The Pros and Cons of Planting Trees To Address Global Warming

Yves here. Time for a change in programming, so trees.

By Bruce Lieberman. Originally published at Yale Climate Connections

It seems like such a simple, straightforward, empowering idea: plant trees – a lot of trees – all over the world, and watch the planet’s temperature fall.

Who doesn’t love a tree or two, even far more – the right tree in the right place?

Along with the refreshing shade they provide on hot days, trees of course also store carbon, and they’ll suck it right out of our fragile atmosphere as they grow. Who could argue with more trees, more forests – more shade! – in a warming world? Nary a soul, one suspects, whether of conventional “tree hugger” category or rabid climate science detractor.

Earlier this year, the one-trillion tree campaign was big news at the World Economic Forum in Davos, Switzerland. Salesforce founder Businessman Marc Benioff announced at the meeting that his company will “support and mobilize the conservation and restoration of 100 million trees over the next decade.”

Back in Washington, D.C., President Trump and Republican lawmakers said they too support the international campaign – although Arkansas Republican Rep. Bruce Westerman came under fire for proposing a “Trillion Trees Act” that would pair a commitment to planting trees witha planto increase logging on public lands. Numerous other Republican representatives are endorsing the trees effort.

Cautions Against Just Randomly Digging and Planting

Over the past few weeks, chatter has picked up that planting trees is only one piece of the puzzle when it comes to combating climate change. Trees are a good thing, but:

  • We also need to protect existing forests – the Amazon, for example.
  • We need to ramp up wind, solar, and geothermal energy.
  • We need to burn less fossil fuel.
  • We need to eat more of the right foods and less of the wrong ones and, above all else, eat sustainably.
  • We need higher vehicle-mileage standards and more electric cars.
  • We need to get our act together so we can better adapt to rising seas, more droughts and wildfires, and unpredictable swings in weather.

Like other initiatives to tackle climate change, planting trees requires some forethought. Recent news coverage of the trillion tree campaign points to several things people should be thinking about before digging and planting.

Authors of a 2019 study from the Swiss research university, ETH Zurich, estimated that the planet can support about 2.5 billion more acres of newly planted trees – without tearing down cities and doing away with farms. And they say those trees could store about 200 gigatons of carbon (GtC) once they mature. That’s equal to one-third of all the carbon that humans have emitted into the atmosphere as carbon dioxide pollution, the authors claimed. The New York Times summarized the study last year.

Researcher: ‘Nations absolutely should plant and protect as many [trees] as possible. … But it’s also a limited and unreliable way of addressing climate change.’

Scientist Zeke Hausfather, long a regular contributor to Yale Climate Connections, suggested in a series of tweets at the time that the study was misleading on a few counts. For one thing, cumulative emissions from land use and burning fossil fuels were closer to 640 GtC, “so removing 200 GtC would represent one-third of historic emissions.” Hausfather also pointed to the practical and economic challenges of planting trees on every acre of available land.

India is intimately familiar with this challenge. Last summer the country planted hundreds of millions of trees as part of an initiative to keep one-third of its land area covered in trees. But the nation’s high population and rapid industrialization pose challenges to sustained reforestation. Only about 60% of the saplings are expected to survive – the rest succumbing to disease and a lack of water.

A Skeptical Science article by Dana Nuccitelli, a regular contributor to Yale Climate Connections and an environmental scientist, cites additional studies that have raised several other key points. Among them:

  • Tundra and boreal regions unpopulated by trees play an important global role in reflecting energy from the sun back into space. Planting trees in these regions would darken landscapes at these high latitudes, causing them to absorb energy from the sun rather than reflect it – ultimately contributing to higher global temperatures and offsetting cooling created by planting trees.
  • The ETH Zurich researchers mistakenly considered natural savannas, grasslands, and shrublands as places where forests could be restored.
  • And in their ETH Zurich study, they estimated a carbon sequestration rate of 0.22 GtC per million hectares (i.e., for every 2.47 million acres). But 0.22 GtC is twice the amount cited by previously published estimates.

