Although uncertainties remain, the increase of CO2 is the main cause of warming.
The conclusions of the Academy of Sciences are clear, crisp and clear: "Since the second half of the nineteenthe century, several independent indicators clearly show a warming climate, modulated in time. "And the text says, this temperature increase was primarily due to the increased concentration of CO2 in the atmosphere itself due to "doubt" to human activity. "The fluctuations in solar activity over the last forty years can not be a dominant factor," he says finally.
In presenting these findings on Thursday morning to the Minister of Research, Valérie Pécresse, the Academy of Sciences will perhaps succeed in giving a halt to particularly contentious debates that took place between last spring, hundreds of researchers working climate in which few climatosceptiques Claude Allegre, former Minister of Education. The latter had just published a book, tellingly The climate Sham , In which he placed particular because the work of the IPCC (Intergovernmental Panel on Climate Change), denouncing global mobilization "around a myth without foundation." Six hundred scientists signed a petition to ask leading Valerie Pécresse it organizes the Academy for a "thorough debate" in order to "establish the present state of scientific knowledge on climate change."
"The right to evolve"
After written submissions and a day of debate involving more than two dozen foreign experts held in closed session on September 20, quai Conti, Paris, academics have adopted Wednesday night, the report led by Jean-Loup Puget, delegate of the science section of the universe, and Rene Blanchet, president of the group climate of the environment committee.
A report signed by Claude Allegre, which has been told to Jean Salençon, president of the Academy of Sciences, the former minister "has the right to evolve." "I always say the same thing," replied the person immediately. I never said that CO2 played no role, I say that the importance of CO2 is not proven. "
The document anyway does not stop at only evidence of warming. It also extends extensively on several other points and uncertainties that may accompany them. This is true of the need to use climate models to understand the system and "the tests to validate them." The Academy endorses the relevance of projections of climate change at thirty or fifty years. "These projections are particularly useful in responding to current societal concerns, exacerbated by the anticipated increase in population." But she also recalls that "the assessment of uncertainty is at the heart of debates".
If the results of all models that revolve around the world are relatively homogeneous on the impact of CO2 and effects of water vapor, "gaps are important on the role of clouds," said Jean-Loup Puget. "The evolution of the cloud is universally recognized as the most uncertain. Clouds exert two opposing effects: a parasol effect, returning the solar flux to space, and a greenhouse, "the report said. Significant uncertainties remain also on the growth of sea ice and polar ice caps, the ocean-atmosphere coupling, the evolution of the biosphere and the dynamics of the carbon cycle. " Claude Allegre, "this text is a compromise, but it is satisfying, because the uncertainty in the knowledge that one has explicitly included climate," says he. Vincent Courtillot, director of the Geophysical Institute of the globe and climate skeptics claimed, hopes that the report "will pacify the debate."
For their part, two of the leading French specialists in climate science, Jean Jouzel and Hervé LeTreut, said they were also quite satisfied with the outcome. "This is a document that clearly reaffirms the key findings of the IPCC," says first co-winner of the Nobel Peace Prize 2007 and Vice Chairman of the Panel. "The most important thing is that it shows that scientists who were attacked were working methods trustworthy," says his side LeTreut Herve, a member of the Academy and Specialist climate models. "There is no debate among scientists and society without trust. I hope this report will contribute, "he adds.
For her part, Valerie Pecresse, stressing "this unambiguous statement of the impact of human activities on the environment," said that "investment for the future are a major opportunity to strengthen research on climate change." And cite "numerous facilities projects of excellence associated with satellite observations" that will "sound the ice caps, the ocean floor, the study of clouds, modeling …."