Trump should talk theoretically about questions asked by reporters.
When it comes to political issues he is involved with, he always says "That's hoax" or "That's fake news" without satisfying explanation.
If it's within the United States, it won't be a big issue. But, global warming is not an issue in the United States, but also the issue around the world.
So, it's not dependent on his responsibility. He shouldn't talk about it recklessly.