During a famine, food prices will go up. He could chose to grow a crop that does better with less sunlight and less rain. With respect to the rain part, what these so-called climate experts conveniently leave out is a warmer planet actually has more precipitation and conversely a cooler planet actually gets less rain. Deserts are not caused because of excess heat but because of geography and air currents. There are also such things as cold deserts but they are not in the public imagination in the same way as hot deserts are even though they are just as common.

And even then, another easy way to starve a bunch of people is to buy up farm-land and then refuse to farm it. The US even sometimes pays farmers not to farm when there is an excess of a certain crop. If he can bribe the government to alter that policy in just the right way, he can get paid to not farm a crop for which there is a demand. And people would starve in the process.