Trees Deserve a ‘Moment’ of Fame, but Keep Reality in Mind
So while the right kinds and numbers of tree species in the right places have lots of appeal, big questions remain over exactly what can be accomplished by planting one trillion trees – and whether it may cause more harm than good.

James Temple, senior editor for energy at MIT Technology Review, summed up the view of many experts in a January 28 piece when he wrote:

“It’s great that trees are having a moment. Nations absolutely should plant and protect as many as possible. … But it’s also a limited and unreliable way of addressing climate change.”

Temple raised a few more important points, some of which have been echoed elsewhere. Among them: trees take time to grow and reach maturity – decades and even centuries for redwoods and other behemoths that can store massive amounts of carbon. If you think you’re going to immediately offset your carbon footprint from flying across the country by planting a tree … think again.

Another point Temple made: You really have to work the numbers to get a true sense of the challenge. For example, he wrote, the U.S. produced 5.8 billion gigatons of carbon dioxide emissions in 2019. To offset that much CO2 pollution, you’d have to plant a forest – and wait for it to fully mature – that is more than twice the size of Texas.

The one-trillion tree campaign raises still more questions for forest ecologists – one of them having to do with biodiversity. If the campaign results in what are essentially tree plantations lacking biodiversity and genetic variation, often referred to as monoculture, those artificial forests won’t get very far.

“People are getting caught up in the wrong solution,” Forrest Fleischman of the University of Minnesota told The Verge in late January. “Instead of that guy from Salesforce saying, ‘I’m going to put money into planting a trillion trees,’ I’d like him to go and say, ‘I’m going to put my money into helping indigenous people in the Amazon defend their lands.’ That’s going to have a bigger impact.”

A campaign to plant “one trillion trees” sounds ambitious, it sounds daring, and it sounds exciting. And in many ways it could be all of those. But keep in mind that since 2015 and just in the Sierra Nevada – that sliver of mountain habitat that runs along the spine of California –nearly 150 million trees have died, victims of drought, disease, and invasion by beetles. Warmer winters have contributed to a population explosion of these destructive insects, and it’s a story being played out across the American West where forest fires are growing in frequency and intensity.

So maybe we can plant a trillion trees around the globe. But if we don’t do much else about climate change, will we just be fueling the fire?

So maybe we can and should plant a trillion trees around the globe. Go for it. But a wide array of experts insist that if we don’t also take numerous other actions to address climate change – specifically including major cuts in fossil fuel emissions and in particular carbon dioxide – we may just be fueling the fire.

In the end, it comes down to more trees andlots of other actions, not to more trees or.

More To Read

Tree planting is Trump’s politically safe new climate plan,” Vox, Feb. 4, 2020

Trump and the trillion trees,” The New York Times, Feb. 5, 2020

What’s better than planting a trillion trees? Protecting the forests while we are at it.,” The New York Times, Feb. 10, 2020

Planting trees won’t save the world,” The New York Times, Feb. 12, 2020

Republican lawmakers introduce trillion trees act to combat climate change,” Reason, Feb. 13, 2020

1 trillion trees: What would it take, how would it work, and is it even worth it?,”Fast Company, Feb. 19, 2020

Panel battles over tree-planting legislation,” The Hill, Feb. 26, 2020

A trillion trees not enough to fix climate crisis, critics say,” PhysOrg, Feb. 27, 2020

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34 comments

  1. grayslady

    I’m surprised the author doesn’t address one of the obvious benefits of trees–shade. Homes with lots of large trees shading the house substantially reduce, or eliminate, the need for air conditioning.

    Reply
    1. PlutoniumKun

      They have huge local benefits (as urbanists in traditional hot countries have known for years), see all the lovely mature trees in mature public squares all around the Mediterranean).

      But sometimes there can be surprising resistance. A friend who was involved in a project to put street trees up in a suburb in a lower income community in the English Midlands found protestors stopping the works. The reason people opposed them was ‘that burglars could use them to spy on us’. Seriously.

