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Can planting trees save our climate?

Filed under: — stefan @ 16 July 2019

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 release that 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 CO2 – 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 CO2 in 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 CO2 has been known since the 19th century; it is physically understood and completely undisputed in science.

Room for more trees? Sheep grazing on deforested land in New Zealand. (Photo S.R.)

But: this CO2 increase 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 CO2 increase in the atmosphere was caused entirely by humans. The additional CO2 does not come from the ocean or anywhere else from nature. The opposite is true: the natural Earth system absorbs part of our CO2 burden 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. 2007, Perugini 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.

And there are other question marks. Using high-resolution satellite maps and Google Earth, the researchers have analyzed where there is a suitable place for forests where none is currently growing, leaving out farmland and cities. With the help of machine learning technology, natural areas around the world were evaluated to determine the climate and soil conditions under which forests can thrive. The free and suitable land areas found in this way amount to 1.8 billion hectares – as much as the combined area of China and the USA.

But for many of these areas, there are probably good reasons why there is currently no forest. Often they are simply grazing lands – the authors respond that they have only assumed loose tree cover there, which could even be beneficial for grazing animals. The Dutch or Irish pastures would then resemble a savannah. Nevertheless, there are likely to be considerable obstacles of very different kinds on many of these areas, which are not apparent from the bird’s-eye view of the satellites. The authors of the study also write that it is unclear how much of the areas found would actually be available for planting.

Therefore, I’d still consider it optimistic to assume that half of the calculated theoretical planting potential can be realized in practice. Then we’re talking of 1-2 GtC of negative emissions per year. But that is precisely what we will need urgently in the future. The current global CO2 emissions can be reduced by 80-90 % through transforming our energy, heating and transport systems – but there will remain a rest that will be hard get rid of (e.g. from agriculture, industrial processes and long-haul flights) and that we will have to offset in order to stabilize the global climate.

The study by the ETH researchers has another important result that has hardly been reported. Without effective climate protection, progressive warming will lead to a massive loss of existing forest cover, especially in the tropics. At the same time, the models are not yet able to make reliable statements on how forests can cope with new extremes, fire, thawing permafrost, insects, fungi and diseases in a changing climate.

Global warming threatens massive forest losses (red), especially in the tropics. Fig. 3 from Bastin et al., Science 2019

The massive planting of trees worldwide is therefore a project that we should tackle quickly. We should not do that with monocultures but carefully, close to nature and sustainably, in order to reap various additional benefits of forests on local climate, biodiversity, water cycle and even as a food source. But we must not fall for illusions about how many billions of tons of CO2 this will take out of the atmosphere. And certainly not for the illusion that this will buy us time before abandoning fossil fuel use. On the contrary, we need a rapid end to fossil energy use precisely because we want to preserve the world’s existing forests.

Links

Would a large-scale tree restoration effort stop climate change? Forest expert Marcus Lindner from EFI points to the fires in Russia and the success story in China.

How to erase 100 years of carbon emissions? Plant trees-lots of them. National Geographic shows the importance of indigenous peoples as guardians of the forest.

Restoring forests as a means to many ends The commentary in Science on the Bastin study revolves around the question of how sustainable reforestation can be designed with multiple benefits beyond mere carbon storage.

Tree planting ‘has mind-blowing potential’ to tackle climate crisis Guardian

Analysis: How ‘natural climate solutions’ can reduce the need for BECCS Last year Carbon Brief prepared this analysis of how much carbon mitigation potential may be expected from “green” solutions like tree planting or biochar.

223 Responses to “Can planting trees save our climate?”

  1. 1
    John Pollack says:

    “Without effective climate protection, progressive warming will lead to a massive loss of existing forest cover, especially in the tropics.”

    How true! But it’s even more difficult than that. Worldwide, the climate will be changing across existing and newly-planted forests. The result will be that the trees composing the current forest will often be poorly adapted for the future climate. This means greater tree mortality, insect and disease problems, fires due to a higher percentage of dead wood in forests, etc. So, even if the future climate in an area still allows a forest, the individual trees composing the forest will be on a rapid replacement cycle, with diminished capacity for carbon storage.

  2. 2
    Richard Rood says:

    Thanks for this Stefan. There are a number of if we “just” did this solutions to climate change that are very popular right now. With regard to trees and this report, I immediately recalled the work of Robert Jackson et al., esp., Trading Water for Carbon with Biological Carbon Sequestration (Science, 2005). When considered in the system as a whole, there are many limits that are revealed. Not to mention that behavioral and policy challenges are far more formidable than technology and scientific challenges.

  3. 3
    Jef says:

    It is all about healthy forest not trees. The difference between trees and forest is massive. All effort should go toward preserving forests we have and reclaiming/expanding on them.

    You can’t plant a forest but we must do the best we can. That and stoping the madness of consumption.

  4. 4
    Nemesis says:

    @Stefan Rahmstorf

    Thanks a lot for presenting a realistic perspective on planting trees for co2 absorbtion. This is the most crucial point to me:

    ” But we must not fall for illusions about how many billions of tons of CO2 this will take out of the atmosphere. And certainly not for the illusion that this will buy us time before abandoning fossil fuel use. On the contrary, we need a rapid end to fossil energy use precisely because we want to preserve the world’s existing forests.”

