The annual rainfall on Palmyra Atoll, at 6°N, is 444 centimetres; at 6°S, the total is only 114 centimetres. According to a new study, this imbalance is down to the transport of heat by the huge conveyor-belt current that sinks near Greenland, travels along the ocean bottom to Antarctica, and then rises and flows north along the surface.
‘It rains more in the Northern Hemisphere because it’s warmer,’ said the study’s lead author Dargan Frierson, of the University of Washington. ‘The question is: What makes the Northern Hemisphere warmer? And we’ve found that it’s the ocean circulation.’
Frierson’s team analysed data from NASA’s Clouds and the Earth’s Radiant Energy System (CERES) satellites and found that sunlight actually delivers more heat to the Southern Hemisphere. However, when they modelled the flow of heat around the oceans, they found that as the so-called ocean meridional overturning circulation carried water back to the Northern Hemisphere along the surface, it brought with it some 400 trillion watts of energy.
‘This is really just another part of a big, growing body of evidence that’s come out in the last ten or 15 years showing how important high latitudes are for other parts of the world,’ said Frierson.
This story was published in the December 2013 edition of Geographical Magazine