant trends of 0.2 W m^−2 per decade (with respective uncertainties of ±0.06 W m^−2 per decade and ±0.07 W m^−2 per decade) and have seasonal ranges of 0.1–0.2 W m^−2. This is approximately ten per cent of the trend in downwelling longwave radiation^{5, 6, 7}. These results confirm theoretical predictions of the atmospheric greenhouse effect due to anthropogenic emissions, and provide empirical evidence of how rising CO₂ levels, mediated by temporal variations due to photosynthesis and respiration, are affecting the surface energy balance.

 

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14240.html#close

[knocker]

IPCC sea-level rise scenarios not fit for purpose for high-risk coastal areas

 

The sea-level rise scenarios of the Intergovernmental Panel on Climate Change (IPCC) do not necessarily provide the right information for high-risk coastal decision-making and management, according to new research involving scientists from the University of Southampton.

 

http://www.eurekalert.org/pub_releases/2015-02/uos-isr022615.php

[knocker]

Full press release for the paper one up

 

First Direct Observation of Carbon Dioxide’s Increasing Greenhouse Effect at the Earth’s Surface

http://newscenter.lbl.gov/2015/02/25/co2-greenhouse-effect-increase/

[knocker]

Atlantic and Pacific multidecadal oscillations and Northern Hemisphere temperatures

 

The recent slowdown in global warming has brought into question the reliability of climate model projections of future temperature change and has led to a vigorous debate over whether this slowdown is the result of naturally occurring, internal variability or forcing external to Earth’s climate system. To address these issues, we applied a semi-empirical approach that combines climate observations and model simulations to estimate Atlantic- and Pacific-based internal multidecadal variability (termed “AMO†and “PMO,†respectively). Using this method, the AMO and PMO are found to explain a large proportion of internal variability in Northern Hemisphere mean temperatures. Competition between a modest positive peak in the AMO and a substantially negative-trending PMO are seen to produce a slowdown or “false pause†in warming of the past decade.

 

http://www.sciencemag.org/content/347/6225/988.short

[keithlucky]

Full press release for the paper one up

 

First Direct Observation of Carbon Dioxide’s Increasing Greenhouse Effect at the Earth’s Surface

http://newscenter.lbl.gov/2015/02/25/co2-greenhouse-effect-increase/

http://hockeyschtick.blogspot.com/2015/02/why-new-paper-does-not-provide-evidence.html

[knocker]

ERA-20CM: a twentieth century atmospheric model ensemble

 

This paper describes an ensemble of ten atmospheric model integrations for the years 1899 to 2010, performed at the European Centre for Medium-Range Weather Forecasts (ECMWF). Horizontal spectral resolution is T159 (about 125 km), using 91 levels in the vertical from the surface up to 1 Pa, and a time step of one hour. This ensemble, denoted by ERA-20CM, formed the first step toward a 20^th century reanalysis within ERA-CLIM, a three-year European funded project involving nine partners.

Sea-surface temperature and sea-ice cover are prescribed by an ensemble of realizations (HadISST2), as recently produced by the Met Office Hadley Centre within ERA-CLIM. Variation in these realizations reflect uncertainties in the available observational sources on which this product is based. Forcing terms in the model radiation scheme follow CMIP5 recommendations. Any effect of their uncertainty is neglected. These terms include solar forcing, greenhouse gases, ozone and aerosols. Both the ocean-surface and radiative forcing incorporate a proper long-term evolution of climate trends in the 20th century, and the occurrence of major events, such as the El Niño-Southern Oscillations and volcanic eruptions.

No atmospheric observations were assimilated. For this reason ERA-20CM is not able to reproduce actual synoptic situations. The ensemble is, however, able to provide a statistical estimate of the climate. Overall, the temperature rise over land is in fair agreement with the CRUTEM4 observational product. Over the last two decades the warming over land exceeds the warming over sea, which is consistent with models participating in the CMIP5 project, as well with the ECMWF ERA-Interim reanalysis. Some aspects of warming and of the hydrological cycle are discerned, and the model response to volcanic eruptions is qualitatively correct.

The data from ERA-20CM are freely available, embracing monthly-mean fields for many atmospheric and ocean-wave quantities, and synoptic fields for a small, essential subset.

 

http://onlinelibrary.wiley.com/doi/10.1002/qj.2528/abstract

[knocker]

Not much good news lately

 

Combined Arctic ice observations show decades of loss

 

It's no surprise that Arctic sea ice is thinning. What is new is just how long, how steadily, and how much it has declined. University of Washington researchers compiled modern and historic measurements to get a full picture of how Arctic sea ice thickness has changed.