    I see a huge gap between certain geoengineering plans (that’s exactly what large scale tree planting ect means) and real world fossil fuel policy. As long as there is no significant co2 emissions reduction (and that means a radical systemic shift of vast proportions, avoided for many decades so far), any geoengineering scheme will fail for certain. It seems like the powers that be hop from one technofix idea to the next just to avoid any substantial system change, that game is going on for many decades now and the longer it goes on, the harder it will be for any engineering plan to be successful.

    And there is another crucial point:

    ” At the same time, the models are not yet able to make reliable statements on how forests can cope with new extremes, fire, thawing permafrost, insects, fungi and diseases in a changing climate.”

    We see that all over Europe right now, millions of trees are dying because of the ongoing severe drought resp insects and deseases, new planted trees are dying as well as young trees are most vulnerable.

    Does anyone expect Nature to be some kind of funny Lego construction kit to suit capitalist market needs and some sort of waste dump for co2, plastic and what have you? Think again:

    Nature is a cooking pot, ready to eat you.

  5. 5
    Russell says:

    The Guardian ran my response to Damian Carrington’s piece on 8 July.

    In addition to the Arctic warming risks Stefan points out, i noted the area involved in the plan rivals that of Arctic sea ice- adding millions of square kilometers of dark trees exacerbates the problem of global albedo loss.

    https://vvattsupwiththat.blogspot.com/2019/07/climate-change-tree-plantin-g-and.html

  6. 6
    Climate State says:

    The Man Who Planted Trees (1987) https://www.youtube.com/watch?v=KTvYh8ar3tc

  7. 7

    “There are a number of if we “just” did this solutions to climate change that are very popular right now.”

    What are the classic Kubler-Ross stages of grief? Ah, yes: denial, anger, bargaining, depression and acceptance. Maybe those “if we just” ‘solutions’ are manifestations of ‘bargaining.’ We’ve certainly had our share of both denial and anger.

  8. 8
    mike says:

    It almost seems like we are just going to have to bite the bullet and figure out a way to cut our carbon emissions by at least 80%. How inconvenient is that?

    I have a friend who swears that all we have to do is go after the 70 to 100 corporations that are responsible for most of the emissions. I think he is following this line of thought:

    https://eand.co/climate-change-isnt-your-fault-it-s-capitalism-s-c7cf340007c4?fbclid=IwAR3mC5WIApKf6oxH4pjLsuPQrMq8s2dlZM7G9lv9wn_HEZ0Mdaa-zBtP5tM

    I suspect this is another over-simplification of the problem and the ways we might address it effectively.

    Cheers

    Mike

  9. 9

    “The massive planting of trees worldwide is therefore a project that we should tackle quickly.” Did a “not” get omitted there?

  10. 10
    Bryan says:

    Why do people keep taking Nature seriously as a source of science

  11. 11
    Dan Miller says:

    When looked at from a systems perspective, the main reason we have climate change is that we have taken vast amounts of carbon that were previously outside of the biosphere (e.g., underground oil, coal, and natural gas deposits) and we extracted them and then burned them and put that carbon into the biosphere (into the atmosphere, oceans, plants, and soils).

    To really address climate change, we must take that excess carbon and remove it from the biosphere by injecting it back underground or by making it inert by, for example, turning it into rock.

    While planting trees is a great thing to do, as others have pointed out, you are not really removing the carbon from the biosphere by growing trees. In fact, these trillion new trees will be impacted by drought, floods, heat, extreme weather, disease, bark beetles, etc. and will, therefore, give much of their carbon back to the atmosphere — at the worst possible time! (as climate impacts really start to kick in).

    As the post calls out, about 31% of excess atmospheric carbon comes from land use changes and growing trees can help offset that. But we are going to need to get serious about Direct Air Capture and other mechanical and natural techniques to draw down carbon from the atmosphere.

  12. 12

    Excellent post, Stefan, and thank you very much for doing the work to be quantitative. I tried to address some of this, but your calculations are very handy. It is so good for true experts to chime in as these. Professor Glen Peters dropped in and corrected a mistake I made with respect to clear air capture, because I forgot, as you pointed out above, that simply scrubbing a unit of atmospheric CO2 neglects the partial pressure from reservoirs in soils and oceans. I have ever been grateful for the correction!

    I think this underscores the complexity of the problem. No climate leader, whether the late Stephen Schneider or the late Wally Broecker, ever had enough time to delve into the complicated contributions from civilization and agriculture and industry in any single session.

    I am concerned that the present embrace of Allan Savoury-style non-quantitative holistics amplifies what might be called wishful environmentalism. Like it or not, ultimately this a science-informed engineering problem, with tradeoffs and complications, and it will not be dealt with by such pursuits that hope will triumph over evidence. (Countering such is the purpose of my personal blog.)

    To the degree to which we control our own destiny, how this turns out and how badly it gets quickly is entirely within our control. On the other hand, I detest notions that extermination of ourselves or, especially, of the biosphere is a possible outcome. Sure, there are uncertainties, and, sure, the dissolution of civilization is one of the options on the table. But given the rapid adaptation of ecosystems and species to our already present changes — signals to me of climate change as persuasive as observables in the climate system — I don’t think the biosphere is under much threat. There will be “species rotation”, no doubt.

    I do agree arresting deforestation and arresting development like suburban sprawl are both key to working on land use change, as well, incidentally, as limiting inland risk to weather changes brought about principally by Clausius-Clapeyron and Arctic amplification. But that is nowhere enough, and I think people, in the words of Professor Emily Shuckburgh of the BAS, don’t grasp the level of ambition needed to resolve this.

