I was reading this article today, and I saw this chart of atmospheric carbon dioxide levels for the past year:

Carbon dioxide May 2016-April 2017

The chart shows a decline in atmospheric carbon dioxide levels from roughly June-October, a cycle that appears to be consistent across many years: Longer term atmospheric carbon dioxide

Why does this cycle occur? It looks like the period of decline coincides with the season of greatest plant growth in the northern hemisphere. Or is it that energy demand rises so much during the northern-hemisphere winter that the CO2 levels for the entire atmosphere are quickly changed?

  • $\begingroup$ I've heard this explained by the Amazon rain forest, sometimes called the "lungs of the planet". english.cntv.cn/program/china24/20130411/106725.shtml But I don't know if that's truly the reason, or if it's a combination of factors, perhaps ocean absorption/plankton growth could be a significant factor. $\endgroup$
    – userLTK
    Commented Apr 21, 2017 at 5:44
  • $\begingroup$ It may depend on where it is measured in the atmosphere. If they measure it at a same height it will differ according to season because the height of troposphere/atmosphere itself changes due to differences in pressure. This in turn leads to differences in transportation of CO2. $\endgroup$ Commented Aug 15, 2017 at 8:55


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