USA Today: Campaign ads are attacking U.S. senators for their positions on energy and climate change as the 2010 election season intensifies and President Obama pushes a broad climate bill. Americans United for Change, a group promoting progressive causes, announced a $400,000 TV ad campaign this week criticizing GOP Sens. Scott Brown of Massachusetts, Chuck Grassley of Iowa and Richard Burr of North Carolina. You can watch one above or by clicking here. The Republicans voted last week …