President Donald Trump is withdrawing the United States from a foundational climate treaty and the world's leading global warming assessment body, as part of a sweeping exit from the United Nations system, the White House announced Wednesday.

A total of 66 international organizations were named in a White House memorandum as "contrary to the interests of the United States."

Most notable among them is the United Nations Framework Convention on Climate Change (UNFCCC), the parent treaty underpinning all major international climate agreements. 

Trump, who has thrown the full weight of his domestic policy behind fossil fuels, has openly scorned the scientific consensus that human activity is warming the planet, deriding climate science as a "hoax" at the UN's high-level summit last September.

The UNFCCC was adopted at the Rio Earth Summit in June 1992 and approved later that year by the US Senate during George H.W. Bush's presidency.

The US Constitution allows presidents to enter treaties "provided two thirds of Senators present concur," but it is silent on the process for withdrawing from them -- a legal ambiguity that could invite challenges.

Trump has already withdrawn from the landmark Paris climate accord since returning to office, just as he did during his first term, a move that Democratic president Joe Biden later reversed.

Exiting the underlying treaty could introduce additional legal uncertainty around any future US effort to rejoin.

"President Trump's withdrawal of the United States from the bedrock global treaty to tackle climate change is a new low and yet another sign that this authoritarian, anti-science administration is determined to sacrifice people's well-being and destabilize global cooperation," Rachel Cleetus of the Union of Concerned Scientists told AFP.

The memo also directs the United States to withdraw from the Intergovernmental Panel on Climate Change, the UN body responsible for assessing climate science, alongside other climate-related organizations including the International Renewable Energy Agency, UN Oceans and UN Water.

As in his first term, Trump has also withdrawn the United States from the Paris Agreement and from UNESCO -- the UN Educational, Scientific and Cultural Organization -- which Washington had rejoined under Biden.

Trump has likewise pulled the US out of the World Health Organization and sharply reduced foreign aid, slashing funding for numerous UN agencies and forcing them to scale back operations on the ground, including the High Commissioner for Refugees and the World Food Programme.

Other prominent bodies named in the memo include the UN Population Fund (UNFPA), which works on sexual and reproductive health and rights, and the UN Conference on Trade and Development (UNCTAD), which focuses on trade, investment and development.

Speaking before the General Assembly in September, Trump delivered a scathing broadside against the UN, saying it was "not even coming close to living up" to its potential.