WASHINGTON – Three competing Senate proposals calling for limits on greenhouse gases would have roughly identical success in curbing global warming, but only if other nations also significantly cut heat-trapping emissions, a government analysis says.

The Environmental Protection Agency examined the long-term impact of three climate change bills being considered in the Senate, each of which would cap carbon dioxide emissions from cars, industry and power plants with a goal of reducing greenhouse gas releases by 60 percent to 65 percent by midcentury.

By the end of the century, all three bills would have reduced the concentration of carbon dioxide in the atmosphere by roughly the same amount – about 23 to 25 parts per million, said the EPA report, which was sent Tuesday to Capitol Hill.

“The three bills achieve similar levels of cumulative [greenhouse gas] emissions abatement,” the EPA wrote in letters to Sens. Jeff Bingaman, D-N.M., and Arlen Specter, R-Pa., co-sponsors of one bill.

Of the other bills, one was proposed by Sens. Joe Lieberman, a Connecticut independent, and Arizona Republican Sen. John McCain, who is running for president, and the other was proposed by Sens. John Kerry, D-Mass., and Olympia Snowe, R-Maine.