 

The results, published in The Cryosphere, show a thinning in the central Arctic Ocean of 65 percent between 1975 and 2012. September ice thickness, when the ice cover is at a minimum, is 85 percent thinner for the same 37-year stretch.

 

http://www.eurekalert.org/pub_releases/2015-03/uow-cai030215.php

 

Arctic sea ice thickness loss determined using subsurface, aircraft, and satellite observations

 

Abstract. Sea ice thickness is a fundamental climate state variable that provides an integrated measure of changes in the high-latitude energy balance. However, observations of mean ice thickness have been sparse in time and space, making the construction of observation-based time series difficult. Moreover, different groups use a variety of methods and processing procedures to measure ice thickness, and each observational source likely has different and poorly characterized measurement and sampling errors. Observational sources used in this study include upward-looking sonars mounted on submarines or moorings, electromagnetic sensors on helicopters or aircraft, and lidar or radar altimeters on airplanes or satellites. Here we use a curve-fitting approach to determine the large-scale spatial and temporal variability of the ice thickness as well as the mean differences between the observation systems, using over 3000 estimates of the ice thickness. The thickness estimates are measured over spatial scales of approximately 50 km or time scales of 1 month, and the primary time period analyzed is 2000–2012 when the modern mix of observations is available. Good agreement is found between five of the systems, within 0.15 m, while systematic differences of up to 0.5 m are found for three others compared to the five. The trend in annual mean ice thickness over the Arctic Basin is −0.58 ± 0.07 m decade^−1 over the period 2000–2012. Applying our method to the period 1975–2012 for the central Arctic Basin where we have sufficient data (the SCICEX box), we find that the annual mean ice thickness has decreased from 3.59 m in 1975 to 1.25 m in 2012, a 65% reduction. This is nearly double the 36% decline reported by an earlier study. These results provide additional direct observational evidence of substantial sea ice losses found in model analyses.

 

http://www.the-cryosphere.net/9/269/2015/tc-9-269-2015.pdf

Edited March 3, 2015 by knocker

[knocker]

New Models Yield Clearer Picture of Emissions' True Costs

 

DURHAM, N.C. - When its environmental and human health toll is factored in, a gallon of gasoline costs us about $3.80 more than the pump price, a new Duke University study finds.

 

The social cost of a gallon of diesel is about $4.80 more than the pump price; the price of natural gas more than doubles; and coal-fired electricity more than quadruples. Solar and wind power, on the other hand, become cheaper than they initially seem.

 

"We think we know what the prices of fossil fuels are, but their impacts on climate and human health are much larger than previously realized," said Drew T. Shindell, professor of climate sciences at Duke's Nicholas School of the Environment. "We're making decisions based on misleading costs."

 

http://nicholas.duke.edu/news/new-models-yield-clearer-picture-emissions-true-costs

[knocker]

I obviously haven't as yet read this thoroughly but at first glance looks extremely interesting.

 

Arctic climate change in an ensemble of regional CORDEX simulations

 

Abstract

Fifth phase Climate Model Intercomparison Project historical and scenario simulations from four global climate models (GCMs) using the Representative Concentration Pathways greenhouse gas concentration trajectories RCP4.5 and RCP8.5 are downscaled over the Arctic with the regional Rossby Centre Atmosphere model (RCA). The regional model simulations largely reflect the circulation bias patterns of the driving global models in the historical period, indicating the importance of lateral and lower boundary conditions. However, local differences occur as a reduced winter 2-m air temperature bias over the Arctic Ocean and increased cold biases over land areas in RCA. The projected changes are dominated by a strong warming in the Arctic, exceeding 15°K in autumn and winter over the Arctic Ocean in RCP8.5, strongly increased precipitation and reduced sea-level pressure. Near-surface temperature and precipitation are linearly related in the Arctic. The wintertime inversion strength is reduced, leading to a less stable stratification of the Arctic atmosphere. The diurnal temperature range is reduced in all seasons. The large-scale change patterns are dominated by the surface and lateral boundary conditions so future response is similar in RCA and the driving global models. However, the warming over the Arctic Ocean is smaller in RCA; the warming over land is larger in winter and spring but smaller in summer. The future response of winter cloud cover is opposite in RCA and the GCMs. Precipitation changes in RCA are much larger during summer than in the global models and more small-scale change patterns occur.

