A group of scientists and others skeptical of global warming are asking President Trump to withdraw the United States from the United Nations’ climate change agency.

The group of 300, led by high-profile climate change skeptic Richard Lindzen, said in a Thursday letter to Trump and Vice President Pence that greenhouse gases like carbon dioxide are not as harmful as most climate scientists say.

“Since 2009, the US and other governments have undertaken actions with respect to global climate that are not scientifically justified and that already have, and will continue to cause serious social and economic harm — with no environmental benefits,” the letter reads.

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“While we support effective, affordable, reasonable and direct controls on conventional environmental pollutants, carbon dioxide is not a pollutant,” it says. “To the contrary, there is clear evidence that increased atmospheric carbon dioxide is environmentally helpful to food crops and other plants that nourish all life. It is plant food, not poison.”

The U.N.’s Framework Convention on Climate Change is an international treaty that was established in 1992 and signed by more than 150 countries. The treaty requires countries to make certain annual disclosures about their greenhouse gas emissions, among other requirements.

It is under the treaty that leaders in 2015 wrote the Paris agreement, which includes non-binding emissions reductions.

Trump has vowed to “cancel” the Paris agreement. But shortly after the November election, Reuters reported that some advisers were exploring a pullout from the 1992 treaty altogether.

While the signers of the Thursday letter differ slightly on their exact problems with mainstream climate science, Lindzen has argued that the atmosphere is not as sensitive to carbon dioxide as most believe, due to other factors that counteract its greenhouse effect.

“It is especially important for members of your administrative team to hear from people like the signers of this letter, with the training needed to evaluate climate facts, and to offer sound advice,” the signers wrote. “Climate discussions have long been political debates — not scientific discussions — over whether citizens or bureaucrats should control energy, natural resources and other assets.”