Trees release their carbon when they die, and they all die relatively quickly on the scales we’re talking about. If harvested and used in long lived construction, it can be longer term, but inevitably it still gets released.
there are extensive chapters written on this topic in IPCC publications, and in the US Climate documents, and in California Climate documents. What you say is partly true, but conveniently omits large other factors at the same time.
Unless the tree gets subducted or interred (aka turned to Coal or similar), it’s still part of the cycle, and its carbon will still eventually return to the atmosphere.
And with the evolution of lignin eating fungi (white rot fungi being particularly efficient) many millions of years ago, good luck with that.
ok, so far.. there appear to be at least two angles.. One is the factual measure of the role of carbon in various forests over time; the second is as a target for collective action.
Deforestation and forest fire are certainly significant sources of carbon emissions. Not all carbon goes into the atmosphere, however. Given current conditions and human practices, acting now to prevent deforestation and catastrophic forest fire are significant in themselves. Forests and managed forests are an important source of food and trade goods for humans worldwide. Mangrove forests are a topic in themselves.
In IPCC_SRCCL_2019/IPCC_SRCCL_05_Chapter-2:
Global models and national GHG inventories use different
methods to estimate anthropogenic CO2 emissions and
removals for the land sector. Consideration of differences in methods can enhance understanding of land sector net emission such as under the Paris Agreement’s global stocktake (medium confidence). Both models and inventories produce estimates that are in close agreement for land-use change involving forest (e.g., deforestation, afforestation), and differ for managed forest. ...
The gross emissions from AFOLU (one-third of total global emissions) are more indicative of mitigation potential
of reduced deforestation than the global net emissions
(13% of total global emissions), which include compensating deforestation and afforestation fluxes (high confidence). The net flux of CO2 from AFOLU is composed of two opposing gross fluxes:
(i) gross emissions (20 GtCO2 yr–1) from deforestation, cultivation of soils and oxidation of wood products, and (ii) gross removals (–14 GtCO2 yr–1), largely from forest growth following wood harvest and agricultural abandonment (medium confidence). {2.3.1}
Land is a net source of CH4 ... emissions for the 2006–2017 period (medium confidence). The pause in the rise of atmospheric CH4 concentrations between 2000 and 2006 and the subsequent renewed increase appear to be partially associated with land use and land use change. The recent depletion trend of the 13C isotope in the atmosphere indicates that higher biogenic sources explain part of the current CH4 increase and that biogenic sources make up a larger proportion of the source mix than they did before 2000 (high confidence).
--
"Terrestrial greenhouse gas fluxes on unmanaged
and managed lands Agriculture, forestry and other land use (AFOLU) is a significant net source of GHG emissions (high confidence), contributing to about 23% of anthropogenic emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) combined as CO2 equivalents in 2007–2016 (medium confidence). AFOLU results in both emissions and removals of CO2, CH4 and N2O to and from the atmosphere (high confidence). These fluxes are affected simultaneously by natural and human drivers, making it difficult to separate natural from anthropogenic fluxes (very high confidence). {2.3} The total net land-atmosphere flux of CO2 on both managed and unmanaged lands very likely provided a global net removal from 2007 to 2016 according to models (-6.0 ± 3.7 GtCO2 yr–1)"
None of that contradicts what I’m saying on any meaningful timescales. You’re literally quoting 1-2 decades. That is short term.
And frankly, it’s obvious. Carbon in any form takes up space. If a forest continually sequestered carbon in solid form (in excess of its wood content, which is easy to measure and plateaus VERY quickly!), every forest that was more than a couple decades old would be sitting on top of a layer of carbon hundreds or thousands of feet deep. It would have to be.
Even the healthiest forests are lucky to have a dozen feet of soil with meaningful carbon content, and most of them it’s a couple feet.
There is nowhere else for that carbon to go except the atmosphere.
And eventually - in hundred, or a few cases a thousand or so years - all those trees die due to climate changes or fires, and they’re gone. Back into the atmosphere.
Think carbon capacitor, not carbon sink.