How trees could save the climate

ETH Zurich

IMAGE: Figure A shows the total land available that can support trees across the globe (total of current forested areas and forest cover potential available for restoration. Credit: ETH Zurich / Crowther Lab

IMAGE: Figure A shows the total land available that can support trees across the globe (total of current forested areas and forest cover potential available for restoration. Credit: ETH Zurich / Crowther Lab

The Crowther Lab at ETH Zurich investigates nature-based solutions to climate change. In their latest study the researchers showed for the first time where in the world new trees could grow and how much carbon they would store. Study lead author and postdoc at the Crowther Lab Jean-François Bastin explains: “One aspect was of particular importance to us as we did the calculations: we ex-cluded cities or agricultural areas from the total restoration potential as these areas are needed for hu-man life.”

Reforest an area the size of the USA

The researchers calculated that under the current climate conditions, Earth’s land could support 4.4 billion hectares of continuous tree cover. That is 1.6 billion more than the currently existing 2.8 billion hectares. Of these 1.6 billion hectares, 0.9 billion hectares fulfill the criterion of not being used by hu-mans. This means that there is currently an area of the size of the US available for tree restoration. Once mature, these new forests could store 205 billion tonnes of carbon: about two thirds of the 300 billion tonnes of carbon that has been released into the atmosphere as a result of human activity since the Industrial Revolution.

According to Prof. Thomas Crowther, co-author of the study and founder of the Crowther Lab at ETH Zurich: “We all knew that restoring forests could play a part in tackling climate change, but we didn’t really know how big the impact would be. Our study shows clearly that forest restoration is the best climate change solution available today. But we must act quickly, as new forests will take decades to mature and achieve their full potential as a source of natural carbon storage.”

Russia best suited for reforestation

The study also shows which parts of the world are most suited to forest restoration. The greatest po-tential can be found in just six countries: Russia (151 million hectares); the US (103 million hectares); Canada (78.4 million hectares); Australia (58 million hectares); Brazil (49.7 million hectares); and China (40.2 million hectares).

Many current climate models are wrong in expecting climate change to increase global tree cover, the study warns. It finds that there is likely to be an increase in the area of northern boreal forests in re-gions such as Siberia, but tree cover there averages only 30 to 40 percent. These gains would be out-weighed by the losses suffered in dense tropical forests, which typically have 90 to 100 percent tree cover.

Look at Trees!

A tool on the Crowther Lab website enables users to look at any point on the globe, and find out how many trees could grow there and how much carbon they would store. It also offers lists of for-est restoration organisations. The Crowther Lab will also be present at this year’s Scientifica (web-site available in German only) to show the new tool to visitors.

The Crowther Lab uses nature as a solution to: 1) better allocate resources – identifying those re-gions which, if restored appropriately, could have the biggest climate impact; 2) set realistic goals – with measurable targets to maximise the impact of restoration projects; and 3) monitor progress – to evaluate whether targets are being achieved over time, and take corrective action if necessary.

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Reference:

Bastin JF, Finegold Y, Garcia C, Mollicone D, Rezende M, Routh D, Zohner CM, Crowther TW: The global tree restoration potential, Science, 5 July 2019, doi: 10.1126/science.aax0848

From EurekAlert!

67 thoughts on “How trees could save the climate

  1. Yes, but. Once the forest reaches its maturity climax and attains its maximum biomass it won’t capture any more net carbon dioxide. In New Zealand that’s in about 30 to 60 years for Pinus radiata, the major plantation forestry tree and the species being planted most by the current government’s “1 billion trees programme”. After maturity is reached, as much CO2 is released through respiration, reproduction and decomposition as is captured and converted into biomass.
    So this is a temporary fix, if a fix is needed at all. After all, plants do best at 2000+ ppm CO2, and they are performing sub-optimally at the present 400+ ppm level. Another objection is that many plantation forests (and many indigenous ones) are subject to destructive events such as fire, disease/pests and human utilisation, which will release all that expensively sequestered CO2 back into the atmosphere.

