When Trump announced the U.S. withdrawal from the climate agreement in 2017, the move reverberated around the globe. Nearly 200 nations had committed to reducing greenhouse gas emissions under the pact when it was created in 2015, and they had set ambitious targets to keep global temperature rise well below 2°C, and ideally below 1.5°C.

U.S. withdrawal from the world's primary climate pact will have a bigger impact - in the U.S. and globally - than the country's first retreat in 2017, analysts and diplomats told Reuters.