'Whole world' at risk from simultaneous droughts, famines, epidemics

Nafeez Ahmed in the "Earth Insight" blog at the Guardian (UK): An international scientific research project known as the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP), run by 30 teams from 12 countries, has attempted to understand the severity and scale of global impacts of climate change. The project compares model projections on water scarcity, crop yields, disease, floods among other issues to see how they could interact.

The series of papers published by the Proceedings for the National Academy of Sciences (PNAS) shows that policymakers might be underestimating the social and economic consequences of climate change due to insufficient attention on how different climate risks are interconnected.

One paper whose lead author is Franziska Piontek of the Potsdam Institute for Climate Impact Research explores impacts related to "water, agriculture, ecosystems, and malaria at different levels of global warming." The study concludes that: "... uncertainty arising from the impact models is considerable, and larger than that from the climate models. In a low probability-high impact worst-case assessment, almost the whole inhabited world is at risk for multisectoral pressures."

The uncertainties in the model are large enough that they may "mask" the risk of a "worst case" scenario of "multisectoral hotspots," where impacts affecting "water, agriculture, ecosystems, and health" overlap in ways that could affect "all the world's inhabited areas."

In the worst-case analysis, "Almost the entire global population is exposed to multisectoral pressure" at global mean temperatures of around 4C higher, with "roughly 18% of the global population" projected to "experience severe pressure in all four sectors. The affected regions are in Europe, North America, and south-east Asia."

How likely is this scenario? The study points out that: "This worst case is rather extreme, but nonetheless it represents the upper end of the risk spectrum in light of the large uncertainties."...

Detail on a church in Bretagne -- Christ descending into hell. Shot by Ifernyen, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license