U.S. Environmental Protection Agency Director Lisa Jackson announces a new Obama administration position that greenhouse gasses are a threat to public health at the EPA in Washington, December 7, 2009. REUTERS/Jonathan Ernst  By Timothy Gardner

WASHINGTON, Dec 7 (Reuters) – The U.S. Environmental Protection Agency on Monday cleared the way for regulation of greenhouse gases without new laws passed by Congress, reflecting President Barack Obama’s commitment to act on climate change as a major summit opened in Copenhagen.