New research disproves supposed tropical 'thermostat'

March 6 (UPI) -- New research suggests the tropics will continue to warm along with the rest of the planet, contrary to the predictions of scientists who believe the tropics possess an internal "thermostat."

Previous studies have suggested the tropics boast a thermostat of sorts -- climate patterns that keep the region's temperatures from rising above a certain threshold, even as the rest of the globe warms dramatically.

But new research suggests no such thermostat exists, and that temperatures in the tropics surpassed deadly levels some 56 million years ago.

New paleoclimate data and the latest modeling suggest the tropics warmed 3 degrees Celsius Paleocene-Eocene Thermal Maximum, a period that saw the rest of Earth warm 5 degrees -- the warmest Earth's been in the last 100 million years.

"The records produced in this study indicate that when the tropics warmed that last little bit, a threshold was passed and parts of the tropical biosphere seems to have died," Matthew Huber, a professor of planetary sciences at Purdue University, said in a news release. "This is the first time that we've found really good information, in a very detailed way, where we saw major changes in the tropics directly associated with warming past a key threshold in the past 60 million years."

The new findings -- detailed in the journal Science Advances -- were made possible by the discovery of shells in ancient marine sedimentary deposits excavated in Nigeria.

"We don't find 50-million-year-old thermometers at the bottom of the ocean," Huber said. "What we do find are shells, and we use the isotopes of carbon and oxygen within the shells, complemented by temperature proxies from organic material, to say something about the carbon cycle and about the temperature in the past."

Understanding how global warming will affect the tropics is an important part of climate science. The majority of Earth's human population and biodiversity live in the subtropics and tropics.

"If you say there's no tropical thermostat, then half of the world's biodiversity -- over half of the world's population, the tropical rainforests, the reefs, India, Brazil -- these populous and very important countries have nothing to prevent them from warming up substantially above conditions that humans have been used to," Huber said.