This article looks at what is called nature-based carbon dioxide removal.
While tree planting has long been a substantial nature-based part of the climate pollution challenge, increasingly we are finding that both existing and future warming are creating a reality where these long-held forest truths are no longer valid. Not only has current warming reduced the viability of forests to store carbon, future warming on our way to the widely held best-case warming scenario of 1.5 C will further reduce forests’ ability to store carbon.
A recent academic publication suggests planting (about a trillion) trees “remains among the most effective strategies for climate change mitigation.” A recent media push for an organization called Trillion Trees, relies on similar logic. Oh, if this were true. Rebuttals can be found here, here, and here. The bottom line is that the academic work behind the trillion tree solution is far from valid.
The rest of this article looks at a different reality surrounding what is called nature-based carbon dioxide removal (CDR). Nature-based CDR is anything that removes carbon dioxide from the atmosphere through natural means, be it forests or natural ecologies, soils and agriculture, or oceans.
In the last 30 years we have emitted as many greenhouse gases as in the previous 250.
This new reality is that, bluntly put, nature-based climate control could have likely been quite meaningful decades ago. In the last 30 years however, we have emitted as many greenhouse gases as in the previous 250 years. Today’s solutions are no longer those from our past. In addition to greenhouse gas emissions reduction and zero emissions by 2050, or 2035 even, we need to remove a lot of the greenhouse gas climate pollution we have emitted in the past that remains in our sky. And this, just to limit warming to 1.5 C by 2100.
Considering the climate catastrophes that are currently ramping up in extremeness, and the abrupt collapses of things like the West Antarctica, the safe level of warming is far below 1.5 C and quite possibly the level of warming that allowed all these catastrophes to start just after the turn of the century at 0.5 C.
(Important Note: Global Warming psychology says give hope! We can restore our climate with no more trouble than what we experience every year treating human sewage pollution, and it’s a lot less messy! Yes it’s a big job, but so is cleaning up the human pollution from most of the 7.5 billion people on this planet! Ew!)
U.S. national forests are dying at a rate that is twice that at which they are growing.
Currently, U.S. national forests are dying at a rate that is twice that at which they are growing and the Amazon has flipped from carbon sink to carbon source three times since 2005 in ever-increasing droughts greater than the 100-year event. Tropical forests may continue to regain their carbon storage capacity after these increasingly unprecedented drought events because they cycle organic materials very quickly, but slower cycling temperate forests have likely crossed an irreversible carbon absorption threshold and slower boreal forests are even more likely to have crossed. These forests realities combined, and when their sub-continental scale impacts are taken into the global context, carbon sequestration from forests is nothing like it was in the twentieth century when our traditional forest/climate truths were created.
In summary, the needed carbon dioxide removal (CDR) of the recent Intergovernmental Panel on Climate Change (IPCC) 1.5 C report — in addition to 80 percent emissions reductions by 2030 and net zero emissions by 2050 — is widely accepted by experts to be about 1,000 Gt by 2100, or an average of 12.5 Gt per year starting in 2020. (1) What this means is that a combination of nature-based CDR and industrial CDR is now required to meet the 1.5 C target.
The broad consensus on nature-based CDR capacity is that it is limited to 2.75 to 10 Gt per year with emphasis on 5 Gt or less, because of physical constraints and issues related to justice like needing to respect the rights of undervalued cultures where large parts of the world would be consumed by nature based CDR strategies. (See the Nature-based literature summary below.)
Because the nature-based CDR is less than what is needed to meet the 1.5 C warming target, industrial CDR required is two to five times greater than the plausible natural CDR capacity. And again, this is to limit warming to 1.5 C, with overshoot to 1.7 C in about 2070 while we get our climate reform act together.
The 1.5 C target then is more than triple the amount of warming that allowed the climate catastrophes and collapses to begin, and double the warming in 2018 of 0.82 C. In addition, extremes increase nonlinearly with more warming. In other words, a little more warming doesn’t create a little more extreme weather or ecological collapse, it creates a lot more.
The nature-based capacity evaluations that are optimistically 10 Gt per year, and realistically likely somewhere below 5 Gt CO2 per year, include: the IPCC, National Academy of Sciences, Paul Hawken’s Drawdown, and others. They are a bit light on the ocean-based CDR capacity end of the spectrum, but well represented by land-based strategies. Importantly, all look at justice issues concerning the nature-based strategies that could change land needed for other uses into things used only for carbon removal.
More carbon removal is now needed than can be satisfied by nature-based solutions.
When all things are considered, nature-based solutions are a large part of the solution and tree planting is a portion of the nature-based tool kit. But the burden is now much bigger than it was when we established the benefits of nature-based climate solutions and far more carbon removal is now needed than can be satisfied by nature-based solutions.
What to do? More than a hundred years ago when we learned that human sewage was killing millions with disease, we learned how to treat human sewage. The technology to treat carbon dioxide pollution was first used to keep our sailors safe from carbon dioxide poisoning in World War II. This technology and similar technologies are are well on their way to industrialization at large enough scales to make a difference. See here, here and here.
