Gottschalk J.,University of Cambridge |
Skinner L.C.,University of Cambridge |
Misra S.,University of Cambridge |
Waelbroeck C.,LSCE |
And 2 more authors.
Nature Geoscience | Year: 2015
The glacial climate system transitioned rapidly between cold (stadial) and warm (interstadial) conditions in the Northern Hemisphere. This variability, referred to as Dansgaard-Oeschger variability, is widely believed to arise from perturbations of the Atlantic Meridional Overturning Circulation. Evidence for such changes during the longer Heinrich stadials has been identified, but direct evidence for overturning circulation changes during Dansgaard-Oeschger events has proven elusive. Here we reconstruct bottom water [CO3 2-[ variability from B/Ca ratios of benthic foraminifera and indicators of sedimentary dissolution, and use these reconstructions to infer the flow of northern-sourced deep water to the deep central sub-Antarctic Atlantic Ocean. We find that nearly every Dansgaard-Oeschger interstadial is accompanied by a rapid incursion of North Atlantic Deep Water into the deep South Atlantic. Based on these results and transient climate model simulations, we conclude that North Atlantic stadial-interstadial climate variability was associated with significant Atlantic overturning circulation changes that were rapidly transmitted across the Atlantic. However, by demonstrating the persistent role of Atlantic overturning circulation changes in past abrupt climate variability, our reconstructions of carbonate chemistry further indicate that the carbon cycle response to abrupt climate change was not a simple function of North Atlantic overturning. © 2015 Macmillan Publishers Limited.
News Article | December 12, 2016
PARIS (Reuters) - Global methane emissions from agriculture and other sources have surged in recent years, threatening efforts to slow climate change, an international study has found. Researchers led by French Laboratoire des Sciences du Climat et de l'Environnement (LSCE) reported that methane concentrations in the air began to surge around 2007 and grew precipitously in 2014 and 2015. In that two-year period methane concentrations shot up by 10 or more parts per billion (ppb) annually, compared with an average annual increase of only 0.5 ppb during the early 2000s, according to the study released by the Global Carbon Project, which groups climate researchers. Marielle Saunois, lead author of the study and assistant professor at Université de Versailles Saint Quentin, said that the increase in methane emissions could threaten efforts to limit global warming. "We should do more about methane emissions. If we want to stay below a 2 degrees (Celsius) temperature increase, we should not follow this track and need to make a rapid turnaround," she said in a statement. Methane is much less prevalent in the atmosphere than carbon dioxide (CO2) -- the main man-made greenhouse gas -- but is more potent because it traps 28 times more heat. The report did not say to what extent methane contributes to global warming. CO2 emissions are expected to remain flat for the third year in a row in 2016, thanks to falls in China, the Global Carbon Project said last month. Saunois said that while the reasons behind the methane surge are not well understood, the most likely sources are cattle ranching and rice farming. Cows expel large quantities of methane and the flooded soils of rice paddies are homes for microbes that produce the gas. She cited data from the United Nations' Food and Agriculture Organization indicating that livestock operations worldwide expanded from producing 1.3 billion head of cattle in 1994 to nearly 1.5 billion in 2014, with a similar increase in rice cultivation in many Asian countries. Robert Jackson, a co-author of the paper and Professor in Earth System Science at Stanford University, said that methane can come from many different sources, including natural sources such as marshes and other wetlands, but about 60 percent comes from human activities, notably agriculture. A smaller portion of the human contribution, about a third, comes from fossil fuel exploration, where methane can leak from oil and gas wells during drilling. "When it comes to methane, there has been a lot of focus on the fossil fuel industry, but we need to look just as hard, if not harder, at agriculture," Jackson said.
