Planting trees won’t solve climate change

Back in 2009, I described various ways to try to deliberately engineer the Earth system to reduce the severity of climate change and noted:

The first way to do this is to encourage the growth of biomass. This is relatively easy, but has limited potential. Biomass is like a giant carbon cushion: it can be thick or thin, but it cannot keep growing forever. Increasing the amount of biomass on Earth could draw down the amount of CO2 in the atmosphere a bit, but only if we also manage to cut our greenhouse gas emissions to practically zero.

Now that Prime Minister Trudeau has pledged to plant 2 billion trees as a climate solution (using expected pipeline revenue, to try to justify Canada’s continuing fossil fuel expansion) it’s worth having a post specifically on the limited ability of tree-planting to combat the problem.

A recent Slate article notes:

The notion that any significant percent of the carbon humanity spews can be sucked up by planted trees is a pipe dream. But it got rocket boosters in July, when Zurich’s Crowther Lab published a paper, in Science, proclaiming that planting a trillion trees could store “25 percent of the current atmospheric carbon pool.” That assertion is ridiculous, because planting a trillion trees, one-third of all trees currently on earth, is impossible. Even a start would require the destruction of grasslands (prairies, rangelands, and savannas) that reflect rather than absorb solar heat and that, with current climate conditions, are better carbon sinks than natural forests, let alone plantations. Also, unlike trees, grasslands store most of their carbon underground, so it’s not released when they burn.

The Crowther paper horrified climate scientists and ecologists, 46 of whom wrote a rebuttal, explaining that planting trees in the wrong places would exacerbate global warming, create fire hazards, and devastate wildlife. They rebuked the authors for “suggesting grasslands and savannas as potential sites for restoration using trees” and for overestimating by a factor of 5 “potential for new trees to capture carbon.”

Counter-intuitively, growing trees in order to burn them could actually be more of a climate solution, provided we develop the carbon capture and storage technology and infrastructure needed to bury the resulting CO2.

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here.

16 thoughts on “Planting trees won’t solve climate change”

  1. I hope that as these different methods of combatting climate change are developed. That the long term effects are considered.

    I was reading in passing in the Economist how nuclear power was placed alongside renewables as sources of energy that are fossil energy free.

  2. Doesn’t this just mean that the process needs to be about rebuilding diverse ecosystems which can be resilient in the face of things like pests and fires and store carbon long-term? It won’t correct for continuing to use fossil fuels forever, but it could help mitigate how harmful the pollution we have already caused will be.

  3. Justin Trudeau likes to say, promise and do nice things. He wants to be remembered as a good and caring guy. Although his decisions, especially economic ones, may not be smart for the future, his heart seems to be in the right place. Like BC’s Dr. Bonnie Henry, he handled the Covid-19 crisis calmly and perhaps contributed to its gentler course in our country.

  4. Climate change: Planting new forests ‘can do more harm than good’

    Rather than benefiting the environment, large-scale tree planting may do the opposite, two new studies have found.

    One paper says that financial incentives to plant trees can backfire and reduce biodiversity with little impact on carbon emissions.

    A separate project found that the amount of carbon that new forests can absorb may be overestimated.

    The key message from both papers is that planting trees is not a simple climate solution

  5. A key area of controversy is that many countries attempt to offset the emissions from burning fossil fuels by claiming that carbon is absorbed by land within their borders. U.N. rules allow countries, such as China, Russia and the United States, each to subtract more than half a billion tons of annual emissions in this manner, and in the future could allow these and other countries to continue to release significant emissions while claiming to be “net zero.”

    In other words, much of the gap is driven by subtractions countries have made on their balance sheets. Many scientists say countries should only claim these greenhouse gas reductions when they take clear action, as opposed to claiming natural forest regrowth unrelated to national policies.

    And some of this carbon absorption isn’t even happening — or at least not on the scale that countries assert.

