LiveScience: The Earth’s seasons have shifted back in the calendar year, with the hottest and coldest days of the years now occurring almost two days earlier, a new study finds. This shift could be the work of global warming, the researchers say. To figure this out, scientists at the University of California, Berkeley and Harvard studied temperature data from 1850 to 2007 compiled by the University of East Anglia’s Climate Research Unit in the United Kingdom. They found that …