Study: Tropical Rainforests Benefited from Past Rapid Warming

Published November 29, 2010

Tropical rainforests experienced sensational growth and an explosive increase in biodiversity during a period of rapid global warming 56 million years ago, scientists report in the journal Science.

The findings refute forecasts of imminent global warming-induced tropical rainforest demise published by the United Nations Intergovernmental Panel on Climate Change (IPCC) and provide strong evidence many of the benefits of warming temperatures that occurred during the 20th century are likely to continue for the foreseeable future.

History Contradicts Computer Models
IPCC forecasts of tropical rainforest demise are predicated on computer programs predicting drier tropical conditions as temperatures rise. Researchers at the Smithsonian Tropical Research Institute (STRI), however, found that during the Paleocene-Eocene Thermal Maximum (PETM)—a period of much warmer temperatures than today, when global temperatures rose by 6 degrees Celsius (11 degrees Fahrenheit) within a few thousand years—precipitation remained abundant, plant life flourished, and new plant species evolved and proliferated much faster than other plant species died out.

STRI staff scientist Carlos Jaramillo and colleagues published the report on global warming effects on tropical rain forests in Science on Nov 11.

“Our research did not find any evidence of dryness in the northern neotropics during the warming of the PETM,” lead author Jaramillo told Environment & Climate News.

During the PETM period, temperatures across the world were 3 to 5 degrees Celsius warmer and atmospheric carbon dioxide levels 2.5 times higher than today. With the rapid increase in temperature and carbon dioxide levels during the PETM, the study suggests forests thrived in the warmer, wetter periods.

Passionflower, Chocolate Took Root
Researchers examined pollen trapped in rock cores and outcrops from Columbia and Venezuela from before, during, and after the PETM. Plant life was found to have increased rapidly during the warming event, and plant species such as the passionflower plant family and the chocolate family appeared for the first time.

Warmer, wetter weather may boost plant life, but Jaramillo warned about present-day deforestation in which Third World farmers and other developers destroy forests to turn them over to other uses.

“Back in the PETM, deforestation was not a problem, but today it is. And how deforestation affects local microclimate is a subject of intense research,” he said.

Alyssa Carducci ([email protected]) writes from Tampa, Florida.