According to a slew of new studies, released by the German Potsdam Institute for Climate Impact Research (PIK), the world will face drastic changes to water availability and growth of vegetation over the next century, even if radical mitigation action is taken now.  

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The publication of the new Potsdam research coincides with the release of the UN-convened IPCC's landmark report, which provided 'unequivocal' evidence to suggest human activity is driving climate change around the world. 

"We managed to quantify a number of crucial impacts of climate change on the global land area," said Dieter Gerten, lead-author of one of the PIK studies. According to Dr Gerten, mean global warming of 2 degrees, the target set by the international community, is projected to expose an additional 8 percent of humankind (around 560 million people) 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. A 5 degree rise would be devastating and affect yet more people.

Dr Gerten elaborated, "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. 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 to water scarcity.

Climate changes to affect planet's 'green cover'

In a separate but complementary study, climate scientist Lila Warszawski found that the Earth's 'green cover' is set to suffer as a result of water scarcity and global warming. "The area at risk of ecosystem transformation is expected to double between global warming of about 3 and 4 degrees," she said.  Warszawski systematically compared different models in order to gain a fuller picture of the possible consequences of climate change for natural ecosystems.

Her findings are sobering; a warming of 5 degrees, likely to happen in the next century if climate change goes on unabated, would put nearly all terrestrial natural ecosystems at risk of severe change. "So despite the uncertainties, the findings clearly demonstrate that there is a large difference in the risk of global ecosystem change under a scenario of no climate change mitigation compared to one of ambitious mitigation," commented fellow Potsdam researcher Sebastian Ostberg.

Another influential PIK scientist, Wolfgang Lucht, added an even starker warning; "Our findings support the assertion that we are fundamentally destabilizing our natural systems – we are leaving the world as we know it."

The regions at risk under unabated global warming include the grasslands of Eastern India, shrublands of the Tibetan Plateau, the forests of Northern Canada, the savannas of Ethiopia and Somalia, and the Amazonian rainforest. Many of these are regions of rich and unique biodiversity.

Studies by Warszawski and Sebastian Ostberg used modelling to examine where changes would occur, either to the spread of vegetation or storage of carbon and water. The 'biosphere simulation models' were used to compare hundreds of climate change scenarios and highlight which regions would be most likely to face critical impacts of climate change first.

Hans Joachim Schellnhuber, the institute's director, said, "The increase in water scarcity that we found will impact on the livelihoods of a huge number of people, with the global poor being the most vulnerable."

Echoing the findings of the IPCC scientists, Schellnhuber said that, even though some changes are inevitable, there is an urgent need for drastic action on climate change. Advising that policy makers must take responsibility and step up mitigation efforts, he implored, "This might get buffered to some extent through adaptation measures such as expanding of irrigated cropland. However, such an expansion would further increase the pressure on Earth's ecosystems and water resources. Now this is not a question of ducks and daisies, but of our unique natural heritage, the very basis of life. Therefore, greenhouse-gas emissions have to be reduced substantially, and soon."

Experts including Lord Stern, author of a groundbreaking government report on the economic impacts of climate change, warned in late September that the IPCC scientists would understate the risks posed in their report, and provide conservative estimates based on areas where current climate knowledge is strongest. Even so, he said then that for anyone to underestimate the threat posed by climate change would be "absurd".