Forests help cool the planet

Written by tim


Climate change can be counterintuitive. For example, one way to cool the planet would be to clear cut the entire Northern hemisphere. Trees are dark, and absorb heat much more strongly than snow, which reflects light very well. By replacing large swaths of the planet’s dark surfaces (the boreal forest) with light ones (snow and rock), we could pretty significantly reduce the global temperature.

This principle also works in reverse. We can take bright surfaces that cool, such as deserts, and replace them with darker ones, such as forests or crops, increasing the global average temperature.

Here’s an interesting example: in biblical times, the region around modern Lebanon, Israel, and the Palestinian Territories was forested. Following orders (Joshua 17:15), the Israelites went “up into the forest country and clear[ed] an area” for themselves. The result was a drop in the local surface temperature, as bright desert replaced dark forests, and also an increase in the global concentration of greenhouse gases, as those trees released tons of carbon dioxide.

In 1964, the Yatir Forest was planted by the Jewish National Fund, returning some 30 square kilometers to the original ecosystem. A new study shows that although the local temperature around the Yatir Forest has increased as a result, the forest has also absorbed a significant amount of carbon, about 5 tons per acre. That’s nearly as much carbon as forests with similar species in other parts of the globe, and a surprisingly large amount considering the extreme dryness and heat that defines the desert. It also means that the increase in local surface temperature is offset by the decrease in atmospheric carbon!

I have often insisted that the correct framing of the climate change is that we have a greenhouse gas problem, not a temperature problem (though they’re obviously related). When we approach climate change through the lens of global average temperature, we run the risk of implementing strategies like clear cutting forests to reflect sunlight and recreating volcanic eruptions to cool the planet. How about some better solutions, like reducing our carbon output and replanting native ecosystems to absorb the carbon already in the atmosphere? Which sounds better to you?

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  1. michael

    I was almost ready to fire a “what were you thinking reply.” Your last paragraph wrapped up nicely I think.
    Free association is a two word phrase that we should all become familiar with. Earth’s systems freely associate with one another in ways that are unpredictable. The carbon cycle is an integral part of that free association. Cutting trees to relieve temperature in one place may have drastic consequences in another.

  2. a concerned American

    Folks, I have a very hard time trusting this information here. It makes me think you are on the wrong side of the street. I am going to unsubscribe and wanted to let you know. As far as adjusting the balance of gases on the planet, what better way than to plant *more* trees? Yes of course let’s encourage native plants, and of course dark colors absorb heat. But shade also cools an area, true? What of the urban island heating effect in cities where pavement is exposed to the sun, and trees help shade it and thus cool the area down? It might be best to replace dark-colored roof tiles with lighter ones and the like, but not to cut down trees and entire forests. Sorry, sounds to me like you guys have been bought off and you are counting on your readers not thinking. Wrong assumption, and what an insult to our collective intelligence! I am going to unsubscribe and pass word along.

  3. Tim

    It seems to me that we agree about planting trees as a good thing. Perhaps “a concerned American” didn’t get to the final paragraph?

  4. Anonymous

    PS Historically, wherever Man has interfered with nature, things have gone wrong. Think about it. Every time. To shave off trees from forested areas, and to plant the deserts, may be asking for more natural backlash. Think about it. Nature has a wisdom to it, and it is because of Man’s arrogant assumption that we know better, that we are all-capable, and that there are no limits to what can be done, that we are in the situation we are now. Think about it. And, consider what you say and the moral responsibility you have before you say such words. The entire globe could expire because of this matter, and you are treating it like frivolous play and breezy-easy thought. Well, think harder, not breezier and easier.

  5. michael

    I don’t think tim believes removing trees is a solution…he wrote that in his last paragraph. He simply offered, I think, that there are some folks who might, with narrow thinking, remove trees to reduce temperatures.
    He suggests planting trees and removing carbon…even though in the form of a question to all.

  6. michael

    Curiously, the last paragraph is fairly lower than the previous four…perhaps it is being missed???

  7. Tim

    Thanks, michael!
    I am certainly not trying to advocate for deforestation as a solution to global warming.
    The albedo effect is an important consideration in land-use decisions, which is why we should have more tree cover than asphalt as the anonymous commenter above says. My greater point is that if we narrow our consideration of climate change to just “global warming,” then awful ideas like increasing the albedo of the planet by cutting trees down seems like a plausible solution.
    What we have, though, is a greenhouse gas problem of which one symptom is increasing global average temperature. That’s the cause behind the symptom, and I’m intent on treating the cause.

  8. Anonymous

    Tim, I do understand the last paragraph and of course, the point is well-taken. I fault our mainstream education for misleading us to think that isolated chemicals are the whole issue. They are not. Chemicals all work together in the context of a greater whole, offsetting and balancing each other’s functions. Some may be acidic, others neutral, others alkaline, etc and one cannot function healthfully without the other. You get the point.
    YOur statement is based on the mainstream educational thought that carbon is the sole consideration here. However, to deforest those forested areas and plant the barren deserts may be making some serious environmental mistakes. It is considering the isolated chemical matter, not the whole context, as before. Again this is the way we as a society are taught to think, and it is a big mistake. That’s my two cents worth and my heads up.

