The move, long advanced by US President Donald Trump and triggered by his administration a year ago, further divides Washington in the world but has no instant impact on international efforts to curb global warming.
There are 189 countries that remain accepted with the 2015 Paris accord, which strives to keep the increase in average temperatures worldwide “well below” 2 degrees Celsius (3.6 degrees Fahrenheit), ideally no more than 1.5C (2.7 F), compared to pre-industrial levels. A further six countries have signed, but not ratified the pact.
Scientists say that any increase beyond 2 degrees Celsius could have a disastrous impact on large parts of the world, rising sea levels, causing tropical storms and worsening droughts and floods.
The Paris accord requires countries to set their own voluntary targets for diminishing greenhouse gases such as carbon dioxide. The only binding element is that nations have to carefully report on their efforts.
The United States is the world’s second-biggest emitter after China of heat-trapping gases such as carbon dioxide and its offering to cutting emissions is seen as important, but it is not alone in the effort. In recent weeks, China, Japan, and South Korea have joined the European Union and several other countries in setting national deadlines to stop drawing more greenhouse gases into the atmosphere.
Democratic presidential candidate Joe Biden has said he supports signing the US back up to the Paris accord.
The German government said it was “highly regrettable” that the United States had left the pact.
“It’s all the more important that Europe, the EU and Germany lead by example,” said government spokesman Steffen Seibert, indicating the EU’s goal of becoming the first climate-neutral continent by 2050.
While the Trump presidency has avoided federal measures to cut emissions, Seibert noted that US states, cities and businesses have pressed ahead with their own efforts.
"The lack of action at the federal level is a serious problem," says Rachel Cleetus, policy director for the climate and energy program at the Union of Concerned Scientists, a science advocacy group. The costs of climate-driven disasters such as hurricanes, heat waves and wildfires are rising, she says. In 2020, there have already been 16 climate-driven disasters that cost at least $1 billion each, according to the National Oceanic and Atmospheric Administration.
"Climate change is clearly not just an environmental issue," Cleetus says. "It is threatening our economy. It's threatening our future prosperity, the well-being of future generations."