Lippold J.,University of Heidelberg |
Gherardi J.-M.,LSCE |
Gherardi J.-M.,University of Bergen |
Luo Y.,University of British Columbia
Geophysical Research Letters | Year: 2011
Variations of the Atlantic Meridional Overturning Circulation (AMOC) are believed to have crucially influenced Earth's climate due to its key role in the inter-hemispheric redistribution of heat and carbon. To assess its past strength, the sedimentary 231Pa/230Th proxy has been developed and improved but also contested due to its sensitivity to other factors beyond ocean circulation. In order to provide a better basis for the understanding of the Atlantic 231Pa/230Th system, and therefore to shed light on the controversy, we compare new measurements of Holocene sediments from the north Brazilian margin to water column data and the output of a two-dimensional scavenging-circulation model, based on modern circulation patterns and reversible scavenging parameters. We show that sedimentary 231Pa/230Th data from one specific area of the Atlantic are in very good agreement with model results suggesting that sedimentary 231Pa/230Th is predominantly driven by the AMOC. Therefore, 231Pa/230Th represents an appropriate method to reconstruct past AMOC at least qualitatively along the western margin. © 2011 by the American Geophysical Union.
Cattiaux J.,LSCE |
Vautard R.,LSCE |
Cassou C.,European Center for Research and Advanced Training in Scientific Computation |
Yiou P.,LSCE |
And 2 more authors.
Geophysical Research Letters | Year: 2010
The winter of 2009/2010 was characterized by record persistence of the negative phase of the North-Atlantic Oscillation (NAO) which caused several severe cold spells over Northern and Western Europe. This somehow unusual winter with respect to the most recent ones arose concurrently with public debate on climate change, during and after the Copenhagen climate negotiations. We show however that the cold European temperature anomaly of winter 2010 was (i) not extreme relative to winters of the past six decades, and (ii) warmer than expected from its record-breaking seasonal circulation indices such as NAO or blocking frequency. Daily flow-analogues of winter 2010, taken in past winters, were associated with much colder temperatures. The winter 2010 thus provides a consistent picture of a regional cold event mitigated by long-term climate warming. © 2010 by the American Geophysical Union.
Yao T.,CAS Institute of Tibetan Plateau Research |
Yao T.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute |
Masson-Delmotte V.,LSCE |
Gao J.,CAS Institute of Tibetan Plateau Research |
And 13 more authors.
Reviews of Geophysics | Year: 2013
The stable oxygen isotope ratio (δ18O) in precipitation is an integrated tracer of atmospheric processes worldwide. Since the 1990s, an intensive effort has been dedicated to studying precipitation isotopic composition at more than 20 stations in the Tibetan Plateau (TP) located at the convergence of air masses between the westerlies and Indian monsoon. In this paper, we establish a database of precipitation δ18O and use different models to evaluate the climatic controls of precipitation δ18O over the TP. The spatial and temporal patterns of precipitation δ18O and their relationships with temperature and precipitation reveal three distinct domains, respectively associated with the influence of the westerlies (northern TP), Indian monsoon (southern TP), and transition in between. Precipitation δ18O in the monsoon domain experiences an abrupt decrease in May and most depletion in August, attributable to the shifting moisture origin between Bay of Bengal (BOB) and southern Indian Ocean. High-resolution atmospheric models capture the spatial and temporal patterns of precipitation δ18O and their relationships with moisture transport from the westerlies and Indian monsoon. Only in the westerlies domain are atmospheric models able to represent the relationships between climate and precipitation δ18O. More significant temperature effect exists when either the westerlies or Indian monsoon is the sole dominant atmospheric process. The observed and simulated altitude-δ18O relationships strongly depend on the season and the domain (Indian monsoon or westerlies). Our results have crucial implications for the interpretation of paleoclimate records and for the application of atmospheric simulations to quantifying paleoclimate and paleo-elevation changes. © 2013. American Geophysical Union. All Rights Reserved.