    Still, we try. And I am not about to give up.

    Thank you so much.

  13. 13
    Russell says:

    !0

    They could be Bayesians, Bryan, but it probably has more to do with Nature‘s strict corregendum and retraction policy.

  14. 14
    Robert Tulip says:

    Useful analysis of climate arithmetic. Excess C = 640 GT, growing by 10 GT/y. Current BAU/Paris Accord projections for 2030 are for growth by 15-16 GT/y.

    The role of ocean sinks means we must remove about 35 GTC/y, including emission reductions, which at present are -0.5 GTC/y, in order to shift planetary trajectory toward cooling.

    As proposed in this article, the world could theoretically scale emission reduction up to about 8 GTC, maybe a bit more (despite the conflict, cost and delay that such efforts would involve). That is still less than a quarter of needed removals.

    It is therefore essential to recognise that geoengineering technologies of carbon removal must be deployed, aiming to remove 30 GTC/y, requiring urgent field trials.

    Land based forests are marginal by comparison to ocean potential. Key methods are carbon removal could be biochar, large scale ocean based algae production, iron salt aerosol and limestone for concrete, all of which offer potential to scale bigger faster and cheaper than land forests.

    This article, like most climate analysis, neglects the area, energy and resources of the world ocean as the key decisive factors that can be utilised to stabilise and restore the climate.

    The best way to use forests to fix the climate is to focus on the ocean using marine permaculture to grow seaweed and algae at industrial scale, funded by sale of produced commodities. ARPA-E is funding some excellent projects in this practical space.

  15. 15
    BJ Chippindale says:

    More trees can’t do it alone. All of us knew that, but it is extremely good for the understanding to be quantified. Thanks Stefan.

    The response we have to have now is “all of the above”.

    The one answer I am particularly curious about is the assertion by Alan Savory that restoring the large herds and managing them properly can reverse desertification. It looks good and I haven’t seen the gotcha for it if there is one. So if anyone cares to enlighten me I’ll be listening.

    https://www.youtube.com/watch?v=vpTHi7O66pI

  16. 16

    I wonder like to know how you calculate the amount of CO2 that trees would absorbe. For CO2 dissolving in oceans, it might be a chemical equilibrium even if ocean ecosystems take CO2 out of it. Is it also the case for forests? Even at preindustrial CO2 concentrations, trees would grow quite well, and the CO2 taken out by trees could be linear with trees number and total weight.

    [Response: You just estimate how big the trees grow, half of the dry wood weight is carbon. -Stefan]

  17. 17
    J4Zonian says:

    Forestry strategies like this, that are indeed as much about halting or even reversing deforestation as about increasing forest cover in new areas, have to be combined with the transformation of chemical industrial agriculture into small-scale, low-meat perennials-based organic permaculture. Industrial ag releases soil organic matter (carbon) into the atmosphere; organic methods sequester carbon. With that addition to the lands being maintained as forest or forested/reforested, we have a considerably larger capacity for negative emissions. Combining forestry and ag in edible forest gardens–food, fiber and material production systems of up to 7 vertical layers–will allow even more sequestration and higher yields in more resilient systems.
    https://www.treehugger.com/lawn-garden/forest-garden-500-edible-plants-takes-few-hours-work-month.html?utm_source=TreeHugger+Newsletters&utm_campaign=6ab8a50c03-EMAIL_CAMPAIGN_11_16_2018_COPY_01&utm_medium=email&utm_term=0_32de41485d-6ab8a50c03-244061621

    These strategies will not be enough on their own to ensure survival of civilization, even with rapid reduction of fossil fuel use, increase in energy conservation, efficiency, etc. Dramatic reduction in meat-eating and luxury crops by the rich, reduction of logging, and other changes in our way of life will be necessary.

  18. 18
    David B. Benson says:

    Here is a link to a BNC Discussion Forum thread which contains references to related articles and peer reviewed papers:
    http://bravenewclimate.proboards.com/thread/694/trillions-trees

    (You may comment there as ‘guest’ or request to register, which involves a delay.)

    In particular, I point out that the Ornstein et al. paper on the irrigated afforestation of the Sahara and Australian outback was extensively discussed here on Real Climate when it first appeared 9 years ago. In the nonce it has been cited at least 38 times; one of those subsequent papers is referenced in the BNC Discussion Forum thread on this topic.

    Many have commented without, it appears, understanding the first thing about sylviculture in arid lands. As a starter one might care to learn about the Sewa Oasis deep in the Egyptian desert; palm trees farther than the eye can see.

    As for cost, the current proposed budget for the US DoD is $730 billion. Some fraction of that will surely suffice to begin planting trees.

    This will surely work, can begin right away and gainfully employ some of the myriads with not enough to do.

    [Response: I happen to have been at the Siwa Oasis in the early 1980s. Sure, where there is enough ground water available you can do a lot with irrigation. But it has its problems like salinization and soil deterioration. It certainly is not just a matter of planting seedlings and then a forest will appear. -Stefan]

  19. 19
    Killian says:

    Finally! Something I can sink my #permaculture teeth into!!

    Short answer, no. Caveat: But forestation and aforestation, inclusive of food forests, agroforesty, et al., can make a huge dent.

  20. 20
    nigelj says:

    Thank’s for a ‘realistic’ article on what foresty sinks can achieve. I’ve tried to point out to people that forests and soil sinks have somewhat limited potential but to no avail. It’s nice to be vindicated by the experts.