    • The solution is to turn the trees into charcoal, which on average takes about 1300 years to decompose. If you add the charcoal as a soil amendment then all the microorganisms that are supported by the charcoal will also take CO2 out of the air for some period of time. So converting trees to charcoal for soil amendment changes the time scales from near term to very long term.

        • I’m surprised that the quoted figure is so short.
          However, I’m more sure that they simply don’t know, and that the figure is also enormously context dependent. Just think about how all those stonking enormous coal deposits came to be formed in the first place.

      • Or harvest the mature trees at maturity and “sink” their carbon in old open pit coal mines covered by water to prevent immediate decomposition. Once the pit is full, cover it over with marshy peat moss and let nature take it’s course. Then replant the harvested trees and start the process over again. Eventually you will have a new coal bed with a peat bed on top of it.

    • EGGZACTLY!!!
      Not to mention the fact that atmospheric CO2 has ZERO to do with the weather, and as a constituent of the atmosphere its level is determined by Hook’s Law.

    • Along the same lines, one problem with forestation is that it decreases the albedo of the Earth’s surface. I understand that is one of the feedback effects from increasing CO2 – it encourages greening of desert areas, which impacts climate in two ways:
      – sand has much higher albedo that forest (just look at the Sahara vs Amazon in the blue marble images) so more heat is retained by a forest, and
      – trees release water vapour, which is of course a much stronger GHG than CO2
      My guess is that increasing forested areas is more likely to increase than decrease the average temperature.
      On a related topic, in North America (at least) our forest volume has been rising at least in part because we have been aggressively extinguishing forest fires. Those fires can be delayed but not avoided (except perhaps by aggressive harvesting of forests and conversion into charcoal as another commenter mentioned) so there is today a “CO2 debt” from unburned trees.

      • so there is today a “CO2 debt” from unburned trees.

        But the amount of unburned “forest” trees might be smaller than the amount of unburned “homes, businesses and furniture” trees (lumber). A lot of CO2 is sequestered in wood products.

    • Temporary yes, but 200 GT of carbon sequestration would 100% offset about 20 years of CO2 emissions from fossil fuels.

      Not bad if your goal in life is to waste as much life-giving CO2 as you can.

      I’d much rather see that carbon be used to eliminate degraded global soil. There isn’t enough “surplus” CO2 to do that, so the last thing we want to do is waste it on a massive global tree growing exercise.

      http://www.fao.org/3/u8480e/U8480E3z.jpg

      Here’s a car better use of surplus CO2:

      https://www.businesswire.com/news/home/20190612005271/en/Indigo-Launches-Terraton-Initiative%E2%84%A2-Remove-Trillion-Tons

    • Using Occam’s Razor: tree lined streets are cooler than tree-less streets; forest or woods are cooler than open fields; tree shade is cooler than standing in direct sunlight. The difference between sun and shade is so significant it is easily perceivable just using our physical senses without the need for sensitive equipment measuring fractions of a degree. In addition forest holds more moisture than open land which is also easily sensed just by touching the ground in each. It is already established knowledge (but perhaps ignored) that deforestation will open up the ground to direct sunlight. The open land will heat up and heat up further as the moisture contained is evaporated. Add in water extraction so the water table drops and heating will continue as there is no evaporation to provide any cooling.
      Fixating on removing CO2 from the atmosphere to cool the planet is a distraction from other more obvious reasons that the Earth’s surface is warming. If you drove a car with an empty or less than full radiator the engine will over heat, period. If you drove a car with a full radiator but were stationary in traffic the engine will overheat because there is no air to take away the heat, period. If we cut down vast tracks of tropical forests AND remove ground water AND have settled weather, the land will overheat, period. Is that happening anywhere?

