The Earth has been getting warmer -- but how much of that heat is due to greenhouse gas emissions and how much is due to natural causes? A leaked report by a United Nations’ group dedicated to climate studies says that heat from the sun may play a larger role than previously thought. “[Results] do suggest the possibility of a much larger impact of solar variations on the stratosphere than previously thought, and some studies have suggested that this may lead to significant regional impacts on climate,” reads a draft copy of a major, upcoming report from the U.N.’s Intergovernmental...