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Only half of anthropogenic CO2 emissions remain in the atmosphere. This is easy to check by comparing the rate of emissions against the rate of increase in atmospheric CO2. I have read from various sources that the remainder is absorbed - roughly in equal proportions - by two sinks, namely the ocean and the biosphere (some sources just say "woodland"). However, the total area of woodland globally has been shrinking for many decades. My question is: how can woodland be a carbon sink when it is shrinking?

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  • $\begingroup$ First of all, it is difficult to answer without having sources to base your question on. However, we need to look at the process. This means that as biotopes decline, an important sink for atmospheric CO2 disappears. Thus, there should be a positive correlation between the increase in atmospheric CO2 and declining biotopes. $\endgroup$
    – Weiss
    Jun 14, 2023 at 8:59
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    $\begingroup$ can you give us the Sources? So it is important to distinguish between the sort time and longe time CO2 cycle $\endgroup$
    – Weiss
    Jun 14, 2023 at 13:06

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I agree that this kind of source and sink budgeting is a little bit misleading. The answer to your question is that the land use change you mentioned to be a source of CO2 is added to the anthropogenic CO2 emissions. And indeed it is about as large as the sink effect of the biosphere (check out the figure I found in a WMO article).

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  • $\begingroup$ That is interesting as it suggests that we only need to double the total deforested area to completely negate this sink. It also suggests that the area that was not deforested has changed behaviour in response to increased atmospheric carbon. My question is, how? Where is it putting all that carbon? $\endgroup$ Jun 14, 2023 at 9:11
  • $\begingroup$ I think that does answer half the question. Essentially the shrinkage is accounted as an emission. The other half is, why is the remaining forest not net-zero? $\endgroup$ Jun 14, 2023 at 9:22
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    $\begingroup$ Because the Biosphere is naturally sequestering carbon through deposition of organic material into the soil (mainly). And yes, due to increase in atmospheric CO2, the biosphere's carbon uptake has also increased (CO2 Fertilization Effect). Check out this wikipedia article. $\endgroup$
    – hschoell
    Jun 14, 2023 at 15:05

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