      • hi Stephen, I’m not sure Occam is a help here, but I will say (with reference to my comments above) that I went through a similar cycle of analysis to you. Here are some resulting insights:
        – Ambient heat is time-of-day specific: the open field feels hotter in the day, but cooler in the evening, night, and early morning.
        – Compare apples to apples: taking a walk above the tree tops might feel no cooler than a walk above the open field.
        – While walking in the desert, our bodies feel heat from both down-welling and reflected light. If we weren’t standing there, the reflected light would be radiated out to space, thus not contributing heat. so the fact that we feel hotter might be an indication that in the natural state, the heat is being reflected away rather than absorbed by the vegetation.
        And don’t get me wrong – I really love the forest. I just wish I felt more confident that forests contribute less heating than deserts.

        • boffin77 July 5, 2019 at 3:24 pm
          ” I just wish I felt more confident that forests contribute less heating than deserts.”
          They must do because all record temperatures are in deserts and not forests or jungles and we measure temperatures at or near the surface, with the exception of oceans.

        • “– Compare apples to apples: taking a walk above the tree tops might feel no cooler than a walk above the open field.”
          I understand the point you are making but glider pilots avoid flying over woods, forests, lakes and wetlands because there is little to no heat coming off these, except for a short period in the evening when the trees and water are momentarily warmer than surrounding land. In addition being downwind of open dry land or roads or buildings is noticeably warmer compared to being downwind of woods and lakes.

        • boffin77 – July 5, 2019 at 3:24 pm

          taking a walk above the tree tops might feel no cooler than a walk above the open field.

          Well “DUH”, the heat that you might feel is because your body is absorbing the solar irradiance.

        • Stephen, thanks for the interesting points. All worth contemplating.
          WRT to the photo of London, keep in mind that temperature of the sunlit ground is usually more strongly influenced by heat capacity than by the amount of heat absorbed. The water you mention has absorbed close to 100% of the energy of the light shining on it, but water has a huge heat capacity so it remains cool. Similarly wet soil heats up more slowly than dry soil even when it absorbs the same amount of heat/light energy. Specific to our discussion: if the vegetation looks dark from above, in the visible bands, then it is absorbing more light. If, in the visible bands, concrete looks brighter than grass, then the concrete is reflecting more and absorbing less visible light. The concrete feels hotter than the grass because it has a) poor heat conductance, and b) low heat capacity.
          Nonetheless: yay grass.

  2. Erm, quite. Only a temporary store at best. And is it carbon or carbon dioxide we are, sorry, they are interested in?

    • Trees pull CO2 out of the air and sequester the carbon atoms in their biomass.

      Photosynthesis is the first step, but there multiple steps that lead to carbon in tree biomass coming from atmospheric CO2.

      • Yes, trees are an awesome carbon capture solution: efficient (very high surface area), self-replicating, and they adapt to higher CO2 by growing faster.
        The problem as noted by Coeur de Lion is that they tend to rot or burn, releasing the carbon back into the air after less than a century (at least for the non-old-growth coniferous forests). Nonetheless, they may represent a promising first step in a future carbon sequestration solution.

  3. All that of course is if you accept the fact that CO2 is bad. There seems to be considerable evidence that it does not lead or cause (much at least) climate change and that CO2 is historically very low.

  4. If a 30 – 60 year fix that puts more trees in the ground and provides cover for animals, birds, insects and other forms of life will stop the whining until the whole hoax is exposed, I say lets plant trees.

  5. Of all the geoengineering schemes it is by far the best, except for the fact that it would be nearly impossible to accomplish on any kind of grand scale, let alone what they are talking about, and would be hugely expensive. Now, growing more trees could certainly have benefits, but removing CO2 from the atmosphere is not one of them.

    • The Prairie Farm Rehabilitation Act provided trees for shelterbelts, surface water storage, etc to help western Canadian land recover from the extreme weather of the 1930s. Shelterbelts slowed down surface wind and erosion, caught drifting snow, provided firewood, on a grand scale. Modern zero tillage farming now in use mimics nature and continues to rebuild those once eroded soils. Trees are generally a good thing to have around, where the climate permits. Coastal cedars or walnut can live hundreds of years, even the odd elm or burr oak in Alberta’s extreme prairie climate can go a century before being made into shipping pallets. If you change our minds in 60 years you can burn them.

