Limited climate change mitigation potential through forestation of the vast dryland regions

[Andrew Lockley]

https://www.science.org/doi/10.1126/science.abm9684

Forestation of the vast global drylands has been considered a promising climate change mitigation strategy. However, its actual climatic benefits are uncertain because the forests’ reduced albedo can produce large warming effects. Using high-resolution spatial analysis of global drylands, we found 448 million hectares suitable for afforestation. This area’s carbon sequestration potential until 2100 is 32.3 billion tons of carbon (Gt C), but 22.6 Gt C of that is required to balance albedo effects. The net carbon equivalent would offset ~1% of projected medium-emissions and business-as-usual scenarios over the same period. Focusing forestation only on areas with net cooling effects would use half the area and double the emissions offset. Although such smart forestation is clearly important, its limited climatic benefits reinforce the need to reduce emissions rapidly. 

[Albert Bates]

I found this article quite hopeful actually. There have been a lot of unsupported reactions to the afforestation of drylands. This study finds that after subtracting the albedo effect, reforestation/afforestation has a nearly 30% net cooling effect. I actually think that the 448 MHa estimate (approx nine Spains) is low once in-fill regrowth is fully quantified, not just the broadscale open regions surveyed by satellite. BAU Scenarios are a bit of a red herring because they follow an impossible exponential trend. I often hear that "deserts have their own ecology" and need to be protected, and while that is true to a degree, it is also true that many, if not most, are recent and anthropogenic. Putting back forests where they once were is one means we have to restore balance to the carbon cycle at a planetary scale.

[Suzanne Reed]

I appreciated the targeting approach but issues of water supply, tree species, and species mix are relevant to this topic, especially when there is intent to rely on reforestation and sequestration as offsets.

Suzanne

Suzanne Reed

Healthy Planet Action Coalition

https://www.healthyplanetaction.org/

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Suzanne

Suzanne Reed

The Collaboration Connection

https://www.collaborationconnection.org/

[Michael Hayes]

Thanks for the clarity, Suzanne. Biology is never simplistic, the Sahara was likely green not that long ago.

I follow marine carbon issues in general and the oceanic deserts in particular. To support terrestrial soil-based solutions, at a multi-gigaton/yr scale, one obviously has to look at the soil water/energy/nutrient nexus needs at the equivalent scale. I support using the oceanic desert-based WENN resources for vast scale soil improvements as that overall land/sea strategy works the planetary C cycle at two important extreams and in a mutually supportive STEM, policy, and economic fashion.

https://www.nature.com/articles/news.2008.795#:~:text=Low%2Doxygen%20regions%20have%20expanded,years%2C%20according%20to%20new%20measurements.

We have an excess of marine C yet a shortage of soil C. The same can be said for nutrients and marine deserts are likely expanding far faster than terrestrial deserts. Farming the oceanic deserts for WENN resources, that can be applied to vast scale terrestrial efforts, would likely help mitigate marine desert expansion to some extent simply by operating in those waters. We need to cool vasts amounts of seawater, adjust the pH of a vast amount of seawater along with other measures, and as you likely know, with minimal impact on wildlife. 

Marine Cloud Brightening, artificial upwelling, biomass cultivation, electrolysis, fresh water/ice production etc would be technically supportable while providing upstream WENN resources for vast scale terrestrial efforts. The above does represent a rather complex biotic and abiotic STEM basket, policy and economic basket yet the full spectrum of the critical STEM components is likely available today. Policy and economics of such a vast scale shifting of resources are, as we all recognize, different chapters.

Best regards 

Michael Hayes 

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[Suzanne Reed]

Complex indeed, Michael!  Thank you for responding to my comments and expanding the scope of the conversation to a more holistic framework.  Humans have done a right good job of disrupting all ecosystem cycles and relationships and the economies that depend on them.  Many of our Healthy Planet Action Coalition participants are exploring various aspects of direct climate cooling and GHGR to contribute to ecosystem restoration.  You may be interested in the Compilation of Comments on the White House Office of Science and Technology Programs-lead study of climate intervention research needs found here,  https://docs.google.com/document/d/1v2eoFQUtXc7J3vX37jJ2dBAJUiBPRNMu/edit?usp=sharing&ouid=117772987047166624642&rtpof=true&sd=true

The work of The Climate Foundation may be of particular interest if you are not already familiar with it.

Best wishes,

Suzanne

[Michael Hayes]

Thanks, Suzanne

The struggle with future-proofing such large investments and policy decisions is likely the primary limiting factor in the WH and industry. Everyone involved wants longterm dependability yet STEM advancements are now in an exponential rate of increase and new STEM, last years breakthroughs, are rapidly being made obsolete.

