FACTBOX: U.S. state leadership on greenhouse gas limits

(Reuters) - U.S. states have led the federal government in setting limits on emissions of the gases most scientists blame for global warming.

The states have agreed to set up market mechanisms, such as cap-and-trade programs, that would reward polluters for cutting emissions. Some of their plans would work with Canadian provinces.

Several of the states were set to meet in Connecticut on Friday to broaden their fight against climate change.

President George W. Bush, who will step down in January, has long opposed tough emissions cuts, believing they would harm the economy. On Wednesday, Bush unveiled a plan to halt the growth of U.S. emissions by 2025.

The move was seen by many international politicians as too weak to slow potentially catastrophic climate change as many industrialized countries have already been trying to cut emissions. By many counts, the United States is the world's top greenhouse gas emitter.

Below is list of regional emissions reductions pacts agreed to by U.S. states:

Regional Greenhouse Gas Initiative (RGGI).

--Formed in 2005, and eventually signed by 10 states in the East.

--Members: Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, and Vermont.