      Reply
      1. Joe Well

        All the trees on the 140-year-old, formerly tree-lined street (silver maples) where my mother lives are gone.

        The second to last was chopped down because its roots were destroying pipes.

        The last one was sickly and the heavy dead branches were a menace.

        But now that I write this I wonder why none of us took the leadership to find out if there are species of trees that don’t cause these problems? Is there a worldwide guide for what trees to plant near buildings?

        Reply
        1. PlutoniumKun

          You would think there would be, but these things are very hit and miss – its really down to local governments understanding what works in their local climatic conditions and fits into maintenance works – but sometimes this ‘institutional memory’ gets lost. I grew up on a street with beautiful Japanese cherry trees – but they were all cut down in the 1990’s as they were destroying the pavements (cherry trees have very large lateral roots). But recently I noticed that some were being replanted – and then were quickly removed again, presumably someone realised the mistake.

          Climate change is impacting things as well – trees which might once have been considered suitable/unsuitable may become useful in some cities. The London Plane, for example, used to only grow well in a line (as the name suggests) north of London, but I think now grows well over most temperate areas.

          Changing technology also has an impact. I was in the UK in 1990 when wholesale removal of street trees was required because the then Tory government, in its eternal wisdom, gave private utilities the right to lay fibre optic cable in shallow trenches on public pavements. The result was cutting machines slicing the vital lateral roots of entire streets of mature trees (contrary to what is often thought, including by road engineers, tree roots mostly don’t go down – the most important roots grow laterally, just under the soil surface).

          Reply
        2. Odysseus

          One would think that conduit of some kind (metal pipe, or concrete, brick, or stone structure) would protect pipes from tree roots. Simply digging a trench and dropping the pipe into the bottom is probably not a best practice.

          Reply
        3. Anon

          There is NO worldwide guide to the planting of trees other than the one indicated in the article: The right tree in the right place. This requires scientific knowledge of climate, botany, soils, and societal infrastructure in a specific location.

          For instance: those silver maple trees have characteristics that are inappropriate for the setting you described:

          Acer saccharinum—Very fast-growing. Leaves are green on top and silvery-white on the underside, shimmering and dancing in the breeze. Tolerates a wide range of soil conditions. Because of a vigorous root system, plant 10′ or more from sidewalks, drives, foundations, and sewer lines. Grows to 50′ to 80’with spread 2/3 of height to wider than the tree is tall. (plant zones 3-9)

          Those maples were likely selected for their rapid leaf growth without considering their invasive root growth. While soil type and quantity can limit the size and health of any tree the silver maple is prone to weak branching (breakage) when constrained by the planting environment. The monoculture of maples likely encouraged their decline to disease. Urban arborists are employed by smart municipalities for this reason.

          Reply
        4. Edr

          I have a book on local trees and plants for South Florida, and it gives details about invasive roots and trees that don’t damage pipes. I’m sure your community has a set of similar books that would help.

          Reply
    2. clarky90

      Elton Trueblood:

      “A person has made at least a start on discovering the meaning of human life, when they plant shade trees, under which they know full well, they will never sit.”

      Reply
  2. Bee

    Thanks so much for posting this, Yves. This is sort of like Jean Giono’s “The Man Who Planted Trees and Grew Happiness” writ super-huge! I’m a landscape historian and tree lover. and completely agree that while planting more trees is good and necessary the WEF and Benioff approach won’t make it. In my view, this is just more of the same old top-down, everything and everyone is just a fungible piece of data mind-set, which is pretty well what got us into this disaster in the first place. Hausfather and Nuccitelli start pointing the way out of this one-size-fits-all solution, and Fleischman focuses on where it needs to go. Specific places, specific geographical and climatic conditions. As Korzybski would have said, come back down that ladder of abstraction to each physical reality. This is not that. Something we as a culture would do well to learn.

