To Tree or Not to Tree is not the Question

August 19, 2019

Photo by Stefan Rahmstorf

A lot of talk about planting trees as a magic bullet solution to climate change. Well, it’s not magic.
But that doesn’t mean it’s not a good idea.

By the way, we should be doing all we can to preserve the forests we have, as well.


Ethiopians planted 353 million trees in 12 hours, part of a 4 billion tree-planting campaign to fight deforestation and climate change, Minister for Innovation and Technology Getahun Mekuria said.

A world record was set, according to Mekuria, as Ethiopians heeded Prime Minister Abiy Ahmed’s ambitious plan to roll back years of drought and scanty rains that the United Nations says has left some 3.8 million people in immediate need for assistance.

The Horn of Africa nation started rationing power on May 17 due to low-water levels at the Gibe 3 hydro-electric dam and discontinued power export to neighboring Sudan and Djibouti.

Ethiopia, Africa’s second most populous nation with 100 million people, had forest cover of just 14% of its territory in 2018, according to the United Nations.Ethiopians planted 353 million trees in 12 hours, part of a 4 billion tree-planting campaign to fight deforestation and climate change, Minister for Innovation and Technology Getahun Mekuria said.

A world record was set, according to Mekuria, as Ethiopians heeded Prime Minister Abiy Ahmed’s ambitious plan to roll back years of drought and scanty rains that the United Nations says has left some 3.8 million people in immediate need for assistance.

Kathleen Parker in the Washington Post:

At the moment, our biggest problem — climate change — could be ended by simply planting trees. Okay, so 1 trillion trees, according to a Swiss study published this month in the journal Science. But how hard is that, really?

Most people know that trees are good for them. They absorb carbon dioxide, thus purifying the air for our breathing pleasure. Carbon dioxide is also one of the main greenhouse gases, which trap heat in the atmosphere, leading to rising temperatures and climate change.

Estimates are that about 15 percent of emissions come from deforestation. Trees also curb other harmful gases, such as sulfur dioxide and carbon monoxide, again releasing pure oxygen into the air. If Congo’s 150 million hectares of forests were lost, it would generate about three times the world’s total emissions in 2012.

But scientists, including Thomas Crowther, a co-author of the trillion-tree study, were quick to point out that planting trees alone wouldn’t work. And how does one go about planting 1 trillion trees? And where should they be planted?
Although tree-planting is a simple solution — effective and cheaper than any other remedy currently in circulation — it isn’t simply a matter of planting trees helter-skelter. A forest in the wrong place could have detrimental effects by upsetting the ecological balance.
But this seems a relatively easy obstacle to clear.
The countries with the most land available for building forests are Russia, China, Canada, Australia, Brazil — and the United States. The Switzerland-based researchers found that adding 1.2 trillion trees would reverse 10 years’ worth of harmful emissions. Over the decades, Crowther says those new trees would absorb about 200 billion tons of carbon from the atmosphere.

Several countries have signed up for reforestation, including the United States, which has seen an increase in its forestland, thanks in part to the Forest Service’s tree-planting initiatives. But we have to figure that the wreath of rainforests that wrapped around the globe until relatively recently was surely there for good reason. Satellite images show that the Amazon rainforest — the world’s largest — is disappearing at the rate of 1 1/soccer-field-size parcels per minute. What such decimation means to the planet’s future can’t be good — unless ridding the world of humans is Earth’s ultimate survival measure.
No trees, no birds, no bugs, no bees, no food, no humans. That’s pretty simple, too.

The Guardian:

As trees grow, they absorb and store the carbon dioxide emissions that are driving global heating. New research estimates that a worldwide planting programme could remove two-thirds of all the emissions that have been pumped into the atmosphere by human activities, a figure the scientists describe as “mind-blowing”.
The analysis found there are 1.7bn hectares of treeless land on which 1.2tn native tree saplings would naturally grow. That area is about 11% of all land and equivalent to the size of the US and China combined. Tropical areas could have 100% tree cover, while others would be more sparsely covered, meaning that on average about half the area would be under tree canopy.
The scientists specifically excluded all fields used to grow crops and urban areas from their analysis. But they did include grazing land, on which the researchers say a few trees can also benefit sheep and cattle.

“This new quantitative evaluation shows [forest] restoration isn’t just one of our climate change solutions, it is overwhelmingly the top one,” said Prof Tom Crowther at the Swiss university ETH Zürich, who led the research. “What blows my mind is the scale. I thought restoration would be in the top 10, but it is overwhelmingly more powerful than all of the other climate change solutions proposed.”
Crowther emphasised that it remains vital to reverse the current trends of rising greenhouse gas emissions from fossil fuel burning and forest destruction, and bring them down to zero. He said this is needed to stop the climate crisis becoming even worse and because the forest restoration envisaged would take 50-100 years to have its full effect of removing 200bn tonnes of carbon.


