Oct. 8, 2013 — Both freshwater availability for many millions of people and the stability of ecosystems such as the Siberian tundra or Indian grasslands are put at risk by climate change. Even if global warming is limited to two degrees above pre-industrial levels, 500 million people could be subject to increased water scarcity — while this number would grow by a further 50 percent if greenhouse-gas emissions are not cut soon. At five degrees global warming almost all ice-free land might be affected by ecosystem change.
“We managed to quantify a number of crucial impacts of climate change on the global land area,” says Dieter Gerten, lead-author of one of the studies. Mean global warming of 2 degrees, the target set by the international community, is projected to expose an additional 8 percent of humankind to new or increased water scarcity. 3.5 degrees — likely to occur if national emissions reductions remain at currently pledged levels — would affect 11 percent of the world population. 5 degrees could raise this even further to 13 percent.
“If population growth continues, by the end of our century under a business-as-usual scenario these figures would equate to well over one billion lives touched,” Gerten points out. “And this is on top of the more than one billion people already living in water-scarce regions today.” Parts of Asia and North Africa, the Mediterranean and the Middle East are particularly vulnerable.
Even greater changes ahead for the green cover of our planet
For the green cover of our planet, even greater changes are in store. “The area at risk of ecosystem transformation is expected to double between global warming of about 3 and 4 degrees,” says Lila Warszawski, lead author of another study that systematically compared different impact models — and the associated uncertainties — in order to gain a fuller picture of the possible consequences of climate change for natural ecosystems. This is part of the international Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP).