Governor John Baldacci signed a landmark global warming law Monday that puts Maine on track to be part of the nation’s first regional effort to reduce greenhouse gas emissions.

The law, “An Act To Establish the Regional Greenhouse Gas Initiative Act of 2007,” creates a system to limit carbon dioxide emissions from large power plants in Maine by requiring companies to pay for allowances to pollute. Power plants will then be able to buy and sell the credits, creating an incentive to reduce emissions.

Maine is one of 10 Northeast states participating in the cap-and-trade system. The states have agreed to freeze power plant emissions from 2009 to 2015 and cut them 10 percent by 2019.

Signing the law is the latest in a series of steps taken against global warming, according to the Baldacci administration.

Since 2002, Maine has reduced its greenhouse gas emissions by 8 percent, the governor’s office said. Maine is the first state government in the nation to buy 100 percent of its electricity from renewable sources, it said.