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Don’t plant trees to address climate change. Instead, leave fossil fuels in the ground

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Last week, the New York Times published an article that argues that, “The science says that spending precious dollars for climate change mitigation on forestry is high-risk”. It is written by Nadine Unger, an assistant professor of atmospheric chemistry at the School of Forestry and Environmental Studies, Yale University.

Unger’s article triggered responses from forest scientists and climate scientists, a BINGO, a consulting firm, and lots of people on twitter. (Unger has deleted her twitter account.)

Unger’s article, “To Save the Planet, Don’t Plant Trees“, argues that protecting forests and planting trees is not an effective solution to climate change.

Unger’s argument is based on two main points:

  1. The albedo effect: Forests are dark and absorb more of the sun’s heat than agricultural fields which are lighter and reflect the sun’s heat. (That’s why dark snow in Greenland is such a problem.)

    But as Unger points out, climate scientists have calculated that “planting trees in the tropics would lead to cooling, but in colder regions, it would cause warming”.

    CIFOR’s Louis Verchot points out that,

    Stopping tropical deforestation and increasing tree planting in REDD+ countries, where the albedo effect is smaller than the carbon effect, makes sense from an energy balance point of view.

    A commentary by Dan Nepstad of the Earth Innovation Institute and colleagues notes that forests create water vapour and clouds, especially in the tropics. This increases sky albedo (i.e. increases reflectivity), a point that Unger doesn’t consider in her article.

  2. Volatile organic compounds: Trees emit gases that help protect them from stresses like heat and insect attack. These volatile organic compounds combine with pollution from fossil fuels to form methane and ozone, both of which are powerful greenhouse gases.

    But as Doug Boucher from the Union of Concerned Scientists writes, “reducing fossil fuel pollution is the most direct and effective way to reduce this effect, not blaming the forest”.

    The second question relating to volatile organic compounds is whether cooling effect of fewer gases being released is as big as the warming caused by the release of carbon from forests when they are converted to cropland.

    In Unger’s recent paper in Nature Climate Change, she calculates the cooling effect of converting forest to cropland between 1850 and 2000 as −0.11 ± 0.17 W/m2. That is, somewhere between -0.28 (cooling) and +0.06 (warming). The IPCC Fifth Assessment Report provides global radiative forcing values of land use change for CO2 of between +0.17 and 0.51 W/m2, and for albedo of −0.15 ± 0.10 W/m2.

    Michael Wolosin at Climate Advisers sums up:

    So not only is the carbon effect three times bigger than the atmospheric chemistry effect, the underlying article can’t even say with statistical certainty the direction of the atmospheric chemistry effect – whether it is in the direction of causing warming or cooling.

So far, so good, then. A climate scientist who focusses on atmospheric chemistry wrote an opinion piece in the New York Times arguing against planting trees to address climate change. Lots of people responded on the article.

But there’s an elephant in the room. Unger’s conclusion happens to be right: “spending precious dollars for climate change mitigation on forestry is high-risk”.

Climate change is only one of the many reasons for protecting forests and for planting trees. To address climate change we need to stop digging out and burning fossil fuels.

On the EDF website, Steve Schwartzman argues that,

Emissions from tropical deforestation are, from the perspective of the atmosphere, just the same as emissions from burning fossil fuels – carbon that was wood, coal, oil or gas is turned into CO2 and released to the atmosphere.

While it is true that the carbon emitted from burning forests is chemically the same as the carbon emitted from burning fossil fuels, from the climate perspective they are different.

Carbon stored underground as fossil fuel is stable. It will only enter the atmosphere if it is dug out and burned. Carbon stored in forests, soils, and peatlands is difficult to measure, is not stable, and can far too easily enter the atmosphere.

Climate change makes the problem worse, by making the carbon stored in forests even less stable. Carlos Nobre, Brazil’s National Secretary for Research and Development Policies, in a recent interview with CIFOR notes that,

[T]here are areas in the Amazon in which a repeated cycle of deforestation, regrowth and fire has led to a landscape that is highly degraded. It’s an impoverished kind of savannah. I think that’s what the forests of the future will look like if climate change is not checked.