    Malaysia, for example, released 422 million tons of greenhouse gases in 2016, placing it among the world’s top 25 emitters that year, according to data compiled by the Food and Agriculture Organization of the United Nations. But because Malaysia claims its trees are consuming vast amounts of CO2, its reported emissions to the United Nations are just 81 million tons, less than those of the small European nation of Belgium.

  6. Many countries and businesses plan to deploy mass reforestation as part of net-zero plans. Experts say this is problematic for two reasons.

    The first is simple science: Earth’s plants and soil already absorb enormous amounts of manmade CO2 and there are signs that carbon sinks such as tropical forests are reaching saturation point.

    “The concern is that the biosphere is turning from a sink to a source by warming itself,” said Allen.

    “So relying on the biosphere to store fossil carbon is really daft when we may well need all the nature-based solutions we can find just to keep the carbon content of the biosphere stable.”

    Teresa Anderson, senior policy director at ActionAid International, said relying on land-based carbon sequestration was “setting Earth up for a rude awakening”.

  7. Temporary nature-based carbon removal can lower peak warming in a well-below 2 °C scenario

    Meeting the Paris Agreement’s climate objectives will require the world to achieve net-zero CO2 emissions around or before mid-century. Nature-based climate solutions, which aim to preserve and enhance carbon storage in terrestrial or aquatic ecosystems, could be a potential contributor to net-zero emissions targets. However, there is a risk that successfully stored land carbon could be subsequently lost back to the atmosphere as a result of disturbances such as wildfire or deforestation. Here we quantify the climate effect of nature-based climate solutions in a scenario where land-based carbon storage is enhanced over the next several decades, and then returned to the atmosphere during the second half of this century. We show that temporary carbon sequestration has the potential to decrease the peak temperature increase, but only if implemented alongside an ambitious mitigation scenario where fossil fuel CO2 emissions were also decreased to net-zero. We also show that non-CO2 effects such as surface albedo decreases associated with reforestation could counter almost half of the climate effect of carbon sequestration. Our results suggest that there is climate benefit associated with temporary nature-based carbon storage, but only if implemented as a complement (and not an alternative) to ambitious fossil fuel CO2 emissions reductions.

  8. When it comes to forests, the carbon-offset market is also unable now to factor in what is known as permanence. Replacing a diesel bus with an electric one probably removes emissions forever—with any luck there will be no diesel buses left to buy when the electric one reaches the end of its life—but a patch of forest can be cleared or burnt in the next decade, or even the next week. How can the market ensure that offsets purchased today have enduring effects? And in Brazil and elsewhere, programmes to reforest or plant new forests also come with a leakage problem: protecting one patch of land might simply encourage deforestation elsewhere.

    All these problems apply to the existing, voluntary carbon markets. An economy ticket on a flight from London to New York generates approximately 600kg of CO2; offsets for that carbon can be purchased for as little as a few dollars through commercial tree-planting schemes. That may ease a traveller’s conscience, but whether it will protect the climate is far from certain. Over the coming fortnight, delegates at COP26 will try to reach agreement on guidelines to assure permanence and account for additionality, in hopes of creating a model that can be emulated in the voluntary markets.

    That is all to the good. There is indeed no poem lovely as a tree, and carbon offsets, and the forests they may cause to be planted or protected, can help slow and even stop climate change. But for that to happen the world’s leaders will need to demand far less popular measures as well, like ending the use of fossil fuels and transforming farming. Climate models show that ecosystem sinks will be most effective at absorbing CO2 if warming remains in the range of the Paris goals. If temperatures soar, as looks likely, carbon-rich tropical ecosystems will dry out, burn and become carbon sources rather than sinks. Trees cannot solve the climate crisis. Only people can.

  9. How phantom forests are used for greenwashing – BBC News

    Capturing carbon by increasing forest cover has become central to the fight against climate change. But there’s a problem. Sometimes these forests exist on paper only – because promises have not been kept, or because planted trees have died or even been harvested. A new effort will now be made to track success and failure.

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