Research funded by the U.S. National Science Foundation suggests if temperatures rise more than 3 to 5 degrees Fahrenheit above modern averages, parts of Peru and Bolivia will become a desert-like setting, an NSF release says.
Scientists say the change would be disastrous for the water supply and agricultural capacity of the 2 million inhabitants of La Paz, Bolivia's capital city.
Florida Institute of Technology climatologist Mark Bush led a research team investigating a 370,000-year record of climate and vegetation change in Andean ecosystems using fossilized pollen trapped in the sediments of Lake Titicaca, which sits on the border of Peru and Bolivia. They found that during two of the last three warming periods, between 130,000-115,000 years ago and 330,000-320,000 years ago, Lake Titicaca shrank by as much as 85 percent.
Adjacent shrubby grasslands were replaced by desert, and the steady warming caused trees to migrate upslope, just as they are doing today, researchers said.
As the climate kept warming, the system suddenly flipped from woodland to desert.
"The evidence is clear that there was a sudden change to a much drier state," said Bush.
Given the current rate of global warming, scientists say a tipping point could be reached between 2040 and 2050.
"The implications would be profound for some 2 million people," Paul Filmer, program director in NSF's Division of Earth Sciences, says.
Severe drought, and a loss of stored water in lakes in the region, would reduce yields from important agricultural regions and threaten drinking water supplies, he says.