  6. I thought trees were already helping the climate by being burned in Biomass power stations, e.g. Drax in England.

    • Ian,
      Well said.
      Bureaucrats in Brussels will be upset for making fun of their CO2 and RE fantasy, which implies if it is biomass burn it. It won’t hurt, because it is renewable.
      They do not care about the other fauna and flora damaged by all that tree cutting.

  7. The problem is that the climate change we are experiencing is caused by the sun and the oceans over which mankind has no control. Despite the hype, there is not real evidence that CO2 has any effect on climate and there is plenty of scientific rationale to support the idea that the climate sensitivity of CO2 is zero. There may be many good reasons for having more trees but affecting climate is not one of them.

  8. Planting trees would be the least of the harms caused by climate madness. If we bury that CO2 by collecting it and sequestering it deep underground, especially if we get no additional benefit like enhanced oil recovery, then it is lost back to the deep earth for a very long time, and the effort is wasted if it doesn’t have a secondary benefit. However, if it is trees/forests, they have all kinds of utility for the planet as we all know which is a long list. And the forest will be available to go back to CO2 in the atmosphere in the future, which it most surely will except for what we sequester more longer term like lumber products. I believe the long term future of the planet will be indebted to higher CO2 concentration, making things much better on balance. It is happening already as we se in the overall greening of the good Earth.

    Whatever we wind up doing with the spending of monies to ‘tackle climate change’ we should try and steer the funding and spending on things we are going to need anyway, such as a hardened electrical grid with more capacity since that is the long term future which will be hard to improve on. Spending some money on creating forests isn’t dead money, especially if we set up with no direct cash subsidy, and let it create its own privatized market for long term lumber/forest products. There is no harm in doing so, and if this would shut up the daily stupidity coming out of the ‘climate cartel’, then this would be a good start. I have been doing this for 40 years and have millions of trees growing, much of it on my own private lands. I would invest more heavily in this if I was guaranteed not to be taxed into oblivion with ridiculous schemes of property taxation and idle wealth taxation, amongst other insane red tape beuracratic regulations.

  9. What’s funny is, this stuff is embraced by the loonies at The Guardian but when this was suggested a few years ago in Australia by the then PM, Tony “the evil right wing nutjob” Abbott, the same people said it was rubbish. As usual with the left, it’s not the cause, but the side.

    • While reading this article I had the same thoughts about the maligned Abbott solution of planting millions more trees across Australia.

      At the time I didn’t think it would make any difference to the climate but was still a great idea to increase inland rainfall, provide habitat for various flora and fauna, etc.

      However, the plan was rubbished by the Greens and the left as it apparently didn’t try to immediately stop society’s release of “carbon pollution”, whatever that is.

      It’s similar to the silence about the planet becoming about 12% more green over the past half century. The only rational explanation I can think of is that the Greens don’t like green.

      • There are at least fifty shades of green, and the Greens don’t like 49 of them. There is only one “true green”, and that’s red.

  10. “…Many current climate models are wrong in expecting climate change to increase global tree cover, the study warns…”

    Say it isn’t so. Climate models are wrong?

  11. I love trees, especially as a amateur photographer, they are beautiful to look
    at, and in our hot climate they provide much needed shade. The cows and
    sheep and many other creatures love them too.

    But lets stop this nonsense over CO2. Its a good gas and we need lots more

    MJE VK5ELL .

  12. The issue I see is .. what about all the windmills and solar panels?
    They’re already cutting down forests to pave the way for wind & solar.
    Are the greens going to fight over this land?

