The average global temperature on Earth has increased by a little more than 1° Celsius (2° Fahrenheit) since 1880. Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade. 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.
Source: earthobservatory.nasa.gov