 

http://www.polarresearch.net/index.php/polar/article/view/24603?utm_source=twitterfeed&utm_medium=twitter&utm_campaign=Feed%3A+Cryonews+%28CryoNews%29

Edited March 9, 2015 by knocker

[knocker]

The weakening summer circulation in the Northern Hemisphere mid-latitudes

 

Rapid warming in the Arctic could influence mid-latitude circulation by reducing the poleward temperature gradient. The largest changes are generally expected in autumn or winter but whether significant changes have occurred is debated. Here we report significant weakening of summer circulation detected in three key dynamical quantities: (i) the zonal-mean zonal wind, (ii) the eddy kinetic energy (EKE) and (iii) the amplitude of fast-moving Rossby waves. Weakening of the zonal wind is explained by a reduction in poleward temperature gradient. Changes in Rossby waves and EKE are consistent with regression analyses of climate model projections and changes over the seasonal cycle. Monthly heat extremes are associated with low EKE and thus the observed weakening might have contributed to more persistent heat waves in recent summers.

 

http://www.sciencemag.org/content/early/2015/03/13/science.1261768

 

Article

 

http://www.newscientist.com/article/dn27150-warming-arctic-blamed-for-worsening-summer-heatwaves.html#.VQQbPo42fPT

[knocker]

Forcing, feedback and internal variability in global temperature trends

 

Most present-generation climate models simulate an increase in global-mean surface temperature (GMST) since 1998, whereas observations suggest a warming hiatus. It is unclear to what extent this mismatch is caused by incorrect model forcing, by incorrect model response to forcing or by random factors. Here we analyse simulations and observations of GMST from 1900 to 2012, and show that the distribution of simulated 15-year trends shows no systematic bias against the observations. Using a multiple regression approach that is physically motivated by surface energy balance, we isolate the impact of radiative forcing, climate feedback and ocean heat uptake on GMST—with the regression residual interpreted as internal variability—and assess all possible 15- and 62-year trends. The differences between simulated and observed trends are dominated by random internal variability over the shorter timescale and by variations in the radiative forcings used to drive models over the longer timescale. For either trend length, spread in simulated climate feedback leaves no traceable imprint on GMST trends or, consequently, on the difference between simulations and observations. The claim that climate models systematically overestimate the response to radiative forcing from increasing greenhouse gas concentrations therefore seems to be unfounded.

 

http://www.nature.com/nature/journal/v517/n7536/pdf/nature14117.pdf

[knocker]

Multi-Scale Entropy Analysis as a Method for Time-Series Analysis of Climate Data

 

Abstract: Evidence is mounting that the temporal dynamics of the climate system are changing at the same time as the average global temperature is increasing due to multiple climate forcings. A large number of extreme weather events such as prolonged cold spells, heatwaves, droughts and floods have been recorded around the world in the past 10 years. Such changes in the temporal scaling behaviour of climate time-series data can be difficult to detect. While there are easy and direct ways of analysing climate data by calculating the means and variances for different levels of temporal aggregation, these methods can miss more subtle changes in their dynamics. This paper describes multi-scale entropy (MSE) analysis as a tool to study climate time-series data and to identify temporal scales of variability and their change over time in climate time-series. MSE estimates the sample entropy of the time-series after coarse-graining at different temporal scales. An application of MSE to Central European, variance-adjusted, mean monthly air temperature anomalies (CRUTEM4v) is provided. The results show that the temporal scales of the current climate (1960–2014) are different from the long-term average (1850–1960). For temporal scale factors longer than 12 months, the sample entropy increased markedly compared to the long-term record. Such an increase can be explained by systems theory with greater complexity in the regional temperature data. From 1961 the patterns of monthly air temperatures are less regular at time-scales greater than 12 months than in the earlier time period. This finding suggests that, at these inter-annual time scales, the temperature variability has become less predictable than in the past. It is possible that climate system feedbacks are expressed in altered temporal scales of the European temperature time-series data. A comparison with the variance and Shannon entropy shows that MSE analysis can provide additional information on the statistical properties of climate time-series data that can go undetected using traditional methods.

 

http://www.mdpi.com/2225-1154/3/1/227 (open access)

 

Synopsis

 

http://www.eurekalert.org/pub_releases/2015-03/uol-rt031615.php

[knocker]

Interesting although I suspect the title of the article could have been better

 

International study raises questions about cause of global ice ages

 

HANOVER, N.H. - A new international study casts doubt on the leading theory of what causes ice ages around the world -- changes in the way the Earth orbits the sun.

The researchers found that glacier movement in the Southern Hemisphere is influenced primarily by sea surface temperature and atmospheric carbon dioxide rather than changes in the Earth's orbit, which are thought to drive the advance and retreat of ice sheets in the Northern Hemisphere.

 

http://www.eurekalert.org/pub_releases/2015-03/dc-isr032015.php