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Article  Original sin + Plants might absorb more CO2 from human activities than expected

C C Offline
Original sin: Belief that climate science can make politics lead to desired policy

INTRO: Over the past few days I have commented on X/Twitter about the just-released Fifth U.S. National Climate Assessment (NCA). It is much more a glossy promotional brochure than anything resembling a careful assessment of the scientific literature on climate change and the United States. That’s a shame because scientific assessments are crucially important. Instead, the U.S. NCA pours fuel on the pathological politicization of climate science... (MORE - details)

New research suggests plants might be able to absorb more CO2 from human activities than previously expected

INTRO: New research published today in leading international journal Science Advances paints an uncharacteristically upbeat picture for the planet. This is because more realistic ecological modelling suggests the world’s plants may be able to take up more atmospheric CO2 from human activities than previously predicted.

Despite this headline finding, the environmental scientists behind the research are quick to underline that this should in no way be taken to mean the world’s governments can take their foot off the brake[1] in their obligations to reduce carbon emissions as fast as possible. Simply planting more trees and protecting existing vegetation is not a golden-bullet solution but the research does underline the multiple benefits to conserving such vegetation.

“Plants take up a substantial amount of carbon dioxide (CO2) every year, thereby slowing down the detrimental effects of climate change, but the extent to which they will continue this CO2 uptake into the future has been uncertain,” explains Dr Jürgen Knauer, who headed the research team led by the Hawkesbury Institute for the Environment at Western Sydney University.

“What we found is that a well-established climate model that is used to feed into global climate predictions made by the likes of the IPCC predicts stronger and sustained carbon uptake until the end of the 21st century when it accounts for the impact of some critical physiological processes that govern how plants conduct photosynthesis.

“We accounted for aspects like how efficiently carbon dioxide can move through the interior of the leaf, how plants adjust to changes in temperatures, and how plants most economically distribute nutrients in their canopy. These are three really important mechanisms that affect a plant’s ability to ‘fix’ carbon, yet they are commonly ignored in most global models” said Dr Knauer... (MORE - details, no ads)

- - - footnote - - -

[1] I.e., keep basing policies on the most extreme, pessimistic models. Maintain the apocalyptic scenario.
confused2 Offline
Quote:plants might be able to absorb more CO2
Everybody loves a good simulation.
Quote:We used the RCP8.5 climate scenario to conduct factorial model simulations characterizing the individual and combined effects of the three mechanisms on projections of GPP. Simulated global GPP increased more strongly (up to 20% by 2070–2099)
More details -
C C Offline
RCP2.6 was used in some instances as well [see footnote 1]. Again, it's not surprising that RCP8.5 was the dominant choice addressed overall since it is the most extreme expectation and thereby usually preferred pathway even for simulations extending beyond mid-century.

RCP8.5: In RCP 8.5, emissions continue to rise throughout the 21st century. Since AR5 this has been thought to be very unlikely, but still possible as feedbacks are not well understood. RCP8.5, generally taken as the basis for worst-case climate change scenarios, was based on what proved to be overestimation of projected coal outputs. It is still used for predicting mid-century (and earlier) emissions based on current and stated policies.

RCP8.5 tracks cumulative CO2 emissions: Despite some recent progress on bending the emissions curve, RCP8.5, the most aggressive scenario in assumed fossil fuel use for global climate models, will continue to serve as a useful tool for quantifying physical climate risk, especially over near- to midterm policy-relevant time horizons. Not only are the emissions consistent with RCP8.5 in close agreement with historical total cumulative CO2 emissions (within 1%), but RCP8.5 is also the best match out to midcentury under current and stated policies with still highly plausible levels of CO2 emissions in 2100.

The reference to "more realistic ecological modelling" was probably referring to updated, more accurate models of photosynthesis rather than "more plausible" climate models and projections.

EXCERPT (OP paper): However, such model deficiencies may compromise the predictive capability of these models when confronted with new conditions as imposed by climate change, an issue that is likely alleviated by more realistic representations of photosynthesis that mirror our latest understanding of plant physiological functioning.

- - - footnote - - -

[1] RCP2.6 excerpts: [...] We conducted global factorial simulations forced by historical (1900–2005) and projected climate (2006–2099) using the RCP2.6 and RCP8.5 climate scenarios.

[...] An additional set of simulations with the more moderate RCP2.6 climate scenario showed much lower increases in GPP in the first half of the 21st century and a decline thereafter (fig. S2). Despite these contrasting trajectories, differences across experiments were qualitatively similar to those in the RCP8.5 scenario. All results hereafter refer to the RCP8.5 scenario, unless stated otherwise.

[...] For the main simulations, we selected the RCP8.5 scenario which represents a very high emission pathway. Additional simulations were performed using the RCP2.6 scenario, which is consistent with the temperature target of the Paris Agreement...
confused2 Offline
The simulation in the OP assumes (IMHO) CO2 is the main factor limiting 'plant' (tree?) growth. Some real experimental work (not simulations) carried out on natural ecosystems (forests) suggests ".. that the effect significantly diminished over time due to a nitrogen limitation.". While the nitrogen limitation can be fixed for cultivated crops I'm not sure (any evidence?) what would happen in the remaining biomass of the planet.


Quote:Scientists have observed the CO2 fertilization effect in natural ecosystems, including in a series of trials conducted over the past couple decades in outdoor forest plots. In those experiments artificially doubling CO2 from pre-industrial levels increased trees’ productivity by around 23 percent, according to Norby, who was involved in the trials. For one of the experiments, however, that effect significantly diminished over time due to a nitrogen limitation. That suggests “we cannot assume the CO2 fertilization effect will persist indefinitely,” Norby says.

Politics have elevated the paper far beyond its real value.
More work is needed.
C C Offline
(Nov 20, 2023 12:04 AM)confused2 Wrote: Politics have elevated the paper far beyond its real value.
More work is needed.

Hopefully it's not receiving that kind of spotlight, especially since the authors went out of their way to suggest it is unimportant (for policy). I believe that's an informal moral expectation in climate science now, for researchers to apologize either in advance or along the content of the paper for anything that might be construed or misconstrued as even mildly positive.

Perhaps, however, that does add a new perspective on the proposal of experts last year who urged climate scientists to stop doing research, as a form of protest. Instead, only have researchers noted for adding remorseful prefaces or repentant postscripts to their work engage in a moratorium. Since there would be nothing lost there in terms of bolstering the narrative.

Should Climate Scientists Stop Doing Research? These Experts Say Yes

"...We call for a moratorium on climate change research until governments are willing to fulfill their responsibilities in good faith and urgently mobilize coordinated action from the local to global levels.”

[ response...] “Nothing says fixing the science-social contract like stopping people’s careers and knowledge production, and waiting for action from other people,” he said. “That will show ‘em.”


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