Atmospheric CO2 Nudging Levels Not Seen In 3 Million Years - LiveScience
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There will be no huge atmospheric or climatic shift once carbon dioxide hits 400 ppm, but the milestone has symbolic significance, said Michael Mann, a climate scientist at Pennsylvania State University. "It is a reminder of just how uncontrolled this dangerous experiment we're playing with the planet really is," Mann told LiveScience.
In the 1,000 years that occurred before the Industrial Revolution of the 18th century, atmospheric carbon dioxide held steady at around 270 to 280 parts per million. Scientists believe that the most recent period to reach 400 ppm was the Pliocene Epoch, between 5 million and 3 million years ago, according to the Scripps Institution of Oceanography, which keeps track of the Keeling Curve.
Back then, it was a different world. Global average temperatures during the period were between 5.4 and 7.2 degrees Fahrenheit (3 to 4 degrees Celsius) higher than today, and sea level was as much as 131 feet (40 meters) higher in some places. Even the least-affected regions saw sea levels 16 feet (5 meters) higher than today's.
A major difference between then and now, though, is the speed at which carbon dioxide is rising today. Typically, in the last 40 to 50 years, the Keeling Curve shows increases of 2 to 2.5 ppm a year, Mann said. In the 1950s and 1960s, carbon dioxide increased by less than 1 ppm each year, according to Scripps.
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http://news.yahoo.com/greenhouse-gas-reach-3-million-high-183419959.html
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