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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.

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.

News Article | June 11, 2016
Site: www.techtimes.com

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.

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 | Elias T.,LSCE
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.

McCulloch M.,University of Western Australia | McCulloch M.,CNR Marine Science Institute | Taviani M.,CNR Marine Science Institute | Montagna P.,LSCE | And 5 more authors.
Earth and Planetary Science Letters | Year: 2010

Uranium-series and radiocarbon ages are reported for deep-sea corals Madrepora oculata, Desmophyllum dianthus, Lophelia pertusa and Caryophyllia smithii from the Mediterranean Sea. U-series dating indicates that deep-sea corals have persisted in the Mediterranean for over 480,000years, especially during cool interstadial periods. The most prolific period of growth however appears to have occurred within the Younger Dryas (YD) period from 12,900 to 11,700years BP followed by a short (~330years) phase of post-YD coral growth from 11,230 to 10,900years BP. This indicates that deep-sea corals were prolific in the Mediterranean not only during the return to the more glacial-like conditions of the YD, but also following the rapid deglaciation and transition to warmer conditions that followed the end of the YD. Surprisingly, there is a paucity Last Glacial Maximum (LGM) coral ages, implying they were largely absent during this period when cold-water conditions were more prevalent. Radiocarbon ages show that the intermediate depth waters of the Mediterranean generally had {increment}14C compositions similar to surface waters, indicating that these waters were extremely well ventilated. The only exception is a narrow period in the YD (12,500±100years BP) when several samples of Lophelia pertusa from the Ionian Sea had {increment}14C values falling significantly below the marine curve. Using a refined approach, isolation ages (τisol) of 300years to 500years are estimated for these intermediate (800-1000m) depth waters relative to surface marine waters, indicating a reduction or absence of deep-water formation in the Ionian and adjacent Adriatic Seas during the YD. Contrary to previous findings, we find no evidence for widespread intrusion of low {increment}14C Atlantic waters into the Mediterranean. Prolific growth of deep-sea corals in the Mediterranean ended abruptly at ~10,900years BP, with many of the coral-bearing mounds on the continental slopes being draped in a thin veneer of mud. Their demise is attributed to a number of factors, including the direct loss of habitat due to high sedimentation that accompanied glacial meltwater pulses, together with rising temperatures that would have finally pervaded the deeper water of the Mediterranean following the onset of Holocene warming. © 2010 Elsevier B.V.

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