What we need is the will. Tell your friends. Use your voice. It may not be too late yet, but we all have to step up and allow our new climate reality to enter into the conversation. This may not happen in time frames that matter unless we all act.
Summary of nature-based CDR limits
IPCC. Of the 12.5 gt negative emissions per year required to meet 1.5 C, IPCC says enhanced natural earth systems and bio-energy with carbon capture and sequestration (BECCS) can account for five to 10 Gt annually if advanced strategies are put into place. (2)
James Hansen suggested in July 2017 that by 2100, “We conclude that 100 PgC [or 367 Gt CO2, or 4.6 gt per year from 2020 through 2100] 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.” (3)
National Academy of Sciences suggested in an October 2018 report on Negative Emissions Technologies and Reliable Sequestration that up to 10 gt CO2 per year CDR is possible, but that realistic “safe” limits, considering societal, economic and environmental impacts, reduce these quantities by half. This means that the possible maximum safe level of CDR from forests, ag and soils is 2.75 gt CO2 per year, with additional removal from BECCS and blue carbon (oceans) of 2.15 Gt CO2 per year globally. The total “safe” CDR from natural sources is then about 4.9 gt CO2, including oceans. (4)
Paul Hawken’s Drawdown, and his exhaustive description of advanced drawdown opportunities says about 10 gt negative emissions per year is possible using enhanced natural earth systems, (5) summarized in Figure 1:
The Institute for Sustainable Futures’ work, the Leonardo DiCaprio Foundation One Earth Climate Model, called a ground breaking new framework climate modeling platform, includes ocean and terrestrial conservation, reforestation, and carbon-negative agricultural practices to reach a 1.5 C goal by 2050, with 159 gt CO2 atmospheric removal, or 5.3 gt per year. The crux of this work is summarized early on page xx in the summary: “It is a technical pathway, not a political prognosis. It refers to technically possible measures and options without taking into account societal barriers.” (6)
The Rocky Mountain Institutes, Negative Emissions and Land Based Sequestration, 2018, projects negative emissions in the U.S. of 0.6 to 1.4 gt from landscape solutions (forests, soils and agriculture.) This would make up a substantial portion of the estimated annual 7–10 Gt CO2 global sequestration that could be delivered through landscapes. (7)
Links and expert comments
Original paper – Bastin et al., The Global Tree Restoration Potential, Science, July 5, 2019.
Eureka Alert Press Release – https://www.eurekalert.org/pub_releases/2019-07/ezdo-tgt062719.php
1) Best-case Emissions Reductions Scenario… The IPCC 1.5 C Report, 1.5 C scenario allows warming to overshoot to about 1.8 C around 2075, return to 1.5 C by 2100 and not reverse below today’s temperature until well into the twenty-second century. This scenario includes 1,000 gt cumulative CDR by 2100, or 12.5 gt average annual CDR from 2020 to 2100, plus global warming emissions reductions of 80 percent by 2050 and 100 percent (net zero) by 2050.
Chapter 2, IPCC SR15, Mitigation Pathways Compatible with 1.5 C in the Context of Sustainable Development, October 2018. Page 128, Figure 2.13(c).
2) IPCC 1.5 C Plausible Negative Emissions… Holding the global temperature to 1.5 C by 2100 with overshoot to between 1.7 and 1.8 C, or below 1.5 C through the twenty-first century, requires 4.4 gt negative CO2 emissions per year from AFOLU (agriculture, forestry and other land uses), plus 5.7 gt negative CO2 emissions from bio-energy with carbon capture and storage (BECCS), for a total of 10.1 gt negative CO2 emissions pre year through 2100.The potential for CDR is the amount of CDR plausible given socio, economic and environmental considerations. For example, BECCS estimates of potential CDR of 0.5 to 5 gt per year requires 25–46% of arable and permanent crop area in 2100; Aforestation and reforestation have the potential of 0.5 to 3.6 Gt per year; Soil carbon sequestration with agriculture strategies and biochar are 2.3 to 5.3 gt per year. For enhanced weathering of minerals, ocean alkalinization, and ocean fertilization, IPCC says low evidence and low confidence with a wide range of values from less than 1 gt to 95 gt per year. These strategies do not include work on socio, economic and environmental risks. Direct air capture of carbon dioxide with chemicals is presented with an equally large range of $20 to $1,000 gt and no estimate of the plausible CDR quantity. The challenge with direct air capture is that the current industrial scale trials are not represented in the literature because 1) the private organizations involved are protecting their trade secrets and 2) this work does not include the 2018 David Keith paper on Carbon Engineering’s $100 per ton existing process.
Chapter 2, IPCC SR15, Mitigation Pathways Compatible with 1.5 C in the Context of Sustainable Development, October 2018. Table 2.4.
3) Hansen, 4.6 gt CO2 CDR using enhanced forests, agriculture… James Hansen, director of the NASA Goddard Institute for Space Studies, or the US climate modeling agency, says that “an appropriately ambitious estimate” of drawdown of CO2 from forests, agriculture and soils is less than 5 gigatons per year globally. “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.” 100Pg C = 367 Tons CO2 or 4.6 gt CO2 per year for 80 years 2020 to 2100.