Carrer D.,French National Center for Scientific Research |
Roujean J.-L.,French National Center for Scientific Research |
Hautecoeur O.,French National Center for Scientific Research |
Journal of Geophysical Research: Atmospheres | Year: 2010
This paper presents an innovative method for obtaining a daily estimate of a quality-controlled aerosol optical thickness (AOT) of a vertical column of the atmosphere over the continents. Because properties of land surface are more stationary than the atmosphere, the temporal dimension is exploited for simultaneous retrieval of the surface and aerosol bidirectional reflectance distribution function (BRDF) coming from a kernel-driven reflectance model. Off-zenith geometry of illumination enhances the forward scattering peak of the aerosol, which improves the retrieval of AOT from the aerosol BRDF. The solution is obtained through an unconstrained linear inversion procedure and perpetuated in time using a Kalman filter. On the basis of numerical experiments using the 6S atmospheric code, the validity of the BRDF model is demonstrated. The application is carried out with data from the Spinning Enhanced Visible and Infra Red Imager (SEVIRI) instrument on board the geostationary Meteosat Second Generation (MSG) satellite from June 2005 to August 2007 for midlatitude regions and from March 2006 to June 2006 over desert sites. The satellite-derived SEVIRI AOT compares favorably with Aerosol Robotic Network (AERONET) measurements for a number of contrasted stations and also similar Moderate Resolution Imaging Spectroradiometer (MODIS) products, within 20% of relative accuracy. The method appears competitive for tracking anthropogenic aerosol emissions in the troposphere and shows a potential for the challenging estimate of dust events over bright targets. Moreover, a high-frequency distribution of AOT provides hints as to the variability of pollutants according to town density and, potentially, motor vehicle traffic. The outcomes of the present study are expected to promote a monitoring of the global distributions of natural and anthropogenic sources and sinks of aerosol, which are receiving increased attention because of their climatic implications. Copyright 2010 by the American Geophysical Union.
Risi C.,University Pierre and Marie Curie |
Landais A.,LSCE |
Bony S.,University Pierre and Marie Curie |
Jouzel J.,LSCE |
And 2 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2010
Combined measurements of δ18O, δ17O, and δD in ice cores, leading to d excess and 17O excess, are expected to provide new constraints on the water cycle and past climates. We explore different processes, both in the source regions and during the poleward transport, that could explain the 17O excess increase by 20 per meg observed from the Last Glacial Maximum (LGM) to Early Holocene (EH) at the Vostok station. Using a singlecolumn model over tropical and subtropical oceans, we show that the relative humidity at the surface is the main factor controlling 17O excess in source regions. Then, using a Rayleigh-type model, we show that the 17O excess signal from the source region is preserved in the polar snowfall, contrary to d excess. Evaporative recharge over mid and high latitudes and δ18O seasonality in polar regions can also affect the Vostok 17O excess but cannot account for most of the 20 per meg deglacial increase from LGM to EH. On the other hand, a decrease of the relative humidity at the surface (rhs) by 8 to 22% would explain the observed change in 17O excess. Such a change would not necessarily be incompatible with a nearly unchanged boundary layer relative humidity, if the surface thermodynamic disequilibrium decreased by 4°C. Such a change in rhs would affect source and polar temperatures reconstructions from δ18O and d excess measurements, strengthening the interest of 17O excess measurements to better constrain such changes. Copyright 2010 by the American Geophysical Union.
News Article | February 2, 2016
Because of spiking levels of human-induced greenhouse gas emissions, global warming will possibly unleash devastating and extreme flooding in the coming years. Scientists say it will be similar to the severe storms that targeted a coastal plain in England in 2014. In a new report, a team of experts explained that climate change had "amplified" the violent storms that flooded Somerset Levels during late 2013 and early 2014. Now, man-made greenhouse gas emissions have upped the chances of extreme flooding by 43 percent, scientists said, as increasingly warmer temperatures hold larger amounts of moisture that lead to heavier downpour. "What was once a 1 in 100-year event in a world without climate change is now a 1 in 70-year event," said Oxford University's Friederike Otto, co-author of the report. Their paper is the first research to look into the likely role of climate change in the winter flooding of Somerset Levels. During December 2013 and January 2014, heavy rainfall poured down the coastal plain and wetland area of central Somerset in South West England, affecting Somerset, Dorset, Devon, Cornwall and the Thames valley. The downpour led to extensive flooding, where more than 5,000 houses and establishments, as well as 17,000 acres of agricultural land, were submerged. Losses amounted to more than £450 million ($647 million). The truth is, no single extreme weather occurrence can be linked to climate change, but Otto says it is more possible to estimate how much more likely an event is shaped by global warming. Aside from the Somerset Levels, Otto also calculated the severe flooding that occurred in Cumbria by Storm Desmond in December. Otto found that it was made 40 percent more possible by climate change, and that the record rainfall in the UK over the whole of that month was 50 to 75 percent more likely because of global warming. "We can definitely say with climate change that the issue of flooding isn't going to go away," said Otto. "As a society we need to think hard about the question of our vulnerability and exposure to flooding." The study also applied contributions from citizen scientists all over the world who had all used spare processing time on their computers to calculate more than 130,000 simulations of what the weather would have been like with and without human interference in the climate. According to Dr. Pascal Yiou of the Laboratoire des Sciences du Climat e l'Environnement (LSCE), the increase in amount of rainfall had been due to a rise in moisture. "The more extreme the weather, the stronger the effect of climate change over the UK," said Yiou. Meanwhile, Beate Werner, one of the authors of the report, said the recent flooding in the UK are adding to evidence of worsening flood problems across Europe, which has occurred also because of draining, barricading and building on the flood plains around major rivers. The Somerset Levels study, which is featured in the journal Nature Climate Change, was conducted by experts from LSCE and the Center for Ecology and Hydrology.
