UNITED NATIONS (AP) — The United Nations secretary-general said the world must dramatically change the way it fuels factories, vehicles and homes to limit future warming to a level scientists call nearly impossible.

That’s because the alternative “would mean a catastrophic situation for the whole world,” António Guterres told The Associated Press in an exclusive interview.

Guterres said he’s about to tour Pacific islands to see how climate change is devastating them as part of his renewed push to fight it. He is summoning world leaders to the U.N. in September to tell them “they need to do much more in order for us to be able to reverse the present trends and to defeat the climate change.”

That means, he said, the world has to change, not in small incremental ways but in big “transformative” ways, into a green economy with electric vehicles and “clean cities.”

Guterres said he will ask leaders to stop subsidizing fossil fuels. Burning coal, oil and gas triggers warming by releasing..