Take away 75% for the oceans and lakes. Take away another 12.5% for the polar ice caps, deserts, swamps, and mountains. And then another 9.5% for land that is too rocky, too wet, too steep, or too cold. That leaves only 3% of all the available area on the Earth for agriculture! This small parcel of land is all that farmers have available to feed, clothe, and fuel our growing population.