So even if we did stop cutting down trees, the changing climate means that the forests will go up in smoke.

To address climate change, we need to reduce greenhouse gas emissions. Deforestation is one source of greenhouse gas emissions, but what proportion of total emissions comes from deforestation?

In her New York Times article, Unger repeats a common mistake:

“Deforestation accounts for about 20 percent of global emissions of carbon dioxide.”

It’s easy mistake to make. The UN-REDD website, for example, makes the same false claim.

Researchers from Winrock International and Woods Hole Research Center came up with a figure of 10% based on data from between 2000 and 2005. Since then emissions from fossil fuels have increased, meaning that deforestation now accounts for an even lower percentage of global emissions.

This graph from the Global Carbon Project illustrates the proportion of greenhouse gas emissions that come from land-use change since 1960:

In 2013, the figure was 8%.

Nadine Unger has written a response to the criticism. She provides sources for statements she made in the New York Times article and clarifies that,

Protection and restoration of tropical and other forests is essential regardless of their effects on climate. Currently, global climate modeling is not sufficiently advanced to predict reliably the effects of changing forests on the global average surface temperature.

The primary key to solving the global climate problem is the transformation of our energy system into one that does not use the sky as a waste dump for our greenhouse gas pollution.

Exactly. To address climate change we need to leave fossil fuels in the ground.

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  1. The global C project data show that indeed while an important segment of the climate change delegations was discussing forest issues, the rise of fossil fuel emissions, esp. in China, wiped out any gains on controlling greenhouse gasses made by forest protection. Recent insights into ‘rainbow water’ and a role for trees and forests in stimulating rainfall recycling may mean that the forest-climate debate is overly ‘carbonized’ and a more direct climatic significance of restoring and retaining tree cover lies elsewhere. See: Current Opinion in Environmental Sustainability 6, 41-47.

  2. To Save the Planet, Don’t Plant Trees….
    Ms. Nadine Unger was drunk when she wrote this article?

  3. Thanks for responding to Dr. Unger’s confusing op-ed.

    How forests are managed really matters. Forest conservation helps store carbon and reduce warming, while logging emits carbon and amplifies warming. We need to BOTH reduce fossil energy use AND conserve forests.

    More info: Heiken, D. Myths & Facts on Forest, Carbon and Global Warming slide show clarifying many misconceptions about forests, logging, and carbon:

  4. @Chris Lang, Yes I did.



    Although I agree with the conclusions of Nadine Unger, I do not agree on many phrases that have led to these conclusions.

    Marco Sassi .
    Associazione Foreste per Sempre (Forests forever) – Italy

  5. @Marsco Sassi (#5) – Sorry about my slightly snarky last reply. It seems as though we agree. Thanks for clarifying!

  6. The large majority would no doubt agree that fossil fuels are the main cause of global warming. Reducing their consumption would obviously mitigate carbon emissions. But this is incidental to the argument, particularly as we have abjectly failed to reduce fossil fuel consumption. Of course we cannot solve our climate problems solely by planting trees and protecting forests, but neither does anyone seriously suggest that we can. Nonetheless, forests can be part of any solution, while additionally providing many co-benefits, at local, regional and global scales. Moreover, we have been far more successful in reducing deforestation and rehabilitating forests than we have in reducing fossil fuel use. We should not talk forests down when they are a credible and realistic, albeit partial, solution to a complex and multifaceted problem.

  7. Whilst I go with the “leave fossil fuels in the ground” thesis – it’s one of those “no-brainer”s, isn’t it? – I really dislike “The Albedo Effect” used to justify the agro-industrial environment of the temperate regions. I does not and can not and neither groups, individuals nor corporation should be allowed to get away with it.

    There is just as great a need to reforest temperate zones – such as the UK – as there is to reforest and stop deforestation of the tropical regions.

    PS – I agree fully with Jaboury’s comment, above, and remember that, over the last ten to twenty THOUSAND years mankind has HALVED global forest cover. The process has been very long running – it just accelerated recently.

