MELBOURNE, FLA.—Catastrophic drought is imminent for the capital city of Bolivia, according to new research into the historical ecology of the Andes. If temperatures rise more than 1.5 to 2oC (3 to 5oF), the Altiplano of Peru and Bolivia will become desert-like. This change would be disastrous for the water supply and agricultural capacity of the two million inhabitants of La Paz. The data, derived from research at Florida Institute of Technology, recently appeared in Global Change Biology.
Florida Tech 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, Peru/Bolivia. His team found that during two of the last three interglacial periods, which occurred between 130,000 and 115,000 years ago and 330,000 and 320,000 years ago, Lake Titicaca shrank by as much as 85 percent and adjacent shrubby grasslands were replaced by desert conditions.
In each case a steady warming occurred that caused trees to migrate upslope, just as they are doing today. However, as the climate kept on warming the area went from wooded to desert-like. Bush said, “The evidence is clear that there was a sudden change to a much drier state.”
Evidence for the flip is also documented in work by his collaborators. Diatomologist, Sherilyn Fritz of University of Nebraska-Lincoln, showed that during these warm episodes the algae living in the lake shifted from freshwater species to those tolerant of salty water. Also, Paul Baker of Duke University, identified peaks of carbonate deposition. Both strands of evidence point to a sudden shallowing of the lake due to evaporative loss.
The environmental reconstruction shows that with moderate warming, forests moved upslope. As that warming continued, however, a climatic tipping point was exceeded, which threw the system into a new, drier state that halted forest expansion. The tipping point is caused by increasing the evaporative loss from Lake Titicaca. As the lake contracts, the local climatic effects attributable to a large lake—a local doubling of rainfall, being the most important—would be lost. Such tipping points have been postulated by other studies, but this study allowed the researchers to define when the system will change.
Based on the growth limits of Andean forests, the researchers ascertained that the tipping point was exceeded within a 1.5 to 2 oC warming above modern conditions. Given an observed rate of warming in the Peruvian Andes of about 0.3 to 0.5 oC per decade, the tipping point would be reached by about A.D. 2040-2050.
The implications of warming would be profound for the two million inhabitants of the Altiplano. Severe drought and a loss of stored water in lakes would reduce yields from the important agricultural region and threaten drinking water supplies. The research suggests that limiting wildfires would help to delay the worst effects of the drought.
To see the full article, visit: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2010.02203.x/abstract.