(Image source: NOAA)
According to reports from the Mauna Loa Observatory, worldwide CO2 averages for last week were 397.92 ppm. Daily measurements showed CO2 levels exceeding 398 ppm. And it appears likely that monthly CO2 averages for March will be in the range of 397.5 ppm. At this pace, it appears that worldwide CO2 will come very close to touching 400 ppm averages in May of this year and will certainly exceed the 400 ppm threshold by 2014.
Scientists have set the safe limit for worldwide CO2 levels at 350 ppm. We are currently far in excess of that number.
The last time CO2 was 400 ppm was between 2-3 million years ago. So a sustained CO2 of this level over long periods would continue to drive radical environmental changes. A world with average CO2 of 400 ppm, according to paleoclimate, eventually becomes 2-3 degrees hotter than today. Sea levels in such a world rise, over time, and eventually stabilize between 15 and 75 feet higher than today.
The average pace of CO2 increase over the past ten years is more than 2 ppm each year. This pace of increase is many times faster than any period in the geological record. At 400 ppm, worldwide CO2 will be about 125 ppm higher than in 1880. During the ice age, worldwide CO2 averaged around 190 ppm. The jump from 190 ppm to 275 ppm set off changes in Earth’s heat balance that increased global temperatures by more than 5 degrees Celsius, melted the great Laurentide ice sheet, and caused sea levels to rise by scores of feet.
Under business as usual fossil fuel burning, scientists expect world CO2 levels to reach between 600 and 850 ppm by the end of this century. Such high levels of CO2 have not been seen for 6 million years or more. Further, the massive forcing a jump to 600 to 850 ppm would induce would likely result in feedbacks that continue to push worldwide greenhouse gasses even higher. Many scientists believe that this would result in enough heat increases to make the world very hostile to life.