Nine states agreed on a plan Wednesday to reduce carbon dioxide emissions by 30 percent between 2020 and 2030.

Member states of the Regional Greenhouse Gas Initiative agreed to cap carbon dioxide emissions and trade any excess emissions in auctions. The pact includes New York, Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, Rhode Island, and Vermont.

Under the plan, regional emissions will be capped at about 78.2 million tons of carbon dioxide per year in 2020 and be reduced to roughly 55.7 million tons in 2030. That 2030 goal represents a 65-percent drop from 2009 levels, the year the Regional Greenhouse Gas Initiative was created, the group said.

"RGGI states are demonstrating our commitment to a strengthened RGGI program that will utilize innovative new mechanisms to secure significant carbon reductions at a reasonable price on into the next decade, working in concert with our competitive energy markets and reliability goals," said Katie Dykes, chairwoman of the Regional Greenhouse Gas Initiative's board. Many scientists blame carbon dioxide and other greenhouse gases emitted from burning fossil fuels for driving manmade climate change.

Environmental groups who oppose the Trump administration's energy policies cheered the new plan.

President Trump in June announced his intent to remove the U.S. from the global Paris climate change accord, under which the Obama administration pledged to reduce emissions 26 percent to 28 percent below 2005 levels by 2025.

"In the face of the Trump administration's ongoing attempts to undermine solutions to climate change, nine governors – Republicans and Democrats alike – doubled down on a clean energy future for their citizens," said Rhea Suh, president of the Natural Resources Defense Council. "RGGI's bold plan will significantly cut power plant pollution while creating new benefits to the economy and people's health. Within the past month, California and the RGGI states have shown the world there are still climate leaders here in the U.S. Now we need other state, city, and federal officials to follow suit."

The Regional Greenhouse Gas Initiative will accept public comment on the plan at a Sept. 25 meeting in Baltimore.