May 31, 2013
Rainforests Thrived In Soaring Temperatures Millions Of Years Ago
April Flowers for redOrbit.com - Your Universe Online
Paleontologists at the Smithsonian Tropical Research Institute say that South American rainforests have thrived during three extreme global warming events in the past. Currently, no tropical forests in South America experience average yearly temperatures over 84 degrees Fahrenheit. By the end of the century, however, average global temperatures are predicted to rise by another 1 degree, leading some scientists to predict the death of the world´s most diverse terrestrial ecosystem.
In order to create a deep-time perspective for the debate, almost 6,000 published measurements of ancient temperatures were reviewed by Carlos Jaramillo, the Cofrin Chair in Palynology at the Smithsonian Tropical Research Institute, and AndrÃ©s CÃ¡rdenas, post-doctoral fellow at the Smithsonian in Panama.
"To take the temperature of the past we rely on indirect evidence like oxygen isotope ratios in the fossil shells of marine organisms or from bacteria biomarkers," said Jaramillo.
120 million years ago in the mid-Cretaceous period, intense volcanic activity produced huge quantities of carbon dioxide, raising yearly temperatures in the South American tropics by nearly 9 degrees Fahrenheit. Temperatures rose again by 5 degrees in a period of less than 10,000 years about 55 million years ago during the Paleocene-Eocene thermal maximum. Temperatures soared again around 53 million years ago.
The fossil record shows that rainforests prospered under these heated conditions, and diversity increased. Higher diversity during warming events could be explained by the expansion of tropical forests into temperate areas because larger areas of forest generally sustain higher diversity than smaller areas do.
"But to our surprise, rainforests never extended much beyond the modern tropical belt, so something other than temperature must have determined where they were growing," said Jaramillo.
Jaramillo and CÃ¡rdenas' report, published in the Annual Review of Earth and Planetary Science, refers to findings by Smithsonian plant physiologist Klaus Winter that leaves of some tropical trees tolerate short-term exposure to temperatures up to 122 F. Much less water is used by trees when carbon dioxide concentrations double, lending further evidence to the theory that tropical forests are resilient to climate change.