Page 26

CIM32

w 26 | Focus cnrs I international magazine REUTERS /Krause R. ©That the Earth’s climate goes through changes is an undisputable fact, as witnessed by the long glacial periods that occurred in the past. Complex, dynamic, and in constant evolution, the climate is affected by a variety of factors including the Earth’s orbit around the Sun, solar activity, atmospheric movements, and the water cycle. The list is long, and the mindboggling number of parameters renders year scale, the climate’s inherent chaotic predictions particularly difficult. nature makes interpretation difficult. For Nonetheless, researchers are sure of one example, the most recent analyses show a thing: human activity is affecting our slowdown in the warming trend. “This climate’s delicate mechanism. type of observation does not cast doubt on the reality of global warming,” AN ELEMENT OF UNPREDI CTABILITY Dufresne insists. “But the more we try to The Earth’s atmosphere naturally contains so-called greenhouse keep a close watch, the more limited we gases, primarily water vapor and carbon dioxide, which prevent are in time and space for lack of the planet’s energy from escaping into space, and maintains a available observations, and the more livable temperature on its surface. Without these gases, the average the climate’s natural variability comes temperature on Earth would be –18°C instead of the 15°C to the fore.” As of today, there is no direct method to solve this problem. WAITING FOR AN SWER S Of course, the analyses of past climate change can give valuable information on we have today. As Jean-Louis Dufresne of the LMD1 points out, “when the water vapor and CO2 levels change, so does the greenhouse effect. As a result, our planet’s energy balance, therefore its climate, is altered. This is an undeniable scientific fact.” Indeed, the amount of atmospheric CO2 has risen sharply over the past century, coinciding with the emergence of a fossil-fueled industrial economy. As for water vapor concentrations, although they are essentially unaffected by human activity, they strongly depend on the climate, and affect it in return through a subtle interplay of actions and reactions. Although knowledge is constantly increasing in this field, researchers are still far from having a complete understanding of climate change and of its effects and severity in the future. And this is not only due to a lack of accuracy of the numerical models used to simulate past and future climates, or to the margin of error in interpreting evidence of past climates. “There is an element of unpredictability in the climate that science will never be able to quantify,” explains IPSL director Hervé Le Treut. Even without human disruptions, the climate inevitably fluctuates, at all scales and seemingly at random. “It is a chaotic system,” Dufresne says. “On the scale of a decade, the effect of anthropogenic and natural perturbations cannot be distinguished from the climate’s purely random evolutions.” Temperature change is a telling example. On the scale of a century, the increase is easily measurable (+0.9°C, plus or minus 0.2°C, since 1900). Human activity and the resulting intensification of the greenhouse effect are the most obvious cause for this rise. But on a 10 or 20 Climate Change: Facts and Uncertainties 15 The Maldives archipelago could disappear completely as sea levels rise. 15


CIM32
To see the actual publication please follow the link above