1) they are politicians who receive copious amounts of money from the industries who are responsible for much of the polluting that is causing climate change,
2) they are so deeply committed to their partisan political beliefs that they couldn't possibly admit Al "I invented the Internet (but never really said that, the media just keeps saying I did)" Gore and liberal f@#$ing hippies have been right
3) they find some sort of strange amusement in denying that most of the scientific evidence produced suggests the climate is changing and man's activities are a big reason for that, even as a good portion of Russia is on fire, a good bit of Pakistan is under water, and a nice big piece of Greenland four times the size of Manhattan is now floating around in the ocean, just looking for off-shore oil rigs to take out.
So, while, as a country we do very little to lead the rest of the world toward engaging in activities to help at least start to limit the harm we are doing, the impact of climate change on how the world eats is quickly making itself known:
Already the extreme drought and heat has badly damaged grain harvests in Russia, Kazakhstan and Ukraine, the old Soviet breadbasket responsible for one-fourth of the world's wheat exports. Russia's grain harvest could drop from 94 million tons to 65 million tons or less this year—an alarming figure that prompted Moscow to ban grain exports, steps that could be followed by its neighbors.