Post by Webster Groves on Jul 4, 2014 6:15:16 GMT -6
And while the 400 ppm mark is somewhat symbolic (as the increase in warming between 399 ppm and 400 ppm is small), it serves to show how much carbon dioxide has been put into the atmosphere since preindustrial times, when concentrations were around 280 ppm. The increase in this and other greenhouse gases in the atmosphere has warmed Earth’s average temperature by 1.6°F since the beginning of the 20th century. World leaders agreed at a UN summit in 2009 to limit warming to 3.6°F, but prominent climate scientists like James Hansen have said that amount of warming will still be too much.
The levels of CO2 in the atmosphere vary not only through humanity’s addition of the gas through industrial processes, but also with the biological cycle. Concentrations begin their rise in the winter, when plants are dormant, and continue rising through spring. They reach their peak in May and then begin to decline because plants are in full bloom and are pulling CO2 from the atmosphere to fuel photosynthesis.
But plants only pull so much CO2 out of the atmosphere in a given growing season. Each year they leave a growing excess of about 2 ppm behind, which is why the 400 ppm mark came earlier this year than last and will come earlier still next year.
Annual increases are now regularly breaching the 2 ppm mark, even in a neutral ENSO regime. Only a Nina or volcano event can prevent yearly 2+ppm increases now. Another 10-15 years and we'll be flirting with 3ppm/yr at this rate. I would expect the Amazon to start belching CO2 on a more frequent basis by then (as droughts continue to increase in that region) and research strongly suggests land areas in the Arctic will flip from carbon sink to carbon source in that time and start contributing 0.2-0.6 Gt of carbon per year by the end of that period.
If we haven't seriously started peaking by then, the problem will begin the process of seriously running away from us. We'll then be stuck trying to cut emissions just to offset the increases coming off land biomes.
Welcome to the shout box. Just trying this feature out.
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