According to research led by James Hansen of NASA's Goddard Institute for Space Studies in New York, the earth has been warming at a rate of 0.36 degrees Fahrenheit each decade for the past 30 years, which has driven the overall temperature to the warmest in 12,000 years.
A recent report in the journal Nature found that global warming had driven 1,700 plant, animal and insect species to move toward the planet's poles at roughly 4 miles per decade over the last half of the 20th century. Global warming has been strongest in the far north, where melting snow and ice have exposed dark-colored land that absorbs more warmth from the sun than water, which has sped warming.
The researchers also note marked warming in the Indian and western Pacific Oceans, both of which have major impacts on climate. Changes in the water temperature in those oceans could lead to more El Nino-like weather episodes.
Though most scientists agree that the planet has warmed, not all concur on the cause of the warming. Hansen believes the most dominant factor in climate change has been human-made greenhouse gasses, which have recently brought the global temperature to within 1 degree Celcius of the maximum temperature the Earth has seen in the last million years.
"This evidence implies that we are getting close to dangerous levels of human-made pollution," Hansen says. "If further global warming reaches 2 or 3 degrees Celcius, we will likely see changes that make Earth a different planet than the one we know. The last time it was that warm was in the middle of the Pliocene, about 3 million years ago, when sea level was estimated to have been about 25 meters (80 feet) higher than today."
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