--> Can Soils Solve Climate Change? – Jesse Reynolds / international & technology environmental policy

Another dubious claim of natural climate solutions makes the rounds

Originally published at Legal Planet

A few months ago, I questioned a claim that planting trees could solve climate change. According to some scientists, reforestation “is by far the cheapest solution that has ever been proposed,” and for $300 billion it could sequester 200 gigatons of carbon (GtC, or 733 GtCO2). Many media outlets swooned, but the assertions were weak if not incorrect. Indeed, just this week, Science — the original outlet — published four scathing critiques of the underlying scientific paper. (See the update at the bottom of my original blog post for more details.)

Last week, a headline from Bloomberg boldly announced “How to Halt Global Warming for $300 Billion,” telling us that “UN scientists say reclaiming wasteland… would stall emissions growth for up to 20 years.” Specifically, the idea is

to lock millions of tons of carbon back into an overlooked and over-exploited resource: the soil…. Returning [900 million hectares of degraded land that could be restored] to pasture, food crops or trees would convert enough carbon into biomass to stabilize emissions of CO2, the biggest greenhouse gas, for 15-20 years… “With political will and investment of about $300 billion, it is doable.”

This struck me as too good to be true. So let’s break down these numbers and compare them with current leading evidence.

Assuming that “to stabilize emissions” means withdrawing enough carbon to compensate for all of our annual greenhouse gas emissions, “15-20 years” implies 200 to 275 GtC, for an average price of $1.10 to $1.50 per ton of carbon (tC, as “giga” = one billion) or $0.30 to $0.40 per GtCO2 (the common way that costs of reducing emissions are reported). This also implies 220 to 300 tC sequestered per hectare of restored land.

Carbon-rich soil, in eastern Pennsylvania, from Flickr user soilscience
Carbon-rich soil, in eastern Pennsylvania, from Flickr user soilscience

Yet soils have lost only 133 GtC  in the course of human history. In terms of cost, a recent review of the scientific literature estimated that spending $20 per GtCO2 could allow the capture of 0.4 GtC (1.38 GtCO2) per year and spending $100 per GtCO2 could allow the capture of 1 GtC (3.7 GtCO2) per year. In other words, the amount of carbon that the Bloomberg article claims could be captured would cost roughly 50 to 300 times as much as reported and would take roughly 200 to 700 years.

Perhaps despite the headline, but implied in the quote, the article means sequestration in all biomass: soil, plants, animals, fungi, etc. Even then, the loss of all biomass in the course of human history has been 379 GtC. Given that the planet has 13 billion hectares of land, the Bloomberg article implies that more than half of all carbon loss from biomass ever could be sequestered by restoring 7% of the world’s land.

The article did not link to any paper or report, and I found no papers or reports on the websites of the international organizations to which it referred. It appears to base its estimates of both the amount of carbon (i.e., 15 to 20 years worth) and the cost on a single quote from Rene Castro Salazar, an assistant director general at the UN Food and Agriculture Organization.*

If it sounds too good to be true, it probably is.

*Update (evening 28 October): One of the authors of the Bloomberg article confirms, “The $300B figure came out of the UNCCD conference in Delhi, from interviews with delegates, including  Castro-Salazar at the FAO.”


1 2 3 7
November 12th, 2021

Moving Solar Geoengineering Research Forward

Three essays in Science aim to take concerns seriously and constructively Solar geoengineering research is not dormant, but it has […]

November 3rd, 2021

Two kinds of international law

Minimal corporate tax rates and environment-as-a-human-right have something in common, other things not. Two developments last month demonstrate the breadth […]

October 26th, 2021

A Proposal to Link Solar Geoengineering and Mitigation

Solar geoengineering–long feared to undermine emissions cuts–may be able to enhance them The leading concern about solar geoengineering–proposed technologies to […]

August 24th, 2021

What If Someone Just Does It?

A scenario exercise on unauthorized use of solar geoengineering This post is co-authored with Edward A. Parson, and also published […]

July 13th, 2021

Earth System Interventions for Sustainability

We actively shape major Earth systems, with increasingly powerful technologies. We should face up to it. Also published at Legal […]

June 4th, 2021

Another Historic Climate Court Ruling in the Netherlands

A court orders Shell to cut its emissions, including of its consumers. But will this stand after appeal? Originally posted […]

May 5th, 2021

Genetically Modifying Wild Species: Could We? Should We?

Originally published in Trends (the electronic newsletter of the Section of Environment, Energy, and Resources of the American Bar Association) […]

April 22nd, 2021

Offering “Carrots” to Protect the Amazon

Brazil asks for a billion dollars to slow deforestation. Would this be cooperation or extortion? Originally posted at Legal Planet. […]

April 6th, 2021

The US National Academies on Solar Geoengineering Research and Governance

Originally published at Legal Planet as “Four Emmett Institute scholars react to an important new report“ The US National Academies […]

March 16th, 2021

“NIABYs” Obstruct Important Climate Change Research

Some activists say “not in my backyard,” but strident opponents of solar geoengineering argue “not in anyone’s backyard.” Originally posted […]