The US has issued the first written notification that it intends to withdraw from the 2015 Paris climate agreement.
However, in the notice to the UN, the US State Department said Washington would remain in the talks process.
President Donald Trump drew international condemnation in June when he first announced the US intention to withdraw.
Donald Trump said the deal “punished” the US and would cost millions of American jobs.
August 4 announcement is seen as largely symbolic as no nation seeking to leave the pact can officially announce an intention to withdraw until November 4, 2019.
The process of leaving then takes another year, meaning it would not be complete until just weeks after the US presidential election in 2020.
Any new US president could then decide to rejoin the agreement.
The US statement read: “Today, the United States submitted a communication to the United Nations in its capacity as depositary for the Paris Agreement regarding the US intent to withdraw from the Paris Agreement as soon as it is eligible to do so.
“The United States will continue to participate in international climate change negotiations and meetings… to protect US interests and ensure all future policy options remain open to the administration.”
Two months ago, President Trump indicated he was open to another climate deal “on terms that are fair to the United States”.
However, key signatories to the accord quickly ruled that out. The Paris Agreement took decades to finalize.
The US stance on climate change also caused divisions at the G20 summit in Germany in July.
A joint summit statement said it “took note of the decision of the United States of America to withdraw from the Paris Agreement”.
However, leaders of the other G20 members agreed the accord was “irreversible”.
Climate change, or global warming, refers to the damaging effect of gases, or emissions, released from industry, transportation, agriculture and other areas into the atmosphere.
The Paris Agreement aims to limit the global rise in temperature attributed to emissions. Only Syria and Nicaragua did not sign up.
NASA’s Goddard Institute for Space Studies says the world’s average temperature has risen by about 0.8C since 1880, two-thirds of that since 1975.
US think tank Climate Interactive predicts that if all nations fully achieve their Paris pledges, the average global surface temperature rise by 2100 will be 3.3C, or 3.6C without the US.