Caroline de Malet
Le Figaro, 15/05/2008 a close correlation between the concentration of greenhouse gases and temperatures recorded in Antarctica. Accrediting the idea that the warming is attributable to human activities.
For twenty years, scientists have continued to test this hypothesis over periods of longer and longer. By drilling deeper and deeper, in the framework of the European Epica: one thousand, two thousand, more than three thousand meters. Today, two international teams of researchers, mostly French, published in the journal Nature the latest results of this analysis for 800 000 years, dealing respectively with CO2 and methane. Paleoclimatologists had never risen as far back in time. If the analysis of carbon dioxide is always based on samples from two Antarctic sites (the Russian base of Vostok ice for from today to 420 000 years and the Franco-Italian site drilling Dome C cores dating from 650 000-800 000 years), the methane was performed on the same core conclusion from Dome C, with a measurement point every meter (or every 380 years).
The result of this titanic work conducted over the past 20 years confirms many hypotheses, but also brings its share of surprises. Among the confirmations, scientific have identified nine climatic cycles of alternating glacial and interglacial (warmer). One more a few years ago, where they were identified only eight. Another major conclusion: never, during this long period of several hundreds of thousands of years, was found a CO2 concentration as high as today. "With 800 000 years of archives, the chances of missing a peak comparable to the one we know today are becoming more minimal," said Jerome Chappelaz, deputy director of the Laboratory of Geology and glaciology Environment (LGGE) in Grenoble and co-author of the work on the methane.
The most striking episode warm identified the period dates back to 320 000 years. The CO2 content was then 320 parts per million (ppm) against over 380 now and the methane concentration of 780 ppm (cons 1800 today). It was then 3-5 degrees higher than today's South Pole. But, says Jerome Chappelaz, "unlike the recent period, which this evolution occurred in 150 years, during this last episode, it took place over several thousand years, which has been given time to to stabilize climate. " Rapid change
Among the harvest of lessons delivered by these works, "we found the lowest levels ever recorded in CO2 667 000 years ago," says Dominique Raynaud, a former director of LGGE and coauthor of study devoted to CO2.
The atmosphere was experiencing carbon dioxide concentration of 172 ppm, more cons than 380 ppm today. "One that may be explained by the role of CO 2 capture by the oceans, which has been more effective at certain times today," said Dominique Raynaud. The study on
Methane shows it, with time increasing the intensity of monsoons in Southeast Asia is consistent with the increase of the methane content in the atmosphere. A new observation is explained in part by the role played by moisture, snow cover of the Tibetan plateau and sunshine. Last
contribution of this work: the rapid climate changes observed in each of the glaciations can not be explained either by the duration of glaciations either by their intensity. Researchers have even noticed when glaciation occurred 770 000 years ago. In fact, these episodes are systematic. "It is surprising because it was expected that they depend on the volume of ice caps in the North Atlantic, but this is not the case, do not hide Jerome Chappelaz. What
question the idea, widespread, that the thermohaline circulation may slow during hot, which could result in a cooling of Europe. Nothing like this has been observed in the past. A real stir, which will not fail to stir.
0 comments:
Post a Comment