    While rates of deforestation have slowed they have far from stopped and are another impediment to developing effective forestry sinks. None of this is to dismiss the value of planting trees and stopping deforestation, we must do what we can.

    The heavy lifting will clearly have to come from renewable energy. It’s that or bust I think. Carbon capture and storage would require massive tax payer subsidies and would soak up vast quantities of resources, so relying on that would logically be a last resort, but it seems that logic plays little part in human societies.

  21. 21
    Jason Samuels says:

    Hello Stefan, thanks for this article. I agree with your critique.
    Could you please provide some sources on this quote “The current global CO2 emissions can be reduced by 80-90 % through transforming our energy, heating and transport systems”?

    Thanks again for the post,
    Kind regards,
    Jason

    [Response: Lot’s of studies on this; I added a link with that statement with an example. -Stefan]

  22. 22
    Jim Eager says:

    Mike @8 wrote: “I have a friend who swears that all we have to do is go after the 70 to 100 corporations that are responsible for most of the emissions.

    I hear that all the time from both politicians and individuals, and it is pure wishful thinking. Here in Ontario electric power generation used to be the number one emitter of CO2, but then we shut down all of our coal fired generating stations. Industry used to be the number two sector, but emission reductions and paper and steel mill closures have bumped Industry from the number two spot as well. Today the number one emitter in Ontario is transportation, meaning the biggest emitter of CO2 in Ontario is our collective tail pipe.

    Yet Doug Ford’s conservative Provincial Government eliminated the subsidy for EVs, pulled Ontario out of the cap & trade system, is fighting the Federal carbon fee & dividend tooth & nail, wants to ease vehicle mileage and emission standards, lower fuel taxes, and plans to increase highway speed limits, all of which will make transportation an even bigger CO2 emitter.

    The stupid, it burns.

  23. 23
    Aksel says:

    “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.”. If I understand this correctly, then if we remove 4 from the atmosphere, then oceans and forests will release 2? Is that due to “weakening of CO2-pressure” on forests and oceans when removing CO2 from the atmosphere?

    [Response: That’s one way of putting it. Forests, oceans and atmosphere are coupled reservoirs. If you add CO2 to the atmosphere, some of it will flow on to the other two, and vice versa. -Stefan]

  24. 24
    Killian says:

    #12, Jan, how about you not be an insulting putz to others? Wishful environmentalism? That’s ignorance, not a rational stance. You seem to believe statistics is a more powerful force than Nature itself. This is bizarre. Don’t talk down to people who know how to sequester carbon in ways you apparently believe is fantasy while you champion non-existent tech as if the threat were not existential.

    Meh.

    Ecomodernist? May as well say, “technofantasist.” Decoupling tech impacts from the environmental impacts? That’s prima facie nonsense.

    That said, I appreciate anything that helps illuminate the hard realities we face and the maths regarding CO2, emissions, ppm, etc., are useful, but set aside your arrogance because you know almost nothing you need to know to solve our problems based on your own pejorative comments regarding actual solutions and your self-labeled ideology.

    I will get to details later, but had to get your arrogance and misguided view off my chest so I could sleep.

  25. 25
    Timothy Havard says:

    European cattle are in general grazers where as most other cattle populations are grazer/browsers. The woodlands/Savannah of sub-Saharan Africa has lost it’s trees/shrubs through a combination of this cattle feeding system and deliberate lopping of green branches in the dry season for fodder-plus fire as a cultivation tool. The lose of the ground cover has accelerated surface soil erosion and accelerated water lose. The water table has been lowered by ever deeper wells and pumps killing off deep rooted trees. Nature’s defender of the woodland Savannah was the Tsetse Fly keeping sedentary farmers out from the South and cattle owners out from the North. DDT put a stop to that natural defense. Subsequently cattle have formed a walking bank especially for those wishing to hide funds swelling herds well above carrying capacity. There is little doubt that man-kind needs to plant suitable perennial vegetation to assist in the carbon sequestration program but also to assist in the reduction of soil erosion and the reestablishment of a more balance less deep water table. Looks like a feed-back system that can produce a lot more vegetation than some might think possible.

  26. 26

    This scheme seems to be of the same character as MZ Jacobson’s “Solutions Project”, now labled the “Green New Deal”.  It calls for a massive repurposing of resources without actually doing the math on the specifics to be certain it would work (and thank you Stefan for doing the math, good on ya mate!).

    Two more things of the same character:  Renewable Portfolio Standards and Germany’s Energiewende.  Far from slashing carbon emissions, they have locked in fossil fuels (natural gas and lignite respectively).  In the case of RPSs, the forced use of simple-cycle gas turbines instead of combined-cycle plants results in increased net carbon emissions until the “renewables” hit something in excess of 35% capacity factor.  Only the best of the best solar plants appear to get there, so the climate impact of PV is negative (and that doesn’t include methane leakage).

    Meanwhile, almost every such effort is deliberately slanted against nuclear energy to the point that plants with years to go on their licenses are shutting down all over the USA.

    Mark Z. Jacobson is financed by the Precourt Institute, bankrolled by oil baron Jay Precourt.  Obviously he serves the interests of the fossil fuel lobby, and his “Solutions Project” was never intended to be a solution at all.  Can there be any doubt that ALL of these schemes are too?