The WH does likely need an office(r) of CDR STEM, policy, and economics synthesis simply to short through the many concepts to find STEM commonalities that can be exploited to help avoid almost immediate STEM obsolescence. In example, MCB and Ocean Alkalinity Enhancement have technical commonalities, invest in one and that supports the other, microalgae cultivation using floating bioreactors has a technical connection to OAE and OTEC has a technical connection to bioreactors, etc. The more STEM commonalities we find, the better for the investors and politicians as it helps future-proof the investment in the STEM. A web of mutually supportive technology is more reliable than any single tech option.

This CDR group has done an outstanding job, a world class job, at detailing and debating the many different CDR options yet finding STEM commonalities that can be used to future-proof the likely huge investment of political capital as well as capital itself that CDR now needs may best help policy makers and investors drop the hammer.

Best regards

[Andrew Lockley]

From what I understand this study doesn't include cloud fraction changes, so it's pretty limited. Correct me if I'm wrong 

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[Michael Hayes]

Andrew,

The authors do seem to have considered cloud fractions, as in, [...] is also known to cool the local climate by increasing evaporation and inducing increased cloud formation (4, 5). [...]

The surface biology does play a strong roll in the makeup of the local atmospheric biology, and thus cloud formation/thickening, as we find with the ubiquitous and highly talented, and mostly atmospheric, microbe P. syringae.

https://web.mst.edu/~djwesten/MoW/BIO221_2010/P_syringae.html

How this all connects to CDR, however, is largely moot as most forests, especially in today's hot climate, will give up their C rather quickly. As such, the value of this paper to the CDR discussion would seem highly limited.

Regards

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[Bruce Melton -- Austin, Texas]

I want to second Michael's assertion that forests will give up their C quickly. Actually, I want to see his suggestion and raise it to, "Many, if not most forests globally are now net emitters of greenhouse gasses and the trend of increased emissions will likely increase exponentially in the very near future."

Canada's forests are already emitting 250 Mt CO2e annually. The Amazon, at least 1 Gt annually. Permafrost, which is net for the northern ecology, 2.3 Gt. Amazon and Permafrost are averages and current emissions are likely double considering the trend is linear and the trend is very likely not linear. This is 7 Gt CO2e annually from just these studied systems.

In addition: Australian tropical forest mortality has doubled from water stress, halving C storage and flipping to emissions. The authors say they are working on quantification but importantly, the findings say Australian tropical forests are likely analog to southeast Asian tropical forests. When I asked the principal to confirm, he (Bauman) said on hindsight, "what makes the results of a marked increase in background mortality likely generalisable, to some extent, to other moist tropical regions, is the mechanism highlighted (atmospheric evaporative demand is increasing worldwide; the physiology of atmospheric water stress response is the same across tree species irrespective of their region of origin), the similarity of the climatic conditions of the studied region to the mean climate of other tropical moist forests on other continents, and the fact that the mortality increase spans the wide range of
functional traits considered in the study and found elsewhere."

In addition: When I read Bauman 2022, and I realized a doubling of mortality halves carbon storage and flips a forest to emissions, I then re-visited McDowell 2015's western North American forest mortality findings. With McDowell's summarization of other findings of a near doubling to quadrupling of mortality, mostly greater than a doubling, one can interpret that western North American forests have flipped to emissions too. Given all of this, and considering what Bauman said about tropical forests globally and water stress, it can be interpreted that most forests globally have now flipped from sequestration to emissions.

MeltOn

(Summaries below from my archives)

Canada's Forests Flip to Carbon Source… Emitting 250 Mt annually, started net emissions in 2002 because of beetle kill. The rate of climate change is 10 to 100 times faster than Canada's forests can adapt. "Scientists predict that increasing temperatures and changes in weather patterns associated with climate change will drastically affect Canada’s forests in the near future. With the rate of projected climate change expected to be 10 to 100 times faster than the ability of forests adapt naturally."  And, "Traditionally, foresters have used local tree seed for planting seedlings, as local populations were generally thought to be best adapted to the climate conditions of the site. However, with a rapidly changing climate, these local populations may not be able to adapt quickly enough, and while well-established adult trees can often withstand increased stress, seedlings are highly vulnerable."
Seamus O’Regan, Minister of Natural Resources, Introductory Letter.
The State of Canadas Forests, Canadas Forests, Adapting to Change, Canadian Forest Service, 2020.
https://d1ied5g1xfgpx8.cloudfront.net/pdfs/40219.pdf

