1) In the Paris Agreement of 2015, participating countries agreed to reduce greenhouse gas emissions and regularly increase their ambitions to do more to address manmade climate change. It sets an overall goal of limiting the increase in global average temperatures to less than 2 degrees centigrade (3.6 degrees Fahrenheit).

2) It is nonbinding, meaning there are no penalties attached for failing to meet reductions.

3) To date, 195 participating countries have signed on to develop their own emissions reduction targets. President Obama's Clean Power Plan, for instance, sought to reduce U.S. greenhouse gas emissions from 2005 levels by 32 percent by 2030. President Trump already signed an executive order in March to unravel the Obama action.

4) With Trump's action Thursday, the U.S. joins Nicaragua and Syria as the only countries not participating in the Paris Agreement. Trump said he would immediately seek to renegotiate the accord, which he called more onerous on the U.S. than other countries. France, Germany and Italy immediately issued a joint statement saying there would be no negotiation.

5) The president objected to the accord's "green climate fund" that would go to help developing countries meet their goals.  He said the U.S. has already contributed $1 billion and the fund will cost "a vast fortune."