About half of the world's wetlands area is found in the tropics. The importance of wetlands to the global carbon cycle, water balance, wildlife, biodiversity and human food production is much greater than their proportional surface area on Earth (7%) would suggest. High net primary production of organic matter produced by retarded decomposition make natural tropical wetlands an important sink for carbon. About 250 Gt carbon are conserved in tropical wetlands. Tropical wetlands are also a significant source for atmospheric methane. Wetland rice agriculture alone contributes 5 to 20% to the global methane budget. Rice, the stable food for about half of mankind, is grown on tropical wetlands. Small differences in climate, water and nutrient regimes, and land use can drastically change the delicate balance of tropical wetlands.