In recent weeks, a new study by researchers at ETH Zurich has hit the headlines worldwide (Bastin et al. 2019). It is about trees. The researchers asked themselves the question: how much carbon could we store if we planted trees everywhere in the world where the land is not already used for agriculture or cities? Since the leaves of trees extract carbon in the form of carbon dioxide – CO2 – from the air and then release the oxygen – O2 – again, this is a great climate protection measure. The researchers estimated 200 billion tons of carbon could be stored in this way – provided we plant over a trillion trees.

The media impact of the new study was mainly based on the statement in the ETH press releasethat planting trees could offset two thirds of the man-made CO2 increase in the atmosphere to date. To be able to largely compensate for the consequences of more than two centuries of industrial development with such a simple and hardly controversial measure – that sounds like a dream! And it was immediately welcomed by those who still dream of climate mitigation that doesn’t hurt anyone.

Unfortunately, it’s also too good to be true. Because apples are compared to oranges and important feedbacks in the Earth system are forgotten. With a few basic facts about the CO2 increase in our atmosphere this is easy to understand. Mankind is currently blowing 11 billion tonnes of carbon (gigatonnes C, abbreviated GtC) into the air every year in the form of CO– and the trend is rising. These 11 GtC correspond to 40 gigatons of CO2, because the CO2molecule is 3.7 times heavier than only the C atom. Since 1850, the total has been 640 GtC – of which 31 % is land use (mostly deforestation), 67 % fossil energy and 2 % other sources.

All these figures are from the Global Carbon Project, an international research consortium dedicated to the monitoring of greenhouse gases.
The result is that the amount of COin our air has risen by half and is thus higher than it has been for at least 3 million years (Willeit et al. 2019). This is the main reason for the ongoing global warming. The greenhouse effect of COhas been known since the 19th century; it is physically understood and completely undisputed in science.

But: this COincrease in the air is only equivalent to a total of just under 300 GtC, although we emitted 640 GtC! This means that, fortunately, only less than half of our emissions remained in the atmosphere, the rest was absorbed by oceans and forests. Which incidentally proves that the COincrease in the atmosphere was caused entirely by humans. The additional COdoes not come from the ocean or anywhere else from nature. The opposite is true: the natural Earth system absorbs part of our COburden from the atmosphere.

Conversely, this also means that if we extract 200 GtC from the atmosphere, the amount in the atmosphere does not decrease by 200 GtC, but by much less, because oceans and forests also buffer this. This, too, has already been examined in more detail in the scientific literature. Jones et al. 2016 found that the amount of carbon removed from the atmosphere amounts to only 60% or less of the negative emissions, when these are implemented on the background of a mitigation scenario (RCP2.6). 

We can also compare the “negative emissions” from tree planting to our other emissions. The 200 GtC would be less than one third of the 640 GtC total emissions, not two thirds. And the authors of the new study say that it would take fifty to one hundred years for the thousand billion trees to store 200 GtC – an average of 2 to 4 GtC per year, compared to our current emissions of 11 GtC per year. That’s about one-fifth to one-third – and this proportion will decrease if emissions continue to grow. This sounds quite different from the prospect of solving two-thirds of the climate problem with trees. And precisely because reforestation takes a very long time, it should be taboo today to cut down mature, species-rich forests, which are large carbon reservoirs and a valuable treasure trove of biological diversity.

There is another problem that the authors do not mention: a considerable part of the lands eligible for planting are in the far north in Alaska, Canada, Finland and Siberia. Although it is possible to store carbon there with trees, albeit very slowly, this would be counterproductive for the climate. For in snowy regions, forests are much darker than snow-covered unwooded areas. While the latter reflect a lot of solar radiation back into space, the forests absorb it and thus increase global warming instead of reducing it (Bala et al. 2007Perugini et al. 2017). And increased regional warming of the Arctic permafrost areas in particular would be a terrible mistake: permafrost contains more carbon than all trees on earth together, around 1,400 GtC. We’d be fools to wake this sleeping giant.


18 Responses to “To Tree or Not to Tree is not the Question”

  1. Wayne Appleyard Says:

    Thanks for blogging this. You highlighted the most important line:

    because the forest restoration envisaged would take 50-100 years to have its full effect of removing 200bn tonnes of carbon.

    Tree planting will do little to reduce CO2 in the near future. A while ago I looked at what the typical site plan 3 year old tree would do:

    If you assume a sapling is planted when it is three years old and we are looking at our 10 year window it only sequesters 338 lbs of CO2.
    If you plant the typical young 1 1/2″ diameter tree specified for tree replacement in a lot of ordinances it will only sequester 550 lbs of CO2 over that 10 years.

    If you look at 2050 the sequestering of that 3 year old tree goes up to 2550 lbs of CO2.

    Realistically the trees that will be planted are not the 3 year old nursery trees but smaller ones which will sequester even less and have a higher mortality rate.

    And what about infestations. recently it was stated that the NJ pine Barrens may be lost to a beetle that is moving north.

    Yes we need to plant trees, but only for our grand children’s sake. What we really need to do is to stop combusting things.

