Friday, April 27, 2018 - 3:08pm

New research published in Nature Climate Change and led by assistant professor of geography Gabriel Kooperman identifies an unexpected but major factor in worldwide precipitation shifts: the direct response of tropical forests to higher levels of carbon dioxide:

“People tend to think that most of the disruption will come from heat going into the oceans, which, in turn, will alter wind patterns,” said James Randerson, UCI’s Ralph J. & Carol M. Cicerone Chair in Earth System Science. “We have found that large-scale changes in rainfall can, in part, be attributed to the way tropical forests respond to the overabundance of carbon dioxide humans are emitting into the atmosphere, particularly over dense forests in the Amazon and across Asia.”

A new study led by former UCI postdoctoral scholar Gabriel Kooperman and published today in Nature Climate Change, demonstrates that interactions between rainforests and rising CO2 levels will contribute to an asymmetrical pattern of rainfall change across the tropics.

In many aspects of Earth system science, the local effects of environmental factors can impact faraway regions through their influence on the circulation and movement of moisture within the atmosphere. The UCI-led group predict a similar cascade of events, beginning with stomata, small structures on the underside of leaves that open and shut in order for plants to take in the CO2 they need to grow – and that also release water vapor.

When more CO2 is present, these orifices do not open as widely, which reduces the amount of water evaporated into the atmosphere. According to the researchers, this small process at the plant level, multiplied across the rainforest, will cause changes in the atmosphere, affecting the way winds blow and the flow of moisture coming from the ocean.

“In many tropical forest regions, the moisture supplied by transpiration, which connects water underground at the root level directly to the atmosphere as it is pulled up to the leaves, can contribute as much as moisture evaporated from the ocean that rains back down at a given location – which is normal rainforest recycling,” said Kooperman, now an assistant professor of geography and atmospheric sciences at the University of Georgia.

Congratulations to Kooperman and colleagues on this important publication. Using sophisticated climate models and simulations to provide a better picture of the consquences of a changing global climate, the scientists show system-wide responses to environmental change. The systems lens provides for better understanding and hopefully for more urgency in the direction of mitigating policies. Great work.

Image: Tropical forest regions, from the study.