  27. 27
    Mal Adapted says:

    Raven Onthill:

    “The massive planting of trees worldwide is therefore a project that we should tackle quickly.” Did a “not” get omitted there?

    Well, the next sentence in the OP begins “We should not do that with monocultures but carefully, close to nature and sustainably,” so it appears Stefan is in favor of a “massive” (for some value of the word) tree planting, as one measure among “all of the above”. FWIW, I am too, also for an appropriate value of massive. Among other caveats, I’ll not willingly sacrifice historically non-wooded ecosystems like the North American prairies.

  28. 28

    B 10: Why do people keep taking Nature seriously as a source of science

    BPL: Because it’s the most prestigious peer-reviewed science journal in the world?

  29. 29
    Doug Alder says:

    If the IPCC’s estimate of only 1-12 years remaining in which to reduce by 50% the amount of CO2 we have injected into the atmosphere since the start of the Industrial revolution then there simply isn’t enough time remaining for the trees to mature enough to have reached their maximum carbon sequestration. That’s not to say we shouldn’t do this, we should, but we need faster solutions now.

  30. 30
    Russell says:

    Given how they engineer boreal landscapes, someone should take a serious cracjk at modeling the climate impact of Castor faber as the albedo footprint of each beaver rival or exceed an average human’s.

    On the one hand they are agents of local deforestation, converting boreal trees into dams and fodder, but besides turning relatively dark forest into brighter “beaver meadows, the damming activity the species is famed means every young beaver that builds a new lodge may create a hectare or more of dark pond surface.

    Run the radiative forcing numbers and see what you get, bearing in mind that beavers live about as long as white roofs last, and that the Lawrence Berkley urban albedo methodology equates replacing 16 M2 of black asphalt with white roofing with the removal of 1tonne of CO2 from the atmosphere

  31. 31
    Russell says:

    29.

    “That’s not to say we shouldn’t do this, we should, but we need faster solutions now.”

    One might arrive at faster solutions by reading the IPCC reports more slowly, as they took more than 12 years to write.

  32. 32
  33. 33

    Hi everybody,

    Lively discussion here. I’m one of the co-authors of the paper discussed here. Thanks @stefan for your interest in our research and going through the trouble of fact-checking. I’m chipping in specifically for one statement you made:
    “Therefore, I’d still consider it optimistic to assume that half of the calculated theoretical planting potential can be realized in practice.”

    Why? Because it shows me there is way more agreement between our positions than what appears at first glance. Bear with me:

    When developping future scenarios, it is useful to disentangle the story arc – the scenario per se – from the probability that this story actually unfolds as described.These probabilities keep changing – some variables are slow, others – for example elections in Brazil or the US – are fast. The story arcs have value, irrespectively of their probability of occurrence.

    Among the many possible futures we can imagine, some are going to be way more probable than others. And if the story arc involves a violation of the physical laws of our universe, that probability will actually be 0. If there is no such violation, the probability that such events unfold can be insignificant, but it will not be 0.

    What you are describing are likely story arcs (high probability scenarios) – and we agree with all the points you are making.
    What we outlined with our paper is the extreme limit of what a story arc involving forest restoration can look like – an almost zero probability of occurrence. We measured a potential – and we all know a potential never gets to be fully realized. Beyond that, there no way through.

    We wanted you guys to be aware of this nuance – that has proved difficult to convey in the media. Does it shed a different light on the discussion?

    If you want to find out more about that, you should have a look at this commentary:
    https://www.linkedin.com/pulse/earth-shows-potential-claude-garcia/

    [Response: Thanks for joining the discussion, Claude, and good to hear that you agree with my article! I take your point, and estimating a potential is certainly useful – and I think your paper is a valuable piece of work (apart from the airborne fraction issue). It is like estimating the theoretical potential of renewable energy. I’m not saying your estimate should have been 100 GtC rather than 200 GtC. But it is important to discuss, after such an estimate is published, what additional obstacles there may be that prevent afforestation and that haven’t been taken into account in your estimate.
    In any case my main point here is that the claim by your first author – as quoted by National Geographic – that “reforestation can buy us time to cut our carbon emissions” is the wrong conclusion. We need to cut our carbon emissions right now, and giving politicians the message that in the light of your study we now have more time is dangerous. It was tweeted enthusiastically here in Germany by those that resist emissions reductions. -Stefan]

  34. 34
    MA Rodger says:

    Doug Alder @29,
    There is a hot-off-the-press guest post at CarbonBrief addressing the remaining carbon budget. The number presented is “a remaining carbon budget from 2018 onwards of 580GtCO2 for a 50% chance of keeping warming below 1.5C. This is less than 15 years of global emissions at current rates.” So that would be 580Gt(CO2) = 158Gt(C).
    I’m not entirely sure what “from 2018 onwards” means – whether the 158Gt(C) figure would include 2018 emissions. I’d assume it do because the 2018 emissions numbers aren’t established yet.

  35. 35
    Dan says:

    The carbon sequestation benefit from additional woody cover is not at all clear cut and is not the same as the biomass of the trees. Soil organic carbon is accrued and stabilizes differently along a continuum from herbaceous/grassy communities to shrubby/forested ones. Toward the arid end of the spectrum of where trees can grow, the net impact on carbon sequestration above- and below-ground is negative from the expansion/increase of woody vegetation. As mean annual precipation increases, or aridity decreases, woody vegetation colonizing an area or increasing in dominance can lead to a net increase in carbon sequestration below and above-ground, but even then, that increase is tempered by changes in soil organic carbon storage such that the benefits may not be nearly as large as one would think based on the biomass of the living woody plants, especially in the mid-lattitudes…think the deep dark soils that were under the tallgrass prairies of the central US, which were maintained by fire (and perhaps grazing) but which receive more than enough precipation to support forests (much of the small amount of prairie that isn’t growing corn now is forest already). In contrast soils formed under forests in the central Us don’t hold nearly so much carbon, so while the trees may hold a lot of carbon, the net positive isn’t a huge one.

