Hundreds of scientists and policy experts sent a letter to President Donald Trump asking him to withdraw from a major United Nations environmental treaty ratified during the Bush administration.

More than 300 eminent scientists signed the letter to Trump, delivered Thursday, arguing he should pull out of the UN Convention on Climate Change (UNFCCC) because it targets carbon dioxide — a gas essential for life.

CO2 “is not a pollutant but a major benefit to agriculture and other life on Earth,” reads the petition, obtained by The Daily Caller News Foundation. “Observations since the UNFCCC was written 25 years ago show that warming from increased atmospheric CO2 will be benign — much less than initial model predictions.”

Trump promised to pull out of the Paris agreement on global warming, which went into effect in November 2016. President Barack Obama signed the U.S. up to cut greenhouse gases 26 to 28 percent.

The hundreds of scientists who signed the letter, however, argue that’s not far enough. Trump should pull out of the foundational treaty the Paris agreement is based on — the UNFCCC.

The UNFCCC’s focus on global warming is misguided because it targets CO2, which isn’t a pollutant, with the idea reducing it can stop global warming. Their plans aren’t supported by science, one petitioner argued in a letter.

“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,” reads a separate letter written by Richard Lindzen, a climatologist at the Massachusetts Institute of Technology (MIT).

“While we support effective, affordable, reasonable and direct controls on conventional environmental pollutants, carbon dioxide is not a pollutant,” Lindzen wrote in his letter, supplementing the petition.

“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,” Lindzen wrote.

Increasingly, scientists are finding the world has actually greened in the past few decades largely due to increased CO2 emissions into the atmosphere. CO2 fertilization is even greening some of the world’s most arid regions.

It’s not clear when Trump plans on withdrawing from the Paris agreement, but some sources say executive orders on the matter could be coming in the next few weeks.

Obama never brought the Paris agreement before the Senate for ratification, so Trump can treat it as an executive agreement, rather than a treaty, and pull out without congressional consent.

Pulling out of the UNFCCC may be trickier. The Senate ratified the UNFCCC in 1992, and there’s not a ton of legal precedent on what the procedure would be for withdrawing from such a treaty.

The petition from Lindzen and others comes just two months after a group of 800 scientists called on Trump to stay party to the Paris agreement. Those scientists claim pulling out of Paris would “undermine our best chance to avoid dangerous climate change.”

“The United States will lose its seat of influence at the international negotiating table, and will cede to China, the EU, and other countries its authority as a political, technological, and moral leader,” scientist wrote to Trump in December.

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