Global warming will reduce glaciers and snowpack around the world, causing water shortages and other problems that will impact millions of people, US scientists warned on Wednesday.
Human-produced greenhouse gases, and the resulting warmer climates, will have a significant influence on ice- and snow-dependent regions and result in costly disruptions to water supply and resource management systems, said researchers at the Scripps Institution of Oceanography.
In a paper published in the Nov. 17 issue of the journal Nature, the researchers said their predictions and observations "portend important issues for the water resources of a substantial fraction of the world's population."
More water will fall in the form of rain rather than snow in a warming climate, filling reservoirs to capacity earlier than normal. Additionally, a warming climate will result in snow melting earlier in the year than in the previous decades, disrupting the traditional timing of water available from snow runoff streams, the researchers analyzed.
Together, these changes mean less snow accumulation in the winter and earlier snow-derived water runoff in the spring, challenging the capacities of existing water reservoirs.
According to Tim Barnett, the lead author of the paper, water shortages will occur in areas where reservoir capacity cannot hold the annual cycle of rain or snow, such as California in the United States.
For Canada, earlier spring water runoff will threaten agricultural production. In Europe, climate warming in the Rhine River Basin may reduce peak-demand water availability for industrial applications, agriculture and household uses.
Ship transportation, flood protection, hydropower generation and revenue from skiing all could be threatened as a result, Barnett said.
The researchers warned that regions depending on glaciers for water supply will be most vulnerable in the coming decades, "because once the glaciers have melted in a warmer world, there will be no replacement for the water they now provide."
These regions include China, India and other parts of Asia. The ice mass in the mountainous area of this region is the third largest on Earth following Arctic-Greenland and Antarctica, the researchers said.
Similarly, a significant fraction of the population west of the Andes Mountains in South America could be at risk due to shrinking supplies of glacier-derived river water.
Glacier-covered areas in Peru have experienced a 25-percent reduction in the past three decades, and some glaciers may disappear in a few decades or sooner, according to the paper.
"Climate warming is a certainty in our future and the bottom line in this analysis is that we looked at the impact of the warming and the long-term prognosis is clear and very dire," Barnett said.
"It's especially clear that regions in Asia and South America are headed for a water supply crisis because once that fossil water (glacier) is gone, it's gone."
Adding to the complexity of these scenarios is determining the role of tiny atmospheric particles called aerosols.
Such particles are believed to cool the planet's surface and alter cloud processes. But while common aerosols such as black carbon are found in many regions around the world, their influence is not likely to reverse or even neutralize greenhouse warming, the paper said.