Climate change to shift tropical rains north, computer modeling suggests

A study led by a UC Riverside atmospheric scientist predicts that unchecked carbon emissions will force tropical rains to shift northward in the coming decades, which would profoundly affect agriculture and economies near Earth’s equator.

The northward shift of rain will be caused by complex changes in the atmosphere driven by carbon emissions that affect the formation of intertropical convergence zones. Those areas are essentially atmospheric engines that drive about a third of the world’s precipitation, Liu and his coauthors report in a paper published June 28 in the journal. Climate change in nature. The title of the paper is “Contrast of fast and slow migrations of intertropical convergence zones associated with delayed warming of the Southern Ocean”.

Tropical regions on either side of the equator, such as the nations of central Africa, northern South America and the Pacific island states, among other regions, will be the most affected. Major crops grown in the tropics include coffee, cocoa, palm oil, bananas, sugarcane, tea, mangoes and pineapples.

However, the northward shift will only last for about 20 years before larger forces stemming from the warming of the southern oceans pull the convergence zones back southward and hold them there for another millennium, Wei Liu said. an associate professor of climate change and sustainability in the UCR College. Natural and Agricultural Sciences.

Intertropical convergence zones are areas along or near the equator where trade winds from the northern and southern hemispheres meet and blow up at cooler altitudes, absorbing large volumes of moisture from the oceans. As this moist air cools at higher elevations, thunderclouds form, allowing for heavy rainstorms. Tropical rainforests can receive up to 14 feet of rain per year.

“The change in precipitation is very important,” Liu said. “It is a region with very high rainfall. So a small shift will cause big changes in agriculture and the economy of societies. It will affect many regions.”

Liu and his colleagues used sophisticated computer models to predict the atmospheric impact of carbon dioxide emissions from the continued burning of fossil fuels and other sources, Liu said.

“This climate model involved many components of the atmosphere, ocean, sea ice and land. All of these components are interacting with each other,” he said. “Basically, we try to simulate the real world. In the model, we can increase our carbon dioxide emissions from pre-industrial levels to much higher levels.”

The analysis calculated how carbon emissions affect the amount of radiant energy at the top of the atmosphere. It also considered changes in sea ice, water vapor and cloud formation. These and other factors resulted in conditions pushing the rain-forming convergence zones northward by 0.2 degrees on average.