Qin 2021 - Amazon emissions of 0.67 Pg C (2.45 Gt CO2eq) from 2010 to 2019 based on satellite canopy density, with forest degradation 3X the loss of deforestation… "During 2010-2019, the Brazilian Amazon had a cumulative gross loss of 4.45 Pg C against a gross gain of 3.78 Pg C, resulting in net AGB loss of 0.67 Pg C. Forest  degradation (73%) contributed three times more to the gross AGB loss than deforestation (27%), given that the areal extent of degradation exceeds deforestation. This indicates that forest degradation has become the largest process driving carbon loss and should be come a higher policy priority."
Qin et al., Carbon loss from forest degradation exceeds that from deforestation in the Brazilian Amazon, Nature Climate Change, April 29, 2021.
preprint - https://www.researchgate.net/publication/361323731_Carbon_loss_from_forest_degradation_exceeds_that_from_deforestation_in_the_Brazilian_Amazon
Paywall - https://www.nature.com/articles/s41558-021-01026-5

Gatti 2021 - Amazon emitting, not absorbing, 1 Gt CO2 annually on average from 2010 to 2018… "The study found fires produced about 1.5bn tonnes of CO2 a year, with forest growth removing 0.5bn tonnes. The 1bn tonnes left in the atmosphere is equivalent to the annual emissions of Japan."
Carrington, Amazon rainforest now emitting more CO2 than it absorbs, Guardian, July 14, 2021.
https://www.theguardian.com/environment/2021/jul/14/amazon-rainforest-now-emitting-more-co2-than-it-absorbs
Gatti et al., Amazonia as a carbon source linked to deforestation and climate change, Nature, July 14, 2021.
https://www.nature.com/articles/s41586-021-03629-6.epdf?sharing_token=lsfPlVRsW05dUMB_VD-zItRgN0jAjWel9jnR3ZoTv0NILaci0q8CXtVe4JKM-xF0Z0ZQpmJpnpSclAjJeIV-vCjviXK_Mb9hvvU5C3CiJVgu82-RGuHR01gFiQZAVMzDCCxiRyvlh0MBQxTvGN2oHmf2jIOC7MEEGXrOPGIblsh57v9qXkkZbM7U0OH8zbdQ4jnVO1zD9R1jeDcUVBS22YVLkjWEvC5vrNMdQ416fmEBL9kIHYs2ptVibFKXLxEuh-TQ08w-QGSFzN6221KgguYTe0Q9FoZ1J-Wksf4tWXrjv-xu34UpgYqxQWwLTTbTgHYTuglT_tSVd4WaweL9fg%3D%3D&tracking_referrer=www.theguardian.com

Natali 2019 - Permafrost Collapse is Underway With Emission Plausibly Rivaling All of Global Transportation... "Here we synthesize regional in situ observations of CO2 flux from Arctic and boreal soils to assess current and future winter carbon losses from the northern permafrost domain. Across the Northern Hemisphere, permafrost melt emitted 630 TgC, or 2.3 Gt CO2eq. "We estimate a contemporary loss of 1,662 TgC per year from the permafrost region during the winter season (October–April). This loss is greater than the average growing season carbon uptake for this region estimated from process models (−1,032 TgC per year)." Of critical note, emission are average per year from 2003 – 2017. With permafrost melt increasing rapidly today, this means emission in 2017 were much more than in 2003, therefore emissions today are much more than the 2.3 Gt per year estimated on average, quite likely double the 2.3 Gt and possibly triple or quadruple and rivalling global transportation CO2 emissions for about 6.7 Gt CO2  per year... "The dataset represents more than 100 high-latitude sites and comprises more than 1,000 aggregated monthly fluxes. We examined patterns and processes driving winter CO2 emissions and scaled fluxes to the permafrost domain using a boosted regression tree (BRT) machine learning model based on hypothesized drivers of winter CO2 flux. Environmental and ecological drivers (for example, vegetation type and productivity, soil moisture and soil temperature) obtained from satellite remote sensing and reanalysis data were used to estimate regional winter CO2 emissions for contemporary (2003–2017) climatic conditions."
Natali et al., Large loss of CO2 in winter observed across the northern permafrost region, Nature Climate Change, October 21, 2019.
https://www.uarctic.org/media/1600119/natali_et_al_2019_nature_climate_change_s41558-019-0592-8.pdf

Bauman 2022 - Australian Tropical Forest Flip from sequestration to emissions… Bauman et al,. analyzed a 49-year record across 24 old-growth tropical forests in Australia and found mortality has doubled across all plots in the last 35 years indicating a halving of life expectancy and carbon residence time. Losses were not offset by gains from growth and regrowth. Thresholds involving atmospheric water stress, driven by global warming, may be a primary cause of increasing tree mortality in moist tropical forests. "Model predictions indicate a doubling in average mortality risk across plots between the 1980s and 2010s, corresponding to a potential halving of tree life expectancy and carbon residence time... Carbon loss from a doubling of tree mortality was not offset by gains, converting these forests into biomass carbon sources."
Bauman et al., state, "Many of the species in our plots are widespread across tropical Southeast Asia, offering a robust assessment of climate niche." A personal communication with Bauman, where I asked if the above statement was one where Australian tropical forest mortality was an analog to Southeast Asian tropical forest mortality, reveals that on hindsight he would have modified this analog with Southeast Asian tropical forests to, "what makes the results of a marked increase in background mortality likely generalizable, to some extent, to other moist tropical regions, is the mechanism highlighted (atmospheric evaporative demand is increasing worldwide); the physiology of atmospheric water stress response is the same across tree species irrespective of their region of origin."
Bauman et al., Tropical tree mortality has increased with rising atmospheric water stress, Nature, May 17, 2022.
(Researchgate, free account required) https://www.researchgate.net/publication/360691427_Tropical_tree_mortality_has_increased_with_rising_atmospheric_water_stress

