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Drastic changes ahead for the Earth's tropical rain belt

As Earth’s temperatures continue to rise, the tropical rain belt is expected to make a permanent shift to the north. A new study from UC Irvine confirms that climate change will alter the position of the rain belt, but reveals that the changes will be regionally inconsistent.

The interdisciplinary research team – consisting of environmental engineers, Earth system scientists, and data science experts – warns that the uneven shifting of the tropical rain belt could threaten food security for billions of people.

The tropical rain belt, a band of heavy rainfall near the equator, is known to migrate northward and southward with the seasonal movement of the sun.

The new study shows that the consistency of these annual migration patterns will be disrupted by climate change, and not all parts of the tropics will be affected equally.

For example, the rain belt will move north in parts of the Eastern Hemisphere, and south in parts in the Western Hemisphere.

According to the study authors, a northward shift of the tropical rain belt over eastern Africa and the Indian Ocean will result in future increases of drought stress in southeastern Africa and Madagascar. This climate pattern will also amplify flooding in southern India. 

Furthermore, as a result of the rain belt moving southward over the eastern Pacific and Atlantic Oceans, Central America will experience more intense drought conditions.

“Our work shows that climate change will cause the position of Earth’s tropical rain belt to move in opposite directions in two longitudinal sectors that cover almost two thirds of the globe, a process that will have cascading effects on water availability and food production around the world,” explained study lead author Antonios Mamalakis.

For the investigation, the experts analyzed computer simulations from 27 advanced climate models. They measured the tropical rain belt’s response to a scenario in which greenhouse gas emissions continue to rise through the end of the century.

Mamalakis said the sweeping shift detected in his work was disguised in previous modeling studies that provided a global average of the influence of climate change on the tropical rain belt. His team was able to predict the drastic upcoming changes by isolating the response in the Eastern and Western Hemisphere zones.

“In Asia, projected reductions in aerosol emissions, glacier melting in the Himalayas and loss of snow cover in northern areas brought on by climate change will cause the atmosphere to heat up faster than in other regions,” said study co-author James Randerson. 

“We know that the rain belt shifts toward this heating, and that its northward movement in the Eastern Hemisphere is consistent with these expected impacts of climate change.”

The weakening of the Gulf Stream current and deep-water formation in the North Atlantic is likely to have the opposite effect, causing a southward shift in the tropical rain belt across the Western Hemisphere, explained Randerson.

“The complexity of the Earth system is daunting, with dependencies and feedback loops across many processes and scales,” said study co-author Professor Efi Foufoula-Georgiou.

“This study combines the engineering approach of system’s thinking with data analytics and climate science to reveal subtle and previously unrecognized manifestations of global warming on regional precipitation dynamics and extremes.”

The study is published in the journal Nature Climate Change.

By Chrissy Sexton, Staff Writer

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