News Source: 
The Daily
October 23, 2013

A study recently published in the Nature Geoscience journal shows that ocean currents from the Earth’s poles are the reason why the northern hemisphere is warmer and rainier than the southern hemisphere.

The team included researchers from the UW, the University of Hawaii, Columbia University, the Massachusetts Institute of Technology, and Ulsan National Institute of Science and Technology in South Korea. They found that warmer places are wetter because the air rises more frequently, allowing its moisture to precipitate.

Dargan Frierson, a UW associate professor of atmospheric sciences, said that ocean circulation makes the northern hemisphere warmer.

Previously, scientists believed that the difference in the two hemispheres could be attributed to the Earth’s geometry. They believed that the diagonally tilting ocean basins pushed tropical rain north of the equator.

“At the same time, a lot of people didn’t really believe that explanation because it’s kind of a complicated argument,” Frierson said in an interview with UW Today. “For such a major feature, there’s usually a simpler explanation.”

Using satellites from NASA, the researchers discovered that sunlight provides more heat to the southern hemisphere, suggesting that the region should be soggier. They then used computer models to show how a massive conveyor-belt current travels and sinks near Greenland, moves along the ocean’s depths to Antarctica, and then rises to the ocean’s surface. As this water moves back north along the surface, it gradually heats up and carries approximately 400 trillion watts of power.