For the first time, they have reconstituted tthe evolution, over 800,000 years, of levels of carbon dioxide and methane, the two main greenhouse gases after water vapor. With these new numbers, the researchers now have access to data which will help them better predict future climate changes on earth. The results are published in two articles in the 15 May 2008 issue of /Nature/.*
In the absence of greenhouse gases (water vapor, carbon dioxide, methane...), the average temperature on earth would be -18°C, resulting in conditions unable to sustain life. The concentration of these gases in the atmosphere has substantially increased over time, due to human activity (fossil fuel combustion, development of agriculture). Studying the evolution of these concentrations allows us to better understand their interaction with the earth's climate, and this type of study is carried thanks to ice cores, which contain the only available records of greenhouse gas levels.
An ice core drilled in Antartica near the Franco-Italian base Dome Concordia, as part of the EPICA project, reached 3270 meters in December 2004, stopping a few meters above solid rock. At these depths, the ice dates back 800,000 years, or 8 glaciary-interglaciary climatic cyles. This is the oldest ice ever cored until now, and the analysis of gas bubbles trapped in the ice has allowed recordings of levels of carbon dioxide (CO2) and methane (CH4) in the atmosphere 800,000 years ago (previous recordings only went back as far as 650,000 years ago). In light of these new measurements, researchers have access, for the first time, to reference curves for levels of CO2 and CH4, showing the evolution of the gases in ancient times. This is precious information for scientists attempting to understand the correlation between climate change on earth and the carbon cycle. These results give hope for better predictions of future levels of greenhouse gases, and in theory, of the earth's climate.
This work has already enabled researchers to make major progress in certain areas. It confirms the close correlation between temperatures recorded in Antartica in the past and atmospheric levels of CO2 and CH4. Another significant observation is that never, in 800,000 years, have greenhouse gas levels been as high as they are today (current levels surpass 380 ppmv (5) for CO2 and 1800 ppbv (6) for CH4). The CO2 curve also shows that the lowest levels ever recorded were 172 ppmv, 667,000 years ago. Moreover, researchers have shown the existence of a modulation in atmospheric CO2 levels on a relatively long time scale, namely several hundreds of thousands of years. This unique phenomenon could stem from the more of less significant intensity of continental erosion which affects the carbon cycle over large time scales.Thanks to the remarkably detailed records of atmospheric methane, researchers have noted an increase over time in the periodicity of a component called precession . This signal, which is correlated to monsoon intensities in South East Asia over millenia, probably reflects an intensification of the monsoon in tropical regions over the last
which helps to redistribute temperature around the globe). The issue of why this phenomemon appears at the beginning of the ice ages remains to be explained.
(6) This means that for every billion air molecules, 1800 are CH4 molecules. ppbv = part per billion in volume.*BIBLIOGRAPHY*
Orbital and millennial-scale features of atmospheric CH4 over the last 800,000 years. Loulergue, L., A. Schilt, R. Spahni, V. Masson-Delmotte,T. Blunier, B. Lemieux, J.-M. Barnola, D. Raynaud, T.F. Stocker, and J. Chappellaz. /Nature/. 15 May 2008.
Julien Guillaume | alfa
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China's Loess Plateau was formed by wind alternately depositing dust or removing dust over the last 2.6 million years, according to a new report from University of Arizona geoscientists. The study is the first to explain how the steep-fronted plateau formed.
China's Loess Plateau was formed by wind alternately depositing dust or removing dust over the last 2.6 million years, according to a new report from...
The leaves of the lotus flower, and other natural surfaces that repel water and dirt, have been the model for many types of engineered liquid-repelling surfaces. As slippery as these surfaces are, however, tiny water droplets still stick to them. Now, Penn State researchers have developed nano/micro-textured, highly slippery surfaces able to outperform these naturally inspired coatings, particularly when the water is a vapor or tiny droplets.
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Longer, more severe, and hotter droughts and a myriad of other threats, including diseases and more extensive and severe wildfires, are threatening to transform some of the world's temperate forests, a new study published in Science has found. Without informed management, some forests could convert to shrublands or grasslands within the coming decades.
"While we have been trying to manage for resilience of 20th century conditions, we realize now that we must prepare for transformations and attempt to ease...
A University of Oklahoma astrophysicist and his Chinese collaborator have found two supermassive black holes in Markarian 231, the nearest quasar to Earth, using observations from NASA's Hubble Space Telescope.
The discovery of two supermassive black holes--one larger one and a second, smaller one--are evidence of a binary black hole and suggests that supermassive...
A team of European researchers have developed a model to simulate the impact of tsunamis generated by earthquakes and applied it to the Eastern Mediterranean. The results show how tsunami waves could hit and inundate coastal areas in southern Italy and Greece. The study is published today (27 August) in Ocean Science, an open access journal of the European Geosciences Union (EGU).
Though not as frequent as in the Pacific and Indian oceans, tsunamis also occur in the Mediterranean, mainly due to earthquakes generated when the African...
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