People will always need to eat. World population continues to rise, while available cropland does not. If anything, global warming will gradually reduce it through droughts and floods. And cropland is being partly diverted to biofuels. We can increase yields with fertilizers but poorer countries cannot do this, and fertilizers use a lot of oil in manufacture. Grains long term look set to rise, though there will be short term dips in the supply demand balance.