Even with the involvement of the U.S., the world’s second-largest producer of carbon dioxide emissions, the global response to climate change faced an uphill battle. Then President Donald Trump pulled the U.S. out of the Paris Agreement on global warming. The threat of climate change presented one of the starkest contrasts between Trump and Joe Biden in the 2020 presidential race. Now, after winning the election, Biden will get a chance to see through his pledge to sign the U.S. back into the Paris accord as soon as he can.

1. What’s the Paris Agreement?

The 2015 accord among almost 200 countries brought together the developed and developing worlds to pledge limits on the fossil-fuel pollution that causes climate change. Those pledges are voluntary and non-binding. The goal is to hold the rise in temperatures to below 2 degrees Celsius (compared with preindustrial levels), and preferably to 1.5 degree, at the end of this century, to avoid the rising seas and superstorms that climate models predict.

2. When did the U.S. leave the agreement?

After giving one-year written notice, the U.S. withdrawal took effect on Nov. 4, the day after the presidential election.

3. What will Biden do?

He said he would apply to rejoin on his first day as president and then “lead an effort to get every major country to ramp up the ambition of their domestic climate targets.” There would be a 30-day waiting period for the U.S. re-entry to take effect.

4. Has the Paris agreement helped slow global warming?

Not enough so far. Human activities are estimated to have already caused about 1 degree Celsius of warming and are increasing at a rate of about 0.2 degrees Celsius per decade. The UN World Meteorological Organization has said that global temperatures are on track to rise 3 to 5 degrees by the end of this century, well beyond the targeted cap of 2 degrees. The years 2015 to 2019 were the warmest five years on record, and 2010 to 2019 was the warmest decade on record, according to the UN agency. Climate Action Tracker, a research project, agrees that current policies and pledges will leave the planet “well above” the Paris accord’s “long-term temperature goal.” Even with the U.S. involved, academics were concerned that the world was headed for “extensive” species extinctions, serious crop damage and irreversible increases in sea levels.

5. What did the U.S. pledge under the Paris agreement?

To cut its carbon dioxide emissions 26 to 28 percent from 2005 levels by 2025. In addition, the U.S. was being counted on to contribute heavily to a Green Climate Fund that helps poorer nations invest in renewable energy. The fund is falling short of its target, with the U.S. halting payments in 2017 and Australia forswearing new contributions in December 2019.

6. What was Trump’s gripe with the agreement?

He’s called the pact “a total disaster for our country” that would hurt American competitiveness by enabling “a giant transfer of American wealth to foreign nations that are responsible for most of the word’s pollution.” He says rules and directives put in place by his predecessor, Barack Obama, to meet the U.S. targets for emissions hurt the U.S. economy by killing jobs related to fossil fuels, especially coal mining. And he’s dismantled Obama-era regulations meant to stifle greenhouse gas emissions from power plants, automobiles and oil wells.

7. Does Trump believe humans cause global warming?

That’s a long story. Trump mocked global-warming fears as a “hoax” before taking office, and as a candidate he promised to focus on “real environmental challenges, not the phony ones we’ve been looking at.” He ridiculed renewable power -- wind and solar and the like -- as “just an expensive way of making the tree-huggers feel good about themselves.” Trump has softened some of those views, saying in 2018 that while he doesn’t think it’s a hoax, he isn’t sure climate change is a “man-made” phenomenon. More recently, on Sept. 14, in a meeting at which a California official urged him “to really recognize the changing climate and what it means to our forests,” Trump replied, “It’ll start getting cooler, you just watch.” When the official pointed out science doesn’t say that, Trump responded, “I don’t think science knows, actually.”

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