    It is also worth noting that many elements of biodiversity in the few relatively intact natural communities (e.g. the tallgrass prairies) that remain in areas that could support trees in theory but which don’t due to factors of fire and grazing stretching back to before the industrial revolution and the legacies of those, would be lost…and, in fact, aforestation/woody encroachment are considered to be tremendous threats to biodiversity in such places around the world, ranging from southern Africa to Australia to North America, and the process is the focus of much research. If grazing, cultivation, haying, and the use of fire were stopped in North America tomorrow. A near continuous forest would stretch from central Nebraska all the way to the Atlantic with no need for planting at all.

    A more ecological perspective may be found in this review, though it focuses on mid-latitude systems.
    https://link.springer.com/chapter/10.1007/978-3-319-46709-2_2

  36. 36
    Scott E Strough says:

    Interesting read. Unfortunately it misses the mark in the most fundamental way. Yet again we see good intentions but naively focused on the wrong biome. There is a biome that has been devastated far worse than the planet’s forests. It just so happens this biome is also responsible for cooling the planet.

    https://www.annualreviews.org/doi/abs/10.1146/annurev-earth-050212-124001

    It’s the grasslands. They are in far worse shape. It is a crying shame that many old growth tropical rain forests have been partially deforested. But it is nothing even remotely as bad as the complete destruction of the North American tall grass prairie for example. That is completely gone for all intents and purposes. And more importantly that’s the biome that removes vastly more carbon from the atmosphere, increases albedo, and even lowers water vapor by restoring the hydrological function of soils.

    Sure go plant some trees if you want. But please don’t try and pretend this is to help mitigate AGW. The vast prairies and savannas that were destroyed are what cooled the planet in the first place and put us in our current ice age period. They could do it again. Planting trees to mitigate AGW shows pretty naive fundamental lack of understanding biological functions in regulating atmospheric gasses and cooling the planet.

  37. 37

    ENGINEER-POET said:

    “Mark Z. Jacobson is financed by the Precourt Institute, bankrolled by oil baron Jay Precourt. Obviously he serves the interests of the fossil fuel lobby, and his “Solutions Project” was never intended to be a solution at all. Can there be any doubt that ALL of these schemes are too?”

    Huh? People seem to always forget that conventional crude oil is a rapidly depleting finite & non-renewable resource that has zero future as an energy source, independent of climate change.

    Unless you’re being facetious, which I guess is a form of poetry.

  38. 38
    Al Bundy says:

    Mal Adapted: Among other caveats, I’ll not willingly sacrifice historically non-wooded ecosystems like the North American prairies.

    AB: I’m pondering that, too. Scott Strough and other sources seem to say that grasslands are the absolute best permanent land-based carbon storage ecosystem, especially when measured by water usage. Sure, trees store carbon for a bit, and yes, I advocated here (a year ago?) the use of very heavy wooden construction so as to store the resulting carbon above ground while adding thermal mass and strength to structures. Interestingly, the responses I got were that heavy timber construction is impossible.

    So, which is it? Kill the trees and store the resulting wood productively so as to make room for grasslands, or kill the grasslands to make room for new trees? Or is live and let live where stuff likes to live more ecologically robust?
    _________

    Killian sees insults where none exist:

    “#12, Jan, how about you not be an insulting putz to others?”

    (He non-hypocritically thinks “insulting putz”, “arrogance”, and “pejorative” are friendly greetings?)

    Or am I wrong? Was Jan’s #12 off base? Please, does anybody here support Killian’s take that “I have ever been grateful for the correction!” and

    “I am concerned that the present embrace of Allan Savoury-style non-quantitative holistics amplifies what might be called wishful environmentalism.” are the words of an insulting putz?

  39. 39
    Rtemblay says:

    Restore soil also. Microorganisms in soil can capture a lot of carbon. Life in soil is faster than forest

  40. 40
    Fred Magyar says:

    Just some random thoughts in no particular order.

    As a fan of E.O. Wilson’s concept explained in his book: Half-Earth: Our Planet’s Fight for Life , I think it should be obvious that just planting trees, misses the entire forest…

    Does anyone have any data on how much CO2 might have been sequestered in the recent 9,000 km long sargassum bloom in the Atlantic?

    To me, the elephant in the room is this profoundly misguided collective notion that we must find a way to feed 10 billion plus humans in the next few decades. I think that is a fool’s errand!

    I have a hunch that whether or not we somehow manage to reduce human population in an orderly, equitable and humane manner, this planet’s already severely stressed ecosystems will not be able to continue to support such numbers.

  41. 41

    Paul Pukite wrote:

    Huh? People seem to always forget that conventional crude oil is a rapidly depleting finite & non-renewable resource that has zero future as an energy source, independent of climate change.

    And some people own that resource are banking on being able to sell every last barrel of it before switching to something else.  Jacobson is hardly the first anti-nuclear activist put into business by oil money.  Are you aware that Friends of the Earth was bankrolled by ARCO executive Robert O. Anderson?  Did you know that the original motto of the Sierra Club was “Atoms Not Dams”?