  2. Keith McClary Says:

    That’s 17 million square kilometres. We also need:

    “The amount of ‘bioenergy with carbon capture and storage’, or BECCS, required in coming decades will depend on how quickly we sideline fossil fuels and shrink our carbon footprints.

    The new IPCC report, for example, outlines two scenarios based on the reasonable assumption that the world will continue to be dominated by “resource-intensive consumption patterns,” as least in the coming decades.

    Capping global warming at 1.5 C under these circumstances would require converting some 7.6 million square kilometres (km2) -– more than double India’s land mass –- to BECCS. Even if temperatures were allowed to climb twice as high, the report concluded, biofuels would still need to cover some 5 million km2.”


    ” ‘We project that under ‘business-as-usual’ growth, 9.8 billion people by 2050 would require 56 percent more food relative to 2010,’ said Fred Stolle, an adjunct professor at Johns Hopkins University and co-author of the UN-backed report, Creating a Sustainable Food Future.

    ‘That would require clearing nearly six million square kilometres’ –- ten times the area of France—’of additional forests for conversion to agriculture,’ two-thirds for pasture land, and one-third for crops, he told AFP.”

    Add half a million for solar panels, but they can go in deserts.

  3. rsmurf Says:

    We don’t need any more land to plant trees, every house that does not have any trees… plant some, every freeway/road that has no trees between the lanes… plant some, every median in every town that has no trees… plant some. Plant gardens everywhere! They don’t take up that much space. Every parking lot could be a solar farm, every garage, every roof.

    • Keith McClary Says:

      Unfortunatly, trees in populated areas can require expensive maintenance.

      Why Can’t We Plant Trees in Highway Medians?

      Vegetation Control for Safety, A Guide for Local Highway and Street Maintenance Personnel

      A friend has an enormous old tree, trunk 1m in diameter. Good on him, you say. But it’s dying and dropping branches on his neighbour’s yard and garage. He can’t afford to have it removed.

      • rsmurf Says:

        Gee then lets just cut all trees down!! Sorry thats a bunch of crap!! Trees have been growing on this planet for millions of years WITHOUT MAINTENANCE. Yes we can plant trees in the highway medians, half the medians have them right now! Im not interested in VEGETATION CONTROL FOR SAFETY. Poor baby dropping branches on something, WAH. I guess this crap you suggested is WAY more important the the survival of the human race. GET A LIFE.

        • Keith Omelvena Says:

          Reminds me of the tree lined street in my town. Many residents were whining for years about “falling leaves”, although it was a tree lined street before most of the were born, let alone bought a house there. Eventually the mature trees were cut down and the stumps ground to mulch. The spindly replacement trees are olives. Guaranteed to fail, as the soil is poorly drained and saturated for weeks at times. But hey, no leaves.

        • Keith McClary Says:

          My relative was next to the trashed car half an hour before the tree came down.

          You have the same expense for removing old urban trees before or after they do damage. Of course, there is no expense if they are in a remote forest. What is the carbon footprint of removing this tree and repairing the houses and utility lines and replacing the car?

    • rhymeswithgoalie Says:

      Hey, trees are why I don’t put solar panels on my roof. Having a tree-shaded home was a popular recommendation for lowering your A/C bills.

      • rsmurf Says:

        Well put them on racks somewhere on your property , that’s what I did. And I keep my 90% shade on my house.

      • rsmurf Says:

        If its totally not feasible to put on panels, make sure you buy your power from a wind or solar source!

        • greenman3610 Says:

          many utilities have these programs available

        • rhymeswithgoalie Says:

          I pay the extra for the Austin Energy Green Energy (wind) program.

          How often do you have to clean your solar panels?

          • rsmurf Says:

            Never. Tried an experiment where I cleaned a couple to see if there was a difference, couldn’t see a diff. Haven’t experimented in a while, I think ill try again it hasn’t really rained in about 2 months there may be a buildup. But the cold really helps, below freezing they really crank it out, biggest solar days are in the winter, very random but big.

          • rsmurf Says:

            Im on a coop I have no options, only what they send me. But I produce almost all I use so its not that big a deal.

  4. Brent Jensen-Schmidt Says:

    Growing trees remove Co2 from the atmosphere and have multiple other benefits. Goody! Can they save the planet is a matter of opinion. Definitely helps and does not hurt. As for problems, find solutions like, if an area is unsuitable, do not plant! Not damn rocket science. Best and most economical geoengineering process available with multiple other benefits.
    Is a outfit here called Trees for Life. One pays for the privilege of receiving around 650 tree seeds and material to grow seedlings. When grown, one plants them out, usually on a ‘farm’. A pal doing it takes around 12 man days (person days) of very hard work. Have watched chicks reforesting, in the BC Rockies, slapping in seedlings at one a minute, just to be different.

  5. grindupbaker Says:

    My solution is to kick all the humans out of the bit of Earth just south of the Canadian border yet north of Mexico & make it a dense forest. Other humans will have other suggestions of course but mine is optimal for helping planet Earth.

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