Warming in the South Seas means wet west coast

As global temperatures warm, the southern oceans between Antarctica and other continents ultimately release heat absorbed from the atmosphere, predicting long-term increases in precipitation in East Asia and the western United States, regardless of climate mitigation efforts.

These teleconnections between the tropical Pacific and distant regions have been reported in a Cornell University-led computer model study published in Nature Geoscience.

Other computer models predict similar increases in precipitation generated by the warming Southern Ocean, but there is significant uncertainty and wide range of predictions between the models.

This new study can help reduce these uncertainties and improve forecasts of global average temperatures and local precipitation.

“We had to find the source of these uncertainties,” said Han Jun Kim, a postdoctoral associate who works with co-authors Flavio Lehner and Angeline Pendergrass, both associate professors of atmospheric science at Cornell. Sarah Kang, professor at the Max Planck Meteorology Institute in Hamburg, Germany, is another corresponding author of the paper.

“We found that low-altitude cloud feedback over the Southern Hemisphere could be one of the causes of those uncertainties in regional precipitation in the remote Northern Hemisphere,” Kim said. “Trying to reduce the uncertainty of cloud feedback in the Southern Hemisphere can also improve global average temperature forecasts.”

“Our study is the first study to show the exact routes that this upcoming change in the South Sea will affect weather patterns around the world, focusing specifically on these two regions in Asia and North America,” Liner said.

When the atmosphere warms, the oceans absorb heat and are eventually released into the atmosphere. The Southern Ocean has a greater ability to absorb heat than other bodies of water due to strong deep, cold water springing up, but in the end the water warms and gradually releases heat. When this occurs, the heat is distributed and a teleconnection is created. This is predicted to increase precipitation in East Asia during the summer and winter. Such communications are very similar to how El Niño influences weather patterns.

The model predicted that new precipitation patterns could last up to 150 years, regardless of efforts to reduce greenhouse gases due to slow ocean heat.

“We can see these processes today, and this allows us to study them,” Leaner said.

Kim discovered that low clouds in the South Sea act as a key regulator that affects sea surface temperature. Considering these cloud feedback in climate models, research has shown that it can help explain uncertainty and variation from one model to another.

With few Antarctic observation facilities, Kim said increasing them would improve forecasts as it provides data on cloud feedback in the south.