    Are you aware that Hermann Muller, who won a Nobel in 1946 for his work on the effects of radiation on organisms, was financed and overseen by the Rockefeller Foundation?  Try looking this stuff up.

    Are you aware that Muller’s doses and dose rates were extremely high (enough to cause death of many test organisms) and his results simply do not support any valid conclusions about effects (mutations or otherwise) at low doses or rates?

    Muller’s work, fraudulent as it was, was used as the basis of the “linear no-threshold” theory of damage from radiation and rammed through into regulations which pronounced even tiny incremental doses of radiation as dangerous.  Meanwhile, the German medical system pays for people to spend time in radon-heavy mines for the sake of their health.  Somehow they don’t see this as contradicting the push to close all nuclear power plants because of “danger”.

    Unless you’re being facetious

    Nope.  100% serious.  What I have seen, I cannot un-see.  We have been the targets of some massive disinformation campaigns for decades and we are most definitely not the intended beneficiaries thereof.  I hope that you and the others reading this will do some digging and become ones who cannot un-see either.

  42. 42

    I forgot to take that thought to its conclusion:

    Non-solutions like the “Green New Deal” and “planting a trillion trees” are flying thick and fast.  They are superficially (and romantically) attractive but ultimately they won’t do much.  Yet each time one is shown to be unworkable, there seem to be two to take its place in the mind-space.

    Meanwhile, the REAL solution (nuclear energy) which in the 1960’s was forecast to take over from coal, is scarcely mentioned at all.  It remains both rhetorically and legally embattled, with plants shutting down faster than we’re building them.  The impractical and impossible schemes suck all the oxygen out of the room and, with a few exceptions, make it difficult even to compensate those plants for the climate and clean-air benefits they provide so they can stay open.

    Who’s paying for all the news coverage of the unworkable, while quietly working to shut down what actually works?  When the traditional media are going broke that takes money, and it’s got to be coming from somewhere.

    Cui bono?  Only the fossil fuel companies.  Follow the money.

  43. 43
    Scott E Strough says:

    @ 40 Fred Magyar
    I don’t have statistics on that particular bloom, but I do know the marsh grasslands and coastal mangrove forests combined sequester 35 times more carbon than all the oceanic algae blooms combined.

    One interesting thing about Sargasso weed (Sargassum fluitans) in particular though. It is a result of our massive use of biofuels grown in the conventional manner.

    You may not know it but our industrialized factory farming system we developed here in the US has been exported to Brazil. Every year they cut down huge swaths of the rainforest and replace it with cropland, mostly to fuel extreme inefficient factory farming production models where nearly none of the production is actually used for food. Rather the vast majority gets turned into either animal feeds and/or biofuels. Ironically most biofuels made here in the US are sent to Brazil because they use far too many fossil fuels to produce. They don’t meet the standards required by the carbon markets. Then biofuels from Brazil made from grass (usually sugar cane) are sent to the US instead. And also a lot of soy is grown to make bio-diesel.

    Unlike the US though, this is land under forest rather than prairies. Forest soils, especially tropical forest soils, are very thin and poor. They will not support agriculture without massive fertilizer nutrient inputs. These inputs ultimately leach out and down the Amazon river into the ocean where they trigger massive algae blooms.

    So the same agricultural practices causing the algae blooms that decay into dead zones around the US are now showing up as a different sort of algae bloom and now choking the beaches and coastal waters from Africa to the Caribbean.

    https://www.scientificamerican.com/article/ocean-dead-zones/
    https://daily.jstor.org/great-seaweed-invasion/

    And here is a very basic primer as to how a tropical rainforest functions in relation to the carbon cycle.
    http://www.mbgnet.net/sets/rforest/explore/layers.htm

    Notice how different from how a grassland functions in the carbon cycle?

    https://cpb-us-e1.wpmucdn.com/blogs.uoregon.edu/dist/d/3735/files/2013/07/grasslandscooling-nhslkh.pdf

    So it is indeed very very important that we end this very naive practice of making AGW worse by converting natural biomes into agricultural land to grow commodity crops. They do not feed people and they ruin vast ecosystems without benefiting AGW mitigation at all.

    Instead we need the jungle to return in those areas like the Amazon basin, and the prairies to return to the vast areas plowed under for commodity crops like corn and soy.

  44. 44
    Ray Ladbury says:

    Fred Magyar@40: “o me, the elephant in the room is this profoundly misguided collective notion that we must find a way to feed 10 billion plus humans in the next few decades. I think that is a fool’s errand!”

    I only see two alternatives to finding a way to feed them.

    1) Let them starve: In addition to the moral repugnance of this idea, there is the additional downside that this will result in unprecedented environmental degradation over much of the land area of the planet. I certainly hope you don’t advocate this.

    2) Forced sterilization on an unprecedented scale. And I really don’t want to live on a planet where that happens or be part of a species responsible for that.

    At this point it is all but inevitable that these people will be born. Unless we become monsters, we have to try to find a way to care for them.

  45. 45
    Russell says:

    What ever happened to the P. virginatum biofuel plantations that were touted a decade ago?

    They’re not the the stuff of Great Prairies, but switchgrass is tall grass, and its albedo is higher than most trees.