    Reply
  3. PlutoniumKun

    Lots of governments (including my own, in Ireland), are using commercial tree planting as a ‘cover’ for CO2 emission reduction. They are now profoundly embarrassed to find that conifer plantations in temperate climates can in some circumstances actually increase CO2 emissions, especially when planted on natural peat. Not that its stopped them doing it.

    Planting even on urban fringes can be problematic. 20 years ago I was helping with an NGO planting urban forestry on former industrial land around the West Midlands in the UK. Despite using best available techniques, there was a very high failure rate. Disturbed land can take decades to restore itself to a healthy balance (it does with time, many fine Victorian parks in UK cities are on former collieries). I saw one whole year of planting die in a hot summer – the degraded soils couldn’t hold moisture, so turned essentially to dust, killing all the young trees.

    I think a general rule of thumb is that you should only plant trees in an area if they grow naturally if you fence the area off from grazers. Its astonishing how quickly many temperate areas will naturally afforest if you keep sheep and deer away. The resulting forest is far more likely to be a genuine carbon sink than commercially available species.

    Reply
  4. CanCyn

    Maybe it isn’t an issue because I haven’t seen It mentioned but I worry about the water required to get young trees established. Trees not well watered and watered properly when they are young just don’t mature well. They can’t withstand drought because their roots aren’t established deeply or strongly.
    Water scarcity is going to be a problem too. Am I overthinking this?
    Am Inov

    Reply
  5. Carla

    In the U.S., attempts to restore the tree canopy in urban and inner-ring suburban communities have bumped up against significant resistance from residents. A major reason: NOBODY ASKED THEM IF THEY WANTED A TREE. Trees are fabulous, but they shed leaves that have to be raked and cleaned out of urban gutters. Their roots can damage basements and sewer lines. In storms, they sometimes fall, destroying cars, homes and even unwitting people.

    But in the end, “the rejections had more to do with how the tree-planters presented themselves and residents’ distrust of city government than it did with how residents felt about trees.”

    https://grist.org/article/why-detroit-residents-pushed-back-against-tree-planting/

    Turns out it’s not only upper-middle-class and rich white folks who want to have a say in what’s done in their neighborhoods. Shocker!

    Reply
    1. Brooklin Bridge

      An issue with trees in residential suburban areas is roof top solar panels being shaded out. This is largely a question of the right kind of trees and trimming from time to time, but it needs to be taken into consideration in the planting. I wonder what simply letting one’s lawn be handled by nature, and cutting down or trimming sun blocking trees where appropriate, would provide in these locations?

      Reply
  6. JohnMc

    The forests of the tropical Amazon store their carbon in the biomass above ground in trees. On the other hand, grasslands in temperate climates store carbon below ground in the soil, hence there are areas like iowa that have (had) soils 12 feet deep. Grain farming that tills the soil oxidizes that stored carbon in a form of carbon mining. Perennial crops such as forage sequester carbon from the air.

    Time to bring back the prairie, not to try and create a rain forest in a temperate zone. Anyone interested in more of this, i recommend Richard Manning’s ‘grassland’.

    Reply
    1. drumlin woodchuckles

      This is what farmer Gabe Brown in North Dakota and some lonely few other farmers are doing a version of. Land either under no-till cover crop which is then roller-crimper smash-downed and row-crop seeds planted through the smash-downed cover plants, and then several years of perennial pasture on that field or fields till the ongoing rotation again calls for row-crops through smash-downed cover crops.

      Here are images of the roller-crimper machinery used for smashing down the cover crop.
      https://images.search.yahoo.com/search/images;_ylt=AwrJ7J0jE3VedyAAwDNXNyoA;_ylu=X3oDMTEybDZjNXI4BGNvbG8DYmYxBHBvcwMxBHZ0aWQDQjk1MzZfMQRzZWMDc2M-?p=roller+crimper&fr=sfp

      And here is a bunch of Gabe Brown videos. Each video is a little different. If you enJOY watching these, you slowly get different bits of information.
      https://video.search.yahoo.com/search/video;_ylt=AwrJ6ydqE3VeeycAVWdXNyoA;_ylu=X3oDMTEybDZjNXI4BGNvbG8DYmYxBHBvcwMxBHZ0aWQDQjk1MzZfMQRzZWMDc2M-?p=youtube+gabe+brown&fr=sfp

      If you don’t enJOY these videos, Gabe Brown’s ” Ted Talk” is a simplest possible version of his main points for layfolk.

