Overlooked in the chaotic battle for the White House, the United States on the day after the presidential election officially left the Paris climate change agreement.
With millions voting for climate-change denier Donald Trump, the United States abandoned the global commitment to reduce carbon emissions.
Trump announced in July 2017 that the United States would leave the 2015 pact that seeks to limit global temperatures. But the treaty required a three-year waiting period for a country to withdraw.
If Trump takes back the White House, the United States, with 15 percent of global greenhouse emissions, will commit itself further to promoting fossil fuels.
Trump has relentlessly reversed President Obama's climate change efforts, from weakening auto-emissions regulations to promoting the coal and petroleum industries.
He has also begun steps to open petroleum drilling in Alaska's Arctic Wildlife Refuge and other long protected wilderness areas.
Democratic candidate Joe Biden, near a presidential victory, promises to return to the Paris agreement. If Biden is elected, the country would have a month to rejoin the treaty.
Biden calls for a massive effort to make buildings more energy efficient and developing wind and solar power to shift from a carbon-based economy.
The treaty seeks to keep global temperature increases this century to under 2 degrees celsius above pre-industrial averages. It calls for additional efforts to reach a 1.5c threshold.
Climate change has already advanced further than earlier projections, with soaring temperatures, drought, melting arctic ice, fires and hurricanes. Rising ocean levels will threaten coastal nations and cities.
The United States must rejoin the effort to reduce emissions if the world is to have any chance to limit climate change's devastation.