  13. Not the craziest idea I’ve heard lately, that award goes to Arizona U. Watch as the oh so seriously-voiced BBC presenter outlines the problem over stock footage of cooling towers (yes, that’s WATER VAPOUR folks!) then changes his tone to optimistic as he reveals the solution.. ‘artificial’ trees! When you have recovered from your fit of uncontrollable mirth, discover what we are going to do with our captured CO2. We can add it to concrete and use it as a building material! Clearly the BBC has no idea how much CO2 is emitted by cement production.

    • I always chuckle at the irony, when misleading videos show clouds of steam and call it CO2. Truth is, steam is a much more powerful greenhouse gas that CO2, so if they told the truth they could still mention greenhouses.
      Of course water vapour rapidly returns to earth as rain, which would undermine even that argument.

  14. ..and in other news

    scientists discover when you chop down a bunch of trees..
    …CO2 levels rise

    …film at 11

  15. I took a look at their website. Living and working in the boreal forest of Canada, I was a bit taken aback by the high “forest restoration potential” of areas that I’ve walked through, driven through (when there were roads) and flown over in the last 40-odd years. Fact is, the areas where they have low “forest cover” and high “forest restoration potential” are mostly lakes, or swamps, or peat bogs, or occasionally areas of bare rock. None of which have any forest restoration potential whatsoever.

    Clear-cutting is the favoured forestry approach in the boreal forest which has mostly a mixture of pines, spruce, fir, birch and aspen, usually trees that aren’t that big, so cutting has to be done on a large scale to be profitable. About 50 percent of clear-cuts are replanted with the fastest-growing evergreen (jackpine), and half are left to re-vegetate naturally (which they do quite fast). The notion that there are large areas of northern Canada that have had been humanly deforested is simply nonsense. Letting the forest grow back as quickly as possible ensures future business for the forestry companies, who do know a little about the land where they operate.

    It would not surprise me if my criticism applied equally to Siberia, but I don’t have much local knowledge there.

    OK, the clay belts of Ontario and Québec were mostly cleared for farming at times between 1880 and 1940, but the farming was marginal subsistence farming over most of the areas, and farms have been widely abandoned – the forest is coming back by itself over most of the clay belts.

    Farmland in southern Canada and the prairies is valuable and it feeds us, so while it may have “forest restoration potential” it’s hard to see farmers giving up farming to plant trees. And what would we eat then? Most of the Canadian prairies were never forested anyway. They were grassland.

    As for Europe, parts of which I know well, it’s mostly either cities, farmland, or existing forest. Not much potential for reforestation there unless they give up farming.

    It’s so easy to grab loads and loads of satellite data, run some computer analysis and reach conclusions, but it would certainly be better if they had actually studied airphotos, or maps, or high-res satellite images before they published this. They might have then thought that genuinely deforested areas (as opposed to swamps, lakes etc.) have been deforested for a reason, and that reason is overwhelmingly – farming. Do they suppose that people cut down trees for fun, and do they suppose that abandoned land won’t revegetate itself naturally? Shallow and simplistic are words that come to mind.

    If their reforestation proposals were accompanied by population reduction, they would make more sense, but we won’t go into that part of the great greening.

    Parts of the Middle East could be an exception to my carping. Mostly deforested by over-grazing by goats in historic times, there is real potential for reforestation. Look at Israel, where they actually do reforestation.

    Or large parts of Africa, where people (mostly women) cut trees every day to cook over open fires. Just give them rural electric service, or propane delivery services, and proper stoves to cook on (how often have we heard this refrain here?). The forests would come back without much outside help. And the health benefits……. well, you know already.

    • This sounds like a bunch of nonsense.

      “Increasing the carbon levels in agricultural soils from today’s levels of approximately 1% back to native levels of nearly 3% would sequester the same one trillion tons of carbon dioxide from the atmosphere.”

  16. Ditto Smart Rock. Vast areas shown as potential forest are currently occupied by native vegetation and it’s not forest. No wonder the authors were surprised. The analysis has very low validity.

