A Warming with Multiple Consequences
It is rather common, sometimes rightfully so, for our community to be criticized for being catastrophists when we broach aspects connected to the consequences of climate change. Alongside our knowledge of the climatic system and its evolution, that of the impacts that a warming would have has progressed greatly in the last twenty years. We now also rely largely on the 2007 IPCC Group II report, which is dedicated to the impacts of climate change and to our adaptation and vulnerability to it.1 Thanks to that synthesis, we will reveal the world toward which we risk evolving if nothing is done to limit greenhouse gas emissions. Before turning to the glaciers and polar regions, we will take a quick look at consequences on a global scale.
Intuitively we expect that the consequences of climate change will increase as the temperature rises; they will also depend on the evolution of climatic extremes that contribute in an important way to the damage. This is indeed the case, as is seen at point 1 in table 14.1, which presents a synthesis of the main consequences of climate warming according to large sector: water, ecosystems, food, coastal areas, and health (Table 14.1). Thus the threshold of 1.5 to 2.5°C appears critical for the maintenance of biodiversity—greater warming leads to important changes in the structure and functioning of ecosystems— and in the ability of continental ecosystems to play their role of carbon pumps. In the ranks of particularly vulnerable ecosystems are the tundra, the boreal forest, ecosystems of mountain regions sensitive to warming, and those in the Mediterranean or certain forests in tropical regions as a result of the decrease in precipitation.