Consider the graph below compiled by NASA, illustrating how CO2 levels have risen from 280 ppm to 380 ppm in just the last 60 years. CO2 levels are now significantly higher than they've been in the last 650,000 years.
Over the past three decades, scientists have reconstructed the composition of the earth's atmosphere for the past 650,000 years by drilling deep into the Greenland and Antarctic ice sheets, as much as 2 miles into those ice sheets to extract core ice samples which are full of air pockets that represent time capsules of the earth's atmosphere.
In fact, scientists estimate the last time CO2 levels were this high was during the Middle Miocene -- approx. 15 million years ago. The earth was a dramatically different place then. Mean global temperatures were 5-10 degrees warmer, there were no polar ice caps and sea levels were 75-120 ft. higher.
http://climate.nasa.gov/evidence/
Over the past three decades, scientists have reconstructed the composition of the earth's atmosphere for the past 650,000 years by drilling deep into the Greenland and Antarctic ice sheets, as much as 2 miles into those ice sheets to extract core ice samples which are full of air pockets that represent time capsules of the earth's atmosphere.
In fact, scientists estimate the last time CO2 levels were this high was during the Middle Miocene -- approx. 15 million years ago. The earth was a dramatically different place then. Mean global temperatures were 5-10 degrees warmer, there were no polar ice caps and sea levels were 75-120 ft. higher.
http://climate.nasa.gov/evidence/