      And then there is silvo-pasture, including silvo-pasture with coppiceable nut-fruit shrubs and/or little trees.

      Reply
      1. Billy

        In addition to natives for wildlife, please plant fruit trees. A few afternoons’ work twelve years ago and ever since we’ve had all the citrus we can eat or increasingly give away.
        We have been and now are giving away grocery bags full of oranges and lemons to neighbors and never have to worry about vitamin C shortages, nor lack of refreshing drinks.
        Yesterday a distant neighbor brought over ten cans of sardines to trade in gratitude for all the fruit we have given them. Zero effort on our part other than walking down the hill, kicking the tree and gathering up the fruit that falls off.
        Note: Sour and pithy grapefruit often ages and becomes sweeter after a couple week’s storage.

        Reply
    2. Brooklin Bridge

      I was hoping someone would mention the prairie and grasslands. From an admittedly superficial vantage point, it seems as though tree planting is often just a political football to throw out there.

      Reply
  7. Trick Shroadé

    My county in Maryland’s DC suburbs has a program where builders and developers who cut down trees in order to build new homes must pay in to a fund that then provides shade trees free-of-charge to home owners who want them planted on their property. I have 3 lovely new shade trees now! And they’re a decent size when the plant them – probably close to 10 feet tall!

    Reply
  8. Brooklin Bridge

    …the U.S. produced 5.8 billion gigatons of carbon dioxide emissions in 2019.

    That’s 5.8 billion billion tons of carbon dioxide per year, no?. Can that be right?

    According to the USGS, in 2017,

    The U.S. Energy Information Administration estimates that in 2017, the United States emitted 5.1 billion metric tons of energy-related carbon dioxide, while the global emissions of energy-related carbon dioxide totaled 32.5 billion metric tons.

    I can’t believe we increased totals from 2017 to 2019 by that much. I could easily be missing something (metric tons for instance, energy related?), or, the above estimate of a billion billion could be a typo but it seems way high…

    Reply
  9. Copeland

    I’m as green as it gets and I love trees, but being green also means exploring non fossil-fuel based ways of heating your house. Passive solar design and heating have been almost completely forgotten since the 70s, and passive solar requires as much winter sun as possible.

    Trees and solar energy collection (both Thermal and Photovoltaic) do not mix very well, especially if the energy is being collected at ones place of residence. In most cases in cities, if you plant your trees where they will not impact your solar collectors, they will impact your neighbors solar collectors.

    This stuff is complicated. These days I mostly think city parks and wilderness areas should be filled with trees, not so much neighborhoods.

    Reply
    1. Zamfir

      Keep in mind, a trillion trees worldwide means hundreds of trees per household. There is no point in adding a few trees within the built environment. At least when it come to carbon sequestering, the trees might be nice for other reasons.

      Reply
      1. drumlin woodchuckles

        It has been common wisdom in the mid-latitudes that deciduous trees planted on the sun side of a house or building ( southside north of the equator, northside south of the equator) cast a cooling shade on the house in summer, drop their leaves and let most of the wan weakly warming sunlight of winter through their bare branches to hit the walls or go in the windows.

        Some passive tree-cooling in summer, some passive tree-permitted heating in the winter. If fears of global warming super storms keep rising, and one fears that a tree or trees will fall on a house, perhaps strategically-placed lines of bamboo which will shade a house in summer though I don’t know how well they will permit passage of sunlight in winter. But they won’t blow down onto your house in a superstorm.

        Reply
  10. Copeland

    I’m as green as it gets and I love trees, but being green also means exploring non fossil-fuel based ways of heating your house. Passive solar design and heating have been almost completely forgotten since the 70s, and passive solar requires as much winter sun as possible.

