Demonstrators hold banners during a rally near the Eiffel Tower in Paris on Dec. 12, 2015 on the sidelines of the COP 21, the UN conference on global warming. Credit: Francois Guillot/AFP via Getty Images Regardless of the outcome of the presidential election, the United States will officially be out of the 2015 Paris climate agreement on Nov. 4, marking a disappointing milestone in the international effort to stop global warming. Climate experts say that, if the world’s biggest historic greenhouse gas polluter won’t slash emissions, there’s little hope of meeting the Paris target of averting catastrophic global warming. But the U.S. could rejoin the global climate pact quickly, and Democratic presidential candidate Joe Biden has said he would do that early in his presidency. After sending a letter to the United Nations Secretary General, the United States would once again become a party to the Paris Agreement 30 […]