A quick glance at a world precipitation map shows that most tropical rain falls in the Northern Hemisphere. Scientists long believed that this was a quirk of Earth's geometry -- that the ocean basins tilting diagonally while the planet spins pushed tropical rain bands north of the equator. But a new study shows that the pattern arises from ocean currents originating from the poles, thousands of miles away. The findings, published Oct. 20 in Nature Geoscience, explain a fundamental feature of the planet's climate, and show that icy waters affect seasonal rains that are crucial for growing crops in such places as Africa's Sahel region and southern India....