Hundreds of environmental organizations are asking President Obama to immediately stop selling new leases for extracting oil, natural gas and coal on federal land and water.

The green groups and individuals argue that an immediate halt to lease sales would avoid as much as 450 billion tons of planet-warming carbon dioxide from entering the atmosphere just as world leaders head to Paris in December to write a climate change pact.

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“The longstanding U.S. policy of leasing federal public lands and oceans to corporations for coal, oil and gas extraction must end,” the groups wrote in their Monday letter.

“As the world focuses on climate change in advance of negotiations in Paris this winter, we urge you to demonstrate strong climate leadership by stopping new leasing of our publicly owned fossil fuels.”

The letter is the latest indication that, while greens recognize Obama’s historic actions to fight climate change, including his highly controversial carbon limits for power plants, they don’t think he’s done enough to avoid the most catastrophic effects of global warming.

That anger was especially visible last month, when Obama visited Alaska amid protests over his approval of Royal Dutch Shell’s plan to drill for oil and natural gas in the Arctic Ocean.

And while Obama’s policies have focused mainly on how energy is consumed, the environmental activists are asking that he also take action to crack down the collection of fossil fuels.

The request also puts a great deal of blame for climate change solidly on Obama’s shoulders, arguing publicly owned fossil fuel resources are his responsibility.

“With the stroke of a pen, you could take the bold action needed to stop new federal leasing of fossil fuels, and to keep those remaining fossil fuels — our publicly owned fossil fuels — safely in the ground,” they said.

If Obama complied with the groups’ request, drilling would still be allowed on existing leases, which cover 67 million acres.