One of the country's largest builders of coal-fired power plants will give investors detailed warnings about the risks that global warming poses to its business under a deal with New York's attorney general. The agreement Wednesday between the attorney general, Andrew M. Cuomo, and the company, Xcel Energy of Minneapolis, is the first of its kind in the country. It could open a broad new front in efforts by environmental groups to pressure the energy industry into reducing emissions of the greenhouse gases that contribute to global warming. Until now, advocates have largely relied on shareholder resolutions as a way of pushing the companies to reduce their carbon dioxide output and invest more aggressively in renewable energy sources like wind or solar power. That effort has picked up pace, according to Ceres, a coalition of investors and environmental groups, with dozens of shareholder resolutions filed during the 2008 financial reporting season. "This really takes it another step, by making it a settlement agreement that should have an impact across the industry,' said Dan Bakal, the director of electric power programs at Ceres. Mr. Cuomo subpoenaed Xcel and four other companies last September, seeking to determine whether their efforts to build new coal-fired power plants posed risks not disclosed to investors, like future lawsuits or higher costs to comply with possible regulations restricting carbon emissions. The attorney general's office is still negotiating with the four other companies