President Trump is having a large and dramatic impact during his first half-year in office. A major turning point in U.S. environmental policy came last week when he kept a campaign pledge by withdrawing from a worldwide climate agreement negotiated in Paris in December 2015. The move defies pleas from allies such as France, Germany, the United Kingdom and others that urged Trump to remain a part of efforts to halt the planet's rising average temperatures. Scientists link greenhouse gases from burning fossil fuels (oil, gasoline, coal) to dangerous warming that raises ocean levels, affects agriculture and endangers living creatures.

"I was elected to represent the citizens of Pittsburgh, not Paris," Trump said in the White House Rose Garden. Nearly 200 United Nations members have signed the agreement and 148 have ratified it. It takes effect in 2020, but doesn't force nations to set specific targets or timetables. Each country determines its own contribution to ease global warming. There's some oversight and accountability, but no penalties. The idea is to create a coalition of cooperation, using public attention and peer pressure to get countries to step up their climate game.

The Paris agreement provides a structure to protect everyone by increasing use of alternative energy sources (such as wind and solar power) and cleaner-burning fuels for vehicles, factories, homes and offices. Now that the world’s largest economy pulls out, the big question is whether others will press ahead with climate action anyway, led by Europe and China, or whether the accord start to unravels. “He has certainly made the world safe for Chinese influence,” says Richard Haass, president of the Council on Foreign Relations, a private group in Washington, D.C. It's also worth noting that America's withdrawal formally takes effect Nov. 4, 2020, a day after the next presidential election. So if Trump doesn't seek and win a second term, the next White House occupant could rejoin the coalition he's leaving.

President says: "This agreement is less about the climate and more about other countries gaining a financial advantage over the United States. . . We would find it very hard to compete."

Critic says: "Climate change is real. Leaving Paris [agreement] is not good for America or the world." – Tweet by tech executive Elon Musk, who quit White House advisory council

Supporter says: "The president here has made good on his promise to put America first." – Editorial in the National Review, a conservative magazine