Hansen et al., Young people’s burden-requirement of negative CO2 emissions, Earth Syst. Dynam., July 18, 2017, page 591, paragraph 1.
4) The National Academy of Sciences Negative Emissions Technologies report in 2018 says the safe, equitable atmospheric carbon dioxide removal with natural terrestrial Earth Systems enhancements is 2.75 gt CO2 per year globally… The Report “highlights” states that up to 5 gt atmospheric CO2 removal using forests and agriculture enhancements is plausible, “However, attaining these levels would require unprecedented rates of adoption of agricultural soil conservation practices, forestry management practices, and waste biomass capture. Practically achievable limits are likely substantially less, perhaps half the 1 GtCO2/yr in the US and 10 GtCO2/yr globally.” When this logic is applied to the quantities in Table 1, the results are that half of 5.5 gt atmospheric removal are available as the description of Table 1 states, “The ‘Safe’ rate of CO2 removal means that the deployment would not cause large potential adverse societal, economic, and environmental impacts.”
Table 1 (Globally)
Afforestation/Reforestation 1 gt/yr
Forest Management 1.5 gt/yr
Agricultural Soils 3 gt/y
Total 5.5 gt/yr
Additional removal from BECCS and blue carbon (living plants or sediments in tidal marshlands, seagrass beds, and other tidal or salt-water wetlands) of 2.15 Gt CO2 per year is possible globally. The total “safe” CDR from natural sources is then about 4.9 gt CO2. The rest must come from technologies that use chemical and mechanical means, or oceans, otherwise we exceed 1.5 C goals.
Negative Emissions Technologies and Reliable Sequestration, A Research Agenda, Consensus Study Report, Highlights, National Academy of Sciences, October 2018, Summary, page 2, paragraph 2 and 3, and Table 1.
5) Drawdown, Paul Hawken, 10 Gt atmospheric CO2 removal using forest and agricultural enhancements… Paul Hawken’s exhaustive description of advanced drawdown opportunities in his book Drawdown—The Most Comprehensive Plan Ever Proposed to Reverse Global Warming says about 10 gt negative emissions per year are possible using enhanced natural earth systems, summarized in the table below:
Hawken, Drawdown—The Most Comprehensive Plan Ever Proposed to Reverse Global Warming, Penguin Books, 2017.
6) Teske’s Institute for Sustainable Futures work 2018 (DiCaprio funded) is 5.3 Gt CO2 per year for 1.5 C by 2050… The Institute for Sustainable Futures work, the Leonardo DiCaprio Foundation One Earth Climate Model, called a ground breaking new framework, climate modeling platform, includes marine and terrestrial conservation, reforestation, and carbon-negative agricultural practices to reach a 1.5 C goal by 2050, that 151.9 gt C (557 gt CO2) atmospheric removal is required, or 18.5 gt CO2 per year, to limit warming to 1.5 C by 2050. (page xviii, paragraph 3) From their Press release, “Citing a growing body of research, we show that using land restoration efforts to meet negative emissions requirements, along with a transition to 100% renewable energy by 2050, gives the world a good chance of staying below the 1.5°C target.” VERY IMPORTANT – This work explicitly states that their 1.5 C scenario, “Refers to technically possible measures and options without taking into account societal barriers.” (page xx, paragraph 2)
It’s an advanced look at renewables given their recent jump in penetration that is not included in previous modeling. It does not include evaluation of carbon dioxide removal considerations for social, economic and environmental considerations and only devotes only 14 pages out of 491 to non-energy emissions. Their needed 18.5 gt CO2 removal annually is way above the plausible drawdown capacity of earth systems alone implying a very significant need for carbon dioxide removal with chemicals, or geoengineering oceans.
Teske et al., Achieving the Paris Climate Agreement Goals, DiCaprio One Earth Climate Model, Springer Open, February 5, 2019.
See Leonardo DiCaprio Foundations One Earth Climate Model, by the University of Technology Sydney (UTS), the German Aerospace Center (DLR), and the University of Melbourne.
7) Rocky Mountain Institute… This report focuses primarily on how natural climate solutions could be deployed and contribute to emissions reduction goals in the United States, which has projected negative emissions technologies contributing 0.6–1.4 Gt CO2 sequestration annually by 2050. This would make up a substantial portion of the estimated annual 7–10 Gt CO2 global sequestration that could be delivered through landscapes.
Rocky Mountain Institute, Negative Emissions and Land Based Sequestration, November 2018.
[Bruce Melton, a longtime contributor to The Rag Blog and guest on Rag Radio, is a professional engineer, environmental researcher, filmmaker, author and CEO of the Climate Change Now Initiative in Austin, Texas; the oldest, independent climate science education organization in the world founded in 2005. The Climate Change Now Initiative is a nonprofit outreach organization reporting the latest discoveries in climate science in plain English, using global warming psychology to communicate this new science on the right side of the brain. The Initiative’s science reporting, films, music and images of climate impacts happening now can be found at ClimateDiscovery.org.]