Images: NASA, public domain.
NASA has just published two world maps showing temperature anomalies in the decades starting in 1970 and 2000. Looking at those maps, it's pretty obvious that the planet is warming, especially closer to the poles.
According to an ongoing temperature analysis conducted by scientists at NASA's Goddard Institute for Space Studies (GISS), the average global temperature on Earth has increased by about 0.8°Celsius (1.4°Fahrenheit) since 1880. Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade.
The maps above show temperature anomalies, or changes, for 2000-2009 (top) and 1970-1979. The maps do not depict absolute temperature, but how much warmer or colder a region is compared to the norm for that same region from 1951-1980. That period was chosen largely because the U.S. National Weather Service uses a three-decade period to define "normal" or average temperature. The GISS temperature analysis effort began around 1980, so the most recent 30 years were 1951-1980. It is also a period when many of today's adults grew up, so it is a common reference that many people can remember. (source)
A Few Things to Keep in Mind
Remember, while the amount of warming might seem intuitively small to use (1.4 degree? bah), you have to remember that we're not talking about your living room but about the whole planet. The quantity of extra energy that needs to be trapped in the atmosphere to warm up the whole planet for even a few degrees on average over a decade is quite large. We must also remember that the warming is not equally distributed, so some areas might see little of it while others can see increases of many degrees. This makes a bigger difference in marginal regions (ie. permafrost that is now melting, etc).
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