http://earthobservatory.nasa.gov/Features/WorldOfChange/decadaltemp.php?src=eoa-features
A snapshot of Earth over the past 130 years with heating and warming trends.
“A one-degree global change is significant because it takes a vast amount of heat to warm all the oceans, atmosphere, and land by that much. In the past, a one- to two-degree drop was all it took to plunge the Earth into the Little Ice Age. A five-degree drop was enough to bury a large part of North America under a towering mass of ice 20,000 years ago. ”