McDowell 2015 - Forest Mortality in Western North America between 1980 and the mid-2000s with much of the increase happening recently rather than earlier…It is also pertinent that warming since the mid-2000s has just about doubled as of 2022, and that much of the western US forest mortality from bark beetles was not captured in these evaluations.
- Sierra Nevada mortality has about doubled from 0.75 to 1.5 percent
- Western Canada mortality has quadrupled from 0.6 percent to 2.5 percent
- Eastern Canada has nearly doubled from 0.8 to 1.45 percent
- Western US interior forests have more than doubled from 0.3 percent to 0.65 percent.
- Pacific Northwest has tripled from 0.45 to 1.25 percent
McDowell et al., Multi-scale predictions of massive conifer mortality due to chronic temperature rise, Los Alamos National lab, nature Climate Change, December 21, 2015.
https://www.acsu.buffalo.edu/~dsmackay/mackay/pubs/pdfs/nclimate2873.pdf
from :
Peng, S. et al. A drought-induced pervasive increase in tree mortality across
Canada's boreal forest. Nature Clim. Change 1, 467471 (2011).
and, Van Mantgem, P. J. et al. Widespread increase of tree mortality rates in the western United States. Science 323, 521524 (2009).

Bruce Melton PE
Director, Climate Change Now Initiative, 501c3
President, Melton Engineering Services Austin
8103 Kirkham Drive
Austin, Texas 78736
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[Chris Van Arsdale]

(I have not read this closely)

Presumably "dryland regions" don't have a lot of existing C to give up, so the net emitter argument is probably not applicable here.

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[Bruce Melton -- Austin, Texas]

Hola Chris,

Andrew and I were both talking about "most forests." This concept of most forests now being carbon emitters is very new, not well represented in findings yet, and certainly not published enough for the consensus to be onboard. This is an abrupt reaction to climate warming where global ecologies, or Earth systems, are collapsing from water stress and water stress related impacts, most commonly referred to as tipping. See also Badgley et al., California's forest carbon offsets buffer pool is severely undercapitalized, Frontiers in forests and Global Change, August 5, 2022, where wildfire has burned 95 percent of California's carbon pool buffer meant to protect the carbon credit pool from fire and disease mortality for the next 100 years.

On the carbon content of the Great Plains of the US - 7.5 Gt C, (27.5 Gt as CO2) with an enhanced capacity of another 2.5 Gt C (9 Gt as CO2) by 2050, relative to the chosen scenarios by USGS in https://pubs.usgs.gov/pp/1787/p1787.pdf.

This study looks at the carbon efficiency of dryland conversion to forests and finds it poor in general. What the authors do not do is propose how to convert drylands where forests do not grow naturally into forested areas. These drylands are not deserts. It appears the demarcation the authors used between desert and dryland is about 15 inches of precip annually, based on the areas identified as being evaluated in the image below, with consideration for warm season drying potential.

The concept of afforestation of dryland regions however, at least in the Great Plains of North America, is flawed for two reasons.

1) The only place a native species forest is capable of growing in the Great Plains of North America is almost completely the areas immediately along watercourses. Then the predominant species are poplar, which are relatively short lived and fragile. The only way to create native species forests in the Great Plains is with supplemental water of which there is little and great competition for it from food crops. If this irrigation is stopped, afforested areas die.

2) Using non-native tree species tolerant of less water is plausible but causes great degradation or extinction of existing natural systems and is generally irreversible.

This idea of afforestation is good sounding idea, but it is fraught with equity considerations that I have never been able to justify. (Degradation of extinction of natural systems, displacement of food crops and BECCS crops, and disrespect of indigenous people's lands.) If anyone can help me understand the justification for these strategies, please sing out.

Cheers,

B

Bruce Melton PE
Director, Climate Change Now Initiative, 501c3
President, Melton Engineering Services Austin
8103 Kirkham Drive
Austin, Texas 78736
(512)799-7998
ClimateDiscovery.org
ClimateChangePhoto.org
MeltonEngineering.com
Face...@Bruce.Melton.395
Inst...@Bruce.C.Melton
The Band Climate Change
Twitter - BruceCMelton1