“There’s another challenge to building a climate consensus: Global cooperation is notoriously difficult. It’s hard to get every country in the world to agree on anything—especially when you’re asking them to incur some new cost, like the expense of curbing carbon emissions. No single country wants to pay to mitigate its emissions unless everyone else will too. That’s why the Paris Agreement, in which more than 190 countries signed up to eventually limit their emissions, was such an achievement. Not because the current commitments will make a huge dent in emissions—if everyone meets them, they’ll reduce annual emissions by 3 billion to 6 billion tons in 2030, less than 12 percent of total emissions today—but because it was a starting point that proved global cooperation is possible. The U.S. withdrawal from the 2015 Paris Agreement—a step that President-elect Joe Biden promised to reverse—only illustrates that it’s as hard to maintain global compacts as it is to create them in the first place.”