What’s especially significant is that most of the damage gets done by relatively low amounts of global warming. The researchers at the Potsdam Institute for Climate Impact Research in Germany, who carried out the modeling, chose as their central framework the RCP8.5 — a future scenario of global warming laid out by the Intergovernmental Panel on Climate Change (IPCC), which assumes a business-as-usual path for carbon emissions. The projections of future population growth relied on the middle-of-road SSP2 scenario. When the researchers looked for the greatest overlap between the results, they found that 1°C to 2°C of global warming drove up absolute water scarcity around the world by 40 percent. That was due to climate change alone, before the effect of population growth was factored in. At 3°C of warming, climate change’s effect falls to just 25 percent of the increase in scarcity, as population growth takes over. But the severe impacts continued well past 2°C of warming.
“Absolute water scarcity” is defined as access to less than 500 cubic meters of water per person per year. “Chronic water scarcity” is access to 1,000 cubic meters or less every year. The global average for water consumption per person is 1,200 cubic meters per year, and the number gets considerably higher in advanced western countries.
The study involved taking eleven different computer models of water flow and use around the globe, and then running them through five global climate scenarios — a simulation “of unprecedented size” according to the Institute’s press release.
As far as the changes for absolute levels of water scarcity, the researchers determined that 1.5 percent of the global population currently struggles with absolute water scarcity, and 3 percent faces chronic water scarcity. At 1°C of warming that rises to 6 percent and 13 percent, respectively; at 2°C it hits 9 percent and 21 percent; and at 3°C it reaches 12 percent and 24 percent of all people around the world.
So add this finding to the growing body of evidence that even the 2°C threshold may come with far more upheaval than the world’s governments currently anticipate.
The areas that were hardest-hit under the modeling were the Mediterranean, the Middle East, the southern United States, and southern China. As climate change involves a lot of regional variability, southern India, western China, and parts of eastern Africa actually saw water availability go up. It’s just that, as the headline numbers show, the total change is a big net negative.
Without drastic corrective action, and soon, the world is actually on track to blow past the 2°C (3.6°F) of global warming scientists view as the threshold beyond which climate change becomes truly catastrophic. Water shortages are a big part of that destructive effect. Shortages are already projected for major American river basins, they threaten major urban populations around the world. Water scarcity bodes ill for humanity’s future energy prospects, given the centrality of water in most fossil fuel power generation.
Water scarcity is also one of the chief ways climate change could destabilize international security. The flood of Syrian refugees into Jordan is exacerbating Jordan’s already chronic water shortages, and thus inflaming tensions in the region.