News Article | June 11, 2016
An extreme shift in the weather brought on by manmade emissions likely caused the torrential rains that flooded Paris last month, a new study says. Researchers at the Laboratory for Climate and Environment Sciences (LSCE) in France said the likelihood of unusual heavy rainfall, such as the one that caused the flooding of areas along the Seine River in May, has doubled in the past five decades as a result of global warming. They found that the probability of such extreme weather patterns happening had increased by more than 40 percent at the very least. LSCE senior scientist Robert Vautard said the rainstorms that flooded the French capital recently can be tied directly to the impacts of global warming on the Earth. During the three days of heavy raining, the water in the river Seine reached 6.07 meters (19.9 feet), which is the highest point it has ever been in the past three decades. The overflow from river tributaries forced thousands of people living in nearby towns to be evacuated. Torrential rains also caused widespread flooding in southern Germany, which destroyed several houses and vehicles. Reports say at least 18 people were killed in subsequent flooding in four European countries. The researchers, however, were not able to retrieve evidence from the heavy rainfall in Germany that it is strong enough to establish its potential connection to global warming. Despite this, the researchers believe that climate change may have also played a crucial role in the torrential rains in Germany. This only means that their observations were not in line with the climate models used, which would have allowed the researchers to draw robust conclusions similar to those from France. Climate scientists have found it difficult to establish a connection between extreme weather patterns, such as droughts and superstorms, and the impacts of climate change, which can take hundreds of years to measure. Richard Black, head of the London-based advocacy group Energy and Climate Intelligence Unit, explained that researchers are now able to make similar judgments such as provided by the LSCE study. He said that we now know that the heatwave in Europe and the heavy rainfall in the United Kingdom, which both occurred just last year, were made more likely because of climate change. Both events can be attributed to basic physics. As the atmosphere continues to become warmer, the more it is going to be able hold and discharge rainwater. Recent measurements show that the average surface temperature of the Earth has increased by as much as 1 degree Celsius (1.8 degrees Fahrenheit) as a result of manmade warming. If current trends continue, the temperature of the planet could rise up to 2 degrees Celsius (3.6 degrees Fahrenheit). This assessment takes into account efforts by national governments to reduce carbon emissions around the world. Satellite readings conducted for the past 25 years show that water vapor levels in the Earth's atmosphere have also increased by as much as 4 percent. This means that western and central Europe could continue to experience record-breaking rainfall events in the coming years. The findings of the Laboratory for Climate and Environment Sciences are set to be featured in the journal Hydrology and Earth System Sciences. © 2016 Tech Times, All rights reserved. Do not reproduce without permission.
Berg A.,LOCEAN |
Sultan B.,LOCEAN |
De Noblet-Ducoudre N.,LSCE
Geophysical Research Letters | Year: 2010
A large-scale crop model is forced by a range of climate datasets over West Africa to test the sensitivity of simulated yields to errors in input rainfall. The model skill, defined as the correlation between observed and simulated yield anomalies over 1968-1990 at the country scale, is used for assessment. We show that there are two essential rainfall features for the model to skillfully simulate interannual yield variability at the country scale: cumulative annual variability and frequency. At such a scale, providing additional information on intraseasonal variability, such as the chronology of rain events, does not improve the model skill. We suggest that such information is relevant at smaller spatial scales but is not spatially consistent enough to impact large-scale yield variability. Copyright © 2010 by the American Geophysical Union.