Last year was the ninth warmest on record, and nine of the 10 warmest years in the modern meteorological record have occurred since 2000, according to a new analysis from NASA that compares temperatures to the mid-20th-century average. The only year among the top-10 warmest from the 20th century is 1998. Last year was marked by two factors that should have brought temperatures slightly down -- La Nina and low solar activity -- but despite these it was one of the warmest on record.
Higher temperatures today are the result of higher concentrations of greenhouse gases, particularly carbon dioxide. In 1880, when the study's temperature record-keeping begins, the concentration of carbon dioxide was 285 parts per million. Today it is more than 390 parts per million and rapidly increasing. Many top climate scientists, including NASA's James Hansen, have argued that a level not exceeding 350 parts per million is necessary "if humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted."
The above graph shows the difference between the annual average temperature and a baseline drawn from 1951 to 1980. The video below shows the geographic distribution of the changing temperatures. Blues indicate temperatures below the baseline and reds indicate temperatures above.
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