By Jeff Mason ABOARD AIR FORCE ONE (Reuters) -U.S. President Joe Biden will unveil new executive steps to address climate in a visit to Massachusetts on Wednesday that are expected to fall short of declaring the federal emergency many Democrats had urged. Democratic lawmakers and environmental groups have been calling for the White House to take aggressive measures on climate change after conservative Democratic Senator Joe Manchin said last week he was not ready to support key climate provisions in Congress, a critical loss in the evenly divided Senate. In a visit to Somerset, Massachusetts, …