  46. 46
    nigelj says:

    Al Bundy says “Scott Strough and other sources seem to say that grasslands are the absolute best permanent land-based carbon storage ecosystem, especially when measured by water usage. Sure, trees store carbon for a bit, and yes, I advocated here (a year ago?) the use of very heavy wooden construction so as to store the resulting carbon above ground while adding thermal mass and strength to structures. Interestingly, the responses I got were that heavy timber construction is impossible. So, which is it? Kill the trees and store the resulting wood productively so as to make room for grasslands, or kill the grasslands to make room for new trees? Or is live and let live where stuff likes to live more ecologically robust?”

    I’ve wondered this as well. Some big claims have been made that grasslands can store a lot more carbon by using certain types of rotational grazing (Alan Savory) and that crops can store more carbon with regenerative farming techniques and both are better than planting trees. Savory has said “Holistic management as a planned grazing strategy is able to reverse desertification and sequester atmospheric carbon dioxide into soil, reducing atmospheric carbon dioxide levels to pre-industrial levels in a period of forty years.” (Allan Savory, 2014)”

    Scepticalscience did a review some time ago and found that the ability of both croplands and grasslands to store more carbon is rather limited, and would only reduce CO2 emissions by about 5% and this is way below Alan Savorus claims, because this is what published research of field trials showed on balance, and you have the problem that higher temperatures will cause soils to become a net carbon source eventually.

    https://skepticalscience.com/print.php?n=4412

    This point of view was contested by people in a later article (sorry cant find this) claiming the research was out of date, and some root fungus pathway involving glomalin can be stimulated to conserve a lot more soil carbon if the right forms of rotational grazing are used. But the matter was never really resolved convincingly to me, although I suspect the answer is somewhere between what the pessimists and optimists think. But I like to have some precision on whats realistic.

    Could realclimate do a review of this soil carbon issue in a similar way to the trees issue?

    Clearly AL Bundy could be right some of the answer may be ecological zones. Sloping land tends to suit trees more than crops etcetera. I also think that we obviously need a certain proportion of land for crops anyway, and its hard for me to see the whole world becoming vegetarian anytime soon so a large proportion of the world will still be in grasslands, so it would make sense to 1) farm crops in a regenerative way that conserves soil carbon and 2) graze cattle in a way that conserves soil carbon. But this doesn’t answer the fundamental question of which is better at storing carbon, is it trees or crops or grazing and what can each potentially store as a proportion of emissions or something like this?

  47. 47
    nigelj says:

    https://www.vice.com/en_us/article/7xgymg/planting-billions-of-trees-isnt-going-to-stop-climate-change

    “Planting ‘Billions of Trees’ Isn’t Going to Stop Climate Change” Some interesting perspectives from various scientists and interest groups.

  48. 48
    nigelj says:

    Ray ladbury @44 I agree options 1 and 2 are totally repugnant, but there is a third option of reducing population size by just promoting use of contraception and the wisdom of having smaller families, better education of women and promotion of womens rights, and better healthcare and pension systems which makes smaller families attractive. This could make a surprising difference to population size. Even a fertility rate of 1.5 achieved over the next two decades would stop population reaching 10 billion people. Challenging to achieve but far from impossible.

  49. 49

    Ray Ladbury wrote:

    I only see two alternatives to finding a way to feed them.

    1) Let them starve: In addition to the moral repugnance of this idea, there is the additional downside that this will result in unprecedented environmental degradation over much of the land area of the planet. I certainly hope you don’t advocate this.

    2) Forced sterilization on an unprecedented scale. And I really don’t want to live on a planet where that happens or be part of a species responsible for that.

    At this point it is all but inevitable that these people will be born. Unless we become monsters, we have to try to find a way to care for them.

    Right now we ARE feeding them; Africa receives truly massive amounts of food aid from Europe, Australia and the Americas.

    This situation is not sustainable, especially if Africans flood out of Africa and consume the surpluses at their source.  Any kind of major crisis (energy, fiscal, social) in the West which affects grain production is going to hit exports first and hardest.  AAMOF, we’ve already seen this; the 2010 Arab Spring riots were sparked by high food prices driven in part by refusal of the US EPA to decrease fuel ethanol blending levels in the face of lower harvests.  (Yes, the Obama administration LITERALLY decided to feed US SUVs instead of people on the continent of Africa.  US livestock farmers were also demanding more grain be allocated to them.  They were refused.)

    Since the current African population explosion cannot be fed indefinitely, it won’t be.  The choices we have are how it will end:

    1.) Voluntary action by Africans to stop their unsustainable population growth.
    2.) Involuntary birth control imposed by e.g. lacing food aid with contraceptives.
    3.) Collapse of the aid system and mass starvation.  (Sooner is better; fewer to starve.)

    We already know they won’t do #1.  #3 is what you’re trying to prevent.  #2 is all that’s left.

    There once was a guy whose Usnet signature was “Are humans smarter than yeast?”  The answer for at least some segments thereof is “definitely not”.

  50. 50
    David B. Benson says:

    So You Think We Are Reducing Fossil Fuel? — Think Again
    James Conca
    2019 Jul 20
    Forbes

    https://www.forbes.com/sites/jamesconca/2019/07/20/so-you-think-were-reducing-fossil-fuel-think-again/#4846e2d352fb

    So while doing what we can to eliminate fossil fuels we need to also be planting trillions of trees.

    http://bravenewclimate.proboards.com/thread/694/trillions-trees
    For further links to related posts.