  8. The argument presents a false dichotomy between the solutions of renewable energy and reforestation.

    One third of Earth’s land is arid and sparsely populated. Most of this arid land — about one fourth of the land on Earth — can be forested. Planting and managing these forests as a source of net-zero carbon fuel to replace coal and natural gas, and as a means to limit forest fires and sequester carbon to restore a moderate, balanced climate, can also provide habitat for wildlife and most humans, and provide food, building materials, water resources, soil, beauty, and employment; and it can do all this within the lifetimes of most persons born today.

    There are currently more than 200 million persons around the world looking for work, which is a sufficient work force to accomplish this task. We can begin by focusing on providing work for the unemployed among the more than 50 million refugees — the persons in most urgent need of the dignity of work and home.

    These forests will soon pay for themselves, but soon isn’t soon enough: the challenge is covering the costs for the first 20-40 years while the first plantings mature, and this is in fact what is stopping wide-scale managed forestation today. The solution is a new, parallel glocal economy that works right beside the existing global economy but consists of a network of powerful and autonomous community currencies.

    These powerful currencies don’t yet exist because they need to have their value backed in ways that keep them circulating locally at sufficient volume to build self-sustaining local communities. Most alternative currencies today are backed by promise of exchange with national currency, however that facility tends to remove local currency from circulation in marketplaces. The backing necessary to produce powerful local currencies can be secured by their local communities through the offer of a significant discount on one or two essential commodities produced in each community. For example, in the poorest communities, where limited access to electricity or water might be the biggest problem — even for those whom have money — individuals can be paid with this local currency to pedal generators and pump water to charge LED lights and to access and filter potable water — both of which are proven profitable enterprises in these circumstances; and the electricity and water produced could be discounted 50% when traded for local credit. As access grows, the marketplace would grow, which would further increase demand for the renewable resources in a continuous, virtuous cycle.

    The credit can be created in online trading platforms that already exist and are available to the public globally at no or little cost; and the discount that’s offered on the locally-selected commodities will provide the demand for the credit and for the commodities that permits use of the credit employing workers, including employing the mangers of the platforms. This demand for credit can also impel and empower the development and conservation of all local human and natural resources: not only water and energy, but food, sanitation, housing, education, day care, and more — including forestation as part of longterm development — everything that can be accomplished with local resources when there is sufficient access to energy, credit and a network of mutual, skilled support.

    This strategy will still require initial/start-up funding with national currencies to pay for equipment and labor until production of the local commodities selected for discount secures the value of the local credit, and to import technologies that can’t be produced locally. However, this parallel glocal network can meet most of that need by permitting individuals to volunteer their help and to exchange the necessary national currency for local credit, which cannot be exchanged back to national currency but can provide them with community credit to obtain the discount on the selected local commodities.

    The result of this new approach will be a world filled with self-sustaining, forested communities that are also able to provide renewable resources and customers to the global marketplace. And a world filled with such prosperous, sustainable communities will be a prosperous and sustainable world.

    A detailed analysis, including sample pilots for both emerging and developed economies, with benefit-cost analyses, is available free at through a Creative Commons Attribution-NonCommercial-ShareAlike license.

  9. just stop popping out babies for a generation or two. Carbon problem solved. Your not special, neither would your children be and they will have an even more pathetic existance than you. Get a bike, get a life, get off the bloody tv and internet. Stop buying solid wood products from stupid adverts, and stop buying shite you don’t need.

  10. I find it completely irresponsible to encourage people not to plant trees. The high rates of deforestation ocurred in the southern hemisphere for the last decades might in fact be the main contributor to global warming. I understand the effects of a lower albedo from the establishment of massive forest plantations, but trees capture CO2 and the more individual trees we have here and there, the better for all of us. Roughly speaking, the amount of CO2 released after combusting one gallon of gasoline is about the same amount captured by one average tree in one year. The battle is still on, and we are losing it. For that, lets encourage tree-planting activities and not supress them. Thank you.

  11. Please read the publication below for a better perspective. Thanks.

    “How forestry in the southern hemisphere can help address desertification and global climate change. Journal of Forestry 113(1): 72-74. (2015)”