Human influence on global temperature continued in 2011 (seen here). NASA scientists said the year was the ninth warmest on record.
Even with the complexities of climate change, scientists still take the planet's pulse with a basic benchmark measurement—temperature. The world has experienced nine of the 10 warmest years on record since 2000. And in 2011, the ninth warmest year since 1880, the average temperature was nearly a full degree warmer (0.92 Fahrenheit) than the 1951-1980 average, which is used as a baseline for comparison. Scientists at NASA's Goddard Institute for Space Studies compute Earth's long-term temperature trend by analyzing readings from thousands of ground-based weather stations and sea surface temperature data from ships and satellites. Earth's long-term warming trend remains driven primarily by an unprecedented increase in carbon dioxide levels in the atmosphere, created largely by increased fossil fuel burning for generating electricity and powering cars. That rate of increase has overwhelmed the prior, slow pace of atmospheric changes between geologic eras. Watch in the visualization below how temperatures across the globe have crept upward since the late 19th century.