  17. why are we talking about carbon sequestration again? Haven’t we established this is not cause but effect of the natural climate cycle?
    Above “research” doesn’t pass pub test; there are no (known to me) evidence of reduction in tree coverage in equatorial areas with warming and CO2 fertilization; contrary is true https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth
    But even we assume for a moment there is such thing – amount of land in Northern Hemisphere exceeds that in equatorial areas, right?

  18. Would reforestation in most parts of the earth have any chance of staying ahead of forest clearing for wind farms, solar farms, and biofuel plantations?

  19. Al Gore is Doctor Honoris Causa of EPFL, the sistership of ETHZ.

    In 2009, Mr. Guy Negre, a famous con artist hacked the system and obtained scientific endorsement by
    EPFL for his green of the greenest air powered cars. Political personalities, scientists, all pressed to be on the photos that day.

    Both technological institutes are federally funded and regularly cited as justification for political maneuvers towards green energy, clean tech, 5$ per liter of gas and alike planned cost of living increases.

    Now, after loosing quite some feathers in the process, both schools desperately attempt to rebuild a new credibility.

  20. I was once willing to go along with this sort of “initiative” since planting trees provides work as well as other benefits. As someone who was once responsible for derelict land reclamation I guess I can claim to have planted upwards of 2 million trees. Looking at the sites on Google Earth, they seem to have matured.
    One of my sons used to work for Green Corps here in Australia, and their standard was 400 trees per person per day. There are several problems. Greenies and climate alarmists don’t plant trees. 6 and a photo opportunity is all that you can expect. Plus they would do it wrong. Its hard work, so mostly they They just want to sequester the treed environments that exist, keep ordinary humans out, or engage in genocide as per WWF and the Baka people of Cameroon. Here, if the natural forests are locked up you get catastrophic fires, or they become havens for ferals, both human and animal. Somebody just got grant money for sitting at a computer and looking at Google Earth.

  21. The greening is already happening, NASA says the Earth is 8% greener than in 1980. Nature has a way of taking care of itself.

    https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth

    Satellites show that global forests have grown in size by 9%.

    https://www.sciencemag.org/news/2017/05/earths-forests-grew-9-new-satellite-survey

    The Earth has trillions more trees than first thought. There is something like 280 trees for every single person on the planet.

    https://www.bostonglobe.com/ideas/2015/09/02/surprise-the-earth-has-trillions-more-trees-than-thought/2C0o8JJKqdGn6MAzsf3AOI/story.html

    Forests have higher density than thought.

    https://www.nature.com/news/global-count-reaches-3-trillion-trees-1.18287

    Older trees are growing more quickly due to climate change.

    https://wattsupwiththat.com/2019/05/09/climate-change-is-helping-older-trees-grow-better/

    Red Spruce growing 106% more quickly due to higher levels of CO2.

    https://climatechangedispatch.com/red-spruce-growth-co2/

    NASA, global greening in India and China.

    https://earthobservatory.nasa.gov/images/144540/china-and-india-lead-the-way-in-greening?utm_source=CCNet+Newsletter&utm_campaign=77eb1ef5ff-EMAIL_CAMPAIGN_2019_02_13_10_44&utm_medium=email&utm_term=0_fe4b2f45ef-77eb1ef5ff-36435781

  22. Interesting point of view and I hope they have thought of wildfire risk. And i wonder why there are no trees in these areas as in most tree supporting areas forest is the natural cover. Europe without humans would be one big forest and this is the case in most habitats. Change of land use in this dimension might also have an impact on albedo, and several other qualities with an effect on climate. Quite the contrary of the suggestion to reduce forest cover in Siberia to save the permafrost though.

  23. It’s a very good thing to do, but won’t be fast enough to avoid a few key thresholds.

    So, let’s do this asap, but nothing changes in terms of transitioning speed required to move from oi&gas to non carbon based energy sources.
    We still need to drop fossil fuel and adopt nuclear/s/biofuels etc etc.

    Then again, with a retarded moron in the White House and a criminal GOP Senate … there is little hope, the USA will lead this $5Ts business development opportunity …

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