    Trees and solar energy collection (both Thermal and Photovoltaic) do not mix very well, especially if the energy is being collected at ones place of residence. In most cases in cities, if you plant your trees where they will not impact your solar collectors, they will impact your neighbors solar collectors.

    This stuff is complicated. These days I mostly think city parks and wilderness areas should be filled with trees, not so much neighborhoods.

    Reply
    1. Susan the other

      There are so many sites all around the world where reclamation is necessary to clean up all sorts of toxics that we should start there planting our trees. We will need to dig up and haul away the polluted soil in any event and the most logical thing to do is plant trees which will replenish the soil, mitigate global warming immediately as well as store carbon indefinitely. That combines 2 problems in one solution. That’s where I’d start.

      Reply
        1. drumlin woodchuckles

          Sanitary landfills. Or maybe vast polluted soil pyramids in the desert.

          Or maybe plant and harvest succeeding generations of certain metal-sucking dynamic accumulator plants right there where the contaminated soil is. Let the plants uptake the contaminant ( works for some metals). Burn the plants. Plant and burn , plant and burn. The toxic metals will remain in the ash. They will take up a tiny fraction of the space of the plants, let alone the soil itself. Maybe the ash will be concentrated enough in certain metals so as to be worth refining for the metals.

          Reply
  11. rexl

    People say about various trees, “they are messy.” Well, yes, I say they drop leaves and seeds. It’s not like cigarette butts and beer cans.
    Of course, people say well they can get into the pipes, to which, I always ask, what are you, a plumber. Now with plastic, air-tight drainage pipe that problem is also receding.

    Reply
  12. Tony Wright

    It is extremely important to plant trees, however not just any old trees will do.
    For example:
    Many countries have seen mass monoculture plantings of timber trees chosen on accountancy criteria i.e. How much timber and pulp can be produced in the shortest time to maximise profits. This has resulted in huge worldwide plantations of Eucalyptus globulus, the Tasmanian blue gum. I have personally seen them planted in Portugal, California and Peru. This creates two major problems:
    Fire; all Eucalypts contain volatile, combustible oils – even green they go up in massive flames. Recent horrendous bushfires here in Australia show this clearly. Portugal has had to rethink blue gum plantation policy following major fires there.
    Local ecology; Eucalypts in foreign countries are usually utterly useless to local insect, mammal, and often bird fauna.
    Protection and expansion of residual forests and woodlands of local species is therefore a much better approach.

    Reply
  13. Leo Grellede

    As usual too much saviors, no solution. Are the forests,in the future, a big achievement for next generations? Is the biodiversity a mandatory rule for a right preservation/implementation of the environment? Do we start policies for protecting as much is possible the forests we have now? Therefore we SHALL plant as many trees is possible. This is the agenda. If we discuss about electric cars, wind&solar plants…, is absolutely right but they are other useless perspectives toward the agenda: let’s plant trees.

    Reply
  14. Don Scott

    We in Canada and the USA have to stop cutting old growth forests. They are the super CO2 sinks, absorbing hundred if not thousands times more CO2 than new seedlings for decades if not a century or more. Why does. British Columbia’s progressive NDP government, supported by the Greens, continue allowing the decimation of the tiny bit of Old Growth Forests remaining. Last summer I took three kayak trips into inlets in NW Vancouver Island, Broken Island Group, Nuchatlits and Quastsino. All the mountains were subject to huge clear cuts. Many recent. These ancient forests giant trees are our biggest, most efficient carbon absorbers.
    When planting, focus on native species. They have the insects that attract the birds in your ecosystem, otherwise you have green voids that lack diversity needed for a healthy ecosystem.
    And above all, slash our carbon emissions. Buy EVs instead of pick-ups, fly less, avoid cruise ships (neither an issue with the pandemic) and count your carbon as carefully as you count dollars. Treat your carbon emissions like contaminated surfaces, avoid them.

    Reply

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