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How much can forests and gardens really help avoid climate catastrophe

David Klein


Dan wrote on the organizing listserve: "Relevant to this discussion, in the New Left Review, Troy Vettese recently proposed democratic mass reforestation in order to create a "bloodless second Little Ice Age." If we gave up about a fifth of our meat consumption (as doctors and ecologists are recommending anyway) and reforested the considerable freed up land, the effect would be to "decrease atmospheric carbon pollution at the scale of 85 ppm, bringing it to a much safer range in the low 300s ppm." Vettese calls this "natural geoengineering." I hate the name but love the concept. Even if he's overstating the benefits somewhat, it's still very promising. Unlike the first Little Ice Age, it's compatible with respecting indigenous sovereignty and freedom."
Troy Vettese: To Freeze the Thames. New Left Review 111, May-June 2018.

Black Rose Anarchist Federation promotes this plan as part of their proposal for "Avoiding Hothouse Earth." Richard, I'd be curious to know your thoughts on it. It actually draws in part on your own work.
Avoiding “Hothouse Earth”: Organizing Against Climate Catastrophe and Extinction

This is fantasy. Lowering atmospheric concentration by 85 ppm by planting gradens and forests alone is just pie-in-the-sky. To lower atmospheric concentration of carbon by 85 ppm means pulling out 180.2 billion metric tons of carbon (which means drawing down 660.8 billion metric tons of CO2). For a realistic assessment see Hansen et al 2017 paper which explains:

"Smith (2016) estimates that soil carbon sequestration has potential to store 0.7 PgC yr−1. However, as with carbon storage in forest, there is a saturation effect. A commonly used 20-year saturation time (IPCC, 2006) would yield 14 PgC soil carbon storage, while an optimistic 50-year saturation time would yield 35 PgC. Use of biochar to improve soil fertility provides additional carbon storage of up to 0.7–1.8 PgC yr−1 (Woolf et al., 2010; Smith, 2016). Larger industrial-scale biochar carbon storage is conceivable, but belongs in the category of intensive negative emission technologies, discussed below, whose environmental impacts and costs require scrutiny. We conclude that 100 PgC is an appropriate ambitious estimate for potential carbon extraction via a concerted global-scale effort to improve agricultural and forestry practices with carbon drawdown as a prime objective."​

For those not familiar with the units, 1 petrogram of carbon (PgC) is the same as 1 billion metric tons of carbon (a metric ton is about 2200 pounds, so 10% larger than 1 ton in US standard units). Hansen et al estimate a maximum practical carbon sequestration capacity of the world's soils and biomass of 100 billion metric tons.

In the same paper Hansen et al wrote (referring to an earlier paper), "Hansen et al. (2013a) suggested a goal of 100 PgC extraction in the 21st century, which would be almost as large as estimated net emissions from historic deforestation and land use (Ciais et al., 2013)." [bold added]

In other words, the net CO2 emission from historic deforestation and land use is about 100 billion tons of carbon. The number above,180 GtC from the IPCC, which Black Rose Anarchist Federation seems to have glommed onto does not take into account historical CO2 uptake from the land. To pile oversight on top of overestimation, one needs to be aware that carbon extraction from the atmosphere causes the oceans to release the carbon it holds back into the atmosphere. So even if in some sort of science fiction scenario, we could plant enough trees to bring down atmospheric concentrations by 85 ppm, the oceans would try to achieve equilibrium by releasing large amounts of carbon back into the atmosphere.

How much carbon drawdown is actually needed to stay within 1.5C? From the same paper,

"CO2 extraction required to achieve 350 ppm CO2 in 2100 was ~ 100 PgC if 6 % yr^-1emission reductions began in 2013 (Hansen et al., 2013a). Required extraction is at least ~ 150 PgC in our updated scenarios, which incorporate growth of emissions in the past 4 years and assume that emissions will continue at approximately current levels until a global program of emission reductions begins in 4 years."
Ultimately the topic of carbon extraction and storage needs to be on the table for any post capitalist era, and possibly before.


David J

I'm trying to understand this concept of "equilibrium" ie, the oceans putting back what is removed from the atmosphere. Is there a specific rate at which the oceans release stored CO2? What ppm represents equilibrium? And would promotion of kelp beds and other surface aquatic plants be the better option?

David Klein

Quoting from: Geoengineering Strategy Increasing the Emissivity of the Atmosphere by Direct GHG Capture - Power Generation

"Basic thermodynamics predicts, and geochemical models have shown, that removal of atmospheric CO2 by a terrestrial sink, such as tree farming or chemical weathering, will result in the out-gassing of CO2 from the oceans [42]. Assuming humanity ultimately succeeds in eliminating its carbon emissions, the global oceans will require centuries to off-gas the excess dissolved CO2 before the ocean-atmospheric system begins to approach thermodynamic equilibrium [1] ."
In answer to one of your questions, kelp beds and other aquatic plants could store carbon, but when they are eaten or die they release the carbon back to the ocean or atmosphere. In answer to another question, equilibrium can exist in principle at virtually any concentration (in ppm) in the atmosphere as long as there is an appropriate corresponding concentration in the oceans. In more detail, the carbon flux between ocean and atmosphere depends on many factors and is complicated. You can learn probably more than you ever wanted to know here:

Quantifying the drivers of ocean‐atmosphere CO2 fluxes