  9. Anonymous

    Tim, perhaps the context and the way it is written *sounds* like you are advocating for deforestation. It can be so hard to understand peoples’ intents behind writing sometimes, can’t it, when in truth the writer is thinking something very different than the way it came across in print. It *did* sound like you are advocating for deforestation. If I misunderstood the intent, my apologies but please accept this feedback as an editorial note, for the future. Being facetious or writing ironies can be very confusing to the reader, unless clearly stated as such.

  10. gatcheson

    and putting the paragraph with the critical turning point below a big image break apparently means a lot of people miss the whole point.

  11. Garrett

    While I agree with the overall point of your article, you lost me with your use of examples. Are we now citing biblical quotes as historic fact? In what years did this cutting take place, what area of forest was cut down, and where is the evidence that there was a drop in local air temperature and an increase in the global concentration of greenhouse gases? In “biblical times” that increase would have been insignificant. Using biblical references in what should be rational discourse on what is happening to our environment should be avoided, especially since the typical conservative, anti-environmental type is likely to use the same tactic and probably has many contrary examples (perhaps the one where man has been granted dominion over land and beast).

  12. Dan

    Internationally, there is support for preserving forests through payments to countries that protect them. This is through a program called Reducing Emissions from Deforestation and Degradation (REDD). Nationally, in the US, legislation in Congress would affect how REDD operates. How this

  13. Jonno

    Haha I find it hilarious that people aren’t reading to the end… And that there is a big discussion/argument because of it. 🙂

  14. Kevin Spelts

    This experiment was conducted in a semi-arid landscape and the finding that these semi-arid forests and landscape can absorb as much (if not more) CO2 as forests in humid landscape is truly exciting news.
    Too, these results might not necessarily be applicable in all landscapes (humid mountainous forests versus semi-arid woodlands)–apparently the Yatir forest cools not necessarily or exclusively by evapotranspiration but by “air cooling” where heat is transferred from the leaves directly to the (advecting) air blowing through the forest. This too is exciting news as well.
    As for the albedo versus CO2 effects of afforestation–it appears that after a few 10s of years, there is a net cooling effect from CO2 sequestration (even in the presence of decreased albedo induced warming).
    If this is true, and I have no reason to doubt that it is, it seems that simply increasing albedo via deforestation at the expense of other ecosystem services (e.g., carbon sequestration) seems to ignore the potential consequences of our actions over longer time periods.

  15. Dan

    Liked your to-the-point comments. Are you familiar with the Reducing Emissions from Deforestation and Degradation (REDD and REDD+) proposed internationally and included in the Copenhagen Accord. There may be possible opportunities for desert-like areas wuth sufficient water (!) for afforestation. What do you think? What is your affiliation? I am recently retired from the Economics Dept at Humboldt State University. More of my background is at my blog
    (see my earlier question as yet unanswered)

  16. Kevin Spelts

    Greetings Dan:
    I am only vaguely familiar with REDD although I have been following the hyperlinks you listed–thank you.
    Afforestation has and is likely occurring in many landscapes of the American West (for ex., and ).
    Apparently the expansion and contraction of these types of forests have occurred in the past. Some workers have opined that wetter weather in the 1920s in parts of America may have accelerated Juniper expansion.
    However, it appears that Juniper expansion into sagebrush steppe landscapes are associated, in some instances, with increased runoff and erosion (see )–these types of consequences should be considered when afforestation of semi arid landscapes are considered.
    Thus, I don’t know how successful intentional afforestation of semi-arid landscapes would be. Certainly, one of the largest hand planted forests belonging to the USFS is located in and near the Sand Hills Ecoregion of Nebraska. Apparently this forest began as an experiment that began in the early 1900s.
    As you probably know, climate change is affected by many agents to include quasi-periodic (volcanism), periodic (ENSO, PDO, AMO), orbital (Milankovitch theory), solar (increased production of condensation nuclei from increased galactic cosmic rays during periods of low solar activity), land use land cover changes (Adegoke and Pielke–these types of land use changes probably deserve greater consideration by the climate change community) as well as radiative forcing from greenhouse gases.
    It appears that we can affect the emission of human produced greenhouse gases and land cover changes.
    Thus, if our only goal was to sequester carbon, and the results from the Yatir Forest are transferable to other semi arid landscapes, then I suppose intentional afforestation of semi arid landscapes could be a means to sequester carbon. However, there are other competing goals and forcings we should consider.
    I have many affiliations; I try to walk the middle path based on scientifically defensible research shared with and used by various stakeholders. I try to explain highly technical matter to interested parties–I aspire to explain things like Carl Sagan often did.

  17. michael

    Every forest ecosystem evolved thru succession. In the end, a stable forest ecosystem is defined by a climax specie. We will do ourselves a favor by understanding how and why a particular species became dominant and sustainable.

  18. Kevin Spelts

    I agree that we find late successional or climax species in many landscapes under current climate conditions.
    However, if we perturb the climate, what was once a hemlock forest under early Holocene conditions is now a landscape where the forest is covered by sequences of aeolian loess and sand. The sand dunes can be and often are stabilized by vegetation supported by micro-climate systems derived from interdune lakes and playas. Still, these vegetation stabilