Tropical Ecosystems Boost Carbon Dioxide as Temperatures Increase: A Study

Unlike in other parts of the word, tropical ecosystems are capable of generating significant carbon dioxide when temperatures rise, an international team of researchers has found.

Specifically, the scientists discovered that a temperature increase of just 1 degree Celsius in near-surface air temperatures in the tropics results in an average annual growth rate of atmospheric carbon dioxide that is equivalent to one-third of the annual global emissions caused by the combustion of fossil fuels and deforestation combined.

Knowing this, they report, can only help in improving understanding of the global carbon cycle.

"What we learned is that in spite of droughts, floods, volcano eruptions, El Niño and other events, the Earth system has been remarkably consistent in regulating the year-to-year variations in atmospheric carbon dioxide levels," Weile Wang, a research scientist at NASA's Ames Research Center and lead author of a paper published, said in a press release.

Published in the Proceedings of the National Academy of Sciences, the study provides further support for the "carbon-climate feedback" hypothesis proposed by many scientists, which asserts a warming climate will lead to accelerated carbon dioxide growth in the atmosphere from vegetation and soils.

Other Earth system processes, such as droughts and floods, contribute to changes in the atmospheric carbon dioxide growth rate; however, the new finding demonstrates that observed temperature changes are a more important factor than rainfall changes in the tropics, according to those behind it.

During the course of their research the team used a state-of-the-art, high-performance computing and data access facility called NASA Earth Exchange (NEX) at Ames in order to come to a better understanding of the mechanisms underlying the relationship between carbon dioxide levels and increased temperatures. For example, using the center they were able to analyze widely available data of atmospheric carbon dioxide concentrations and global air temperatures between 1959 and 2011, while studying outputs from several global dynamic vegetation models.

"Climate warming is what we know with certainty will happen under climate change in the tropics," said Josep G. Canadell, executive director of the Global Carbon Project in Canberra, Australia, and co-author on the paper.

What this then implies is that the release of carbon dioxide from the tropical ecosystems will likely be accelerated with future warming, the scientists conclude.

Events that can temporarily influence climate, such as volcanic eruptions, may disturb the strength of the relationship between annual temperature and carbon dioxide growth for a few years, but the coupling always recovers in the end, according to the researchers.

"The study really highlights the importance of long-term Earth observations for improving our understanding of the Earth system," said Rama Nemani, principal scientist at Ames for the NEX project. "Conclusions drawn from analysis of shorter records could be misleading."

The study was supported by the Earth Science Division in the Science Mission Directorate at NASA Headquarters in Washington.