How the Global Ocean Conveyor-Belt Impacts Northern Hemisphere Precipitation

A quick glance at the world precipitation map shows that most tropical rain falls in the Northern Hemisphere.  Yet as our climate continues to change, these weather patterns may soon be impacted. It turns out that ocean currents originating from the poles thousands of miles away may influence this precipitation, which means changes to these currents could greatly impact where and when rain falls.

"It rains more in the Northern Hemisphere because it's warmer," said Dargan Frierson, one of the researchers, in a news release. "The question is: What makes the Northern Hemisphere warmer? And we've found that it's the ocean circulation."

The precipitation in this region is crucial for growing crops. More specifically, Africa's Sahel region and southern India rely heavily on the seasonal rains that fall in the area. If these rain patterns were to stop or shift, there could be massive issues for the farmers in these regions.

In order to learn a bit more about what might impact these rain patterns and make the region warmer, the researchers used detailed measurements from NASA's Clouds and Earth's Radiant Energy System, or CERES, satellites. This showed that sunlight actually provides more heat to the Southern Hemisphere. In theory, this would make the Southern Hemisphere wetter than the north. Obviously, though, that's not the case.

The scientists then used computer models to show the key role of the huge conveyor-belt current that sinks near Greenland in the world's oceans. This current then travels along the ocean bottom to Antarctica where it then rises and flows north along the surface. The researchers found that eliminating this current actually flips the tropical rain bands to the south. As the water moves north over many decades, it gradually heats up. This carries about 400 trillion watts of power across the equator.

In addition, the researchers found that a gradual slowing of this current would be very likely by 2100. This, in turn, could shift tropical rains south, which would mean drastic changes for several regions in the Northern Hemisphere.

"This is really just another part of a big, growing body of evidence that's come out in the last 10 or 15 years showing how important high latitudes are for parts of the world," said Frierson in a news release.

The findings reveal exactly what current is responsible for these seasonal rainfall patterns. In addition, it reveals that climate change could impact the flow of this current and could, in turn, affect rainfall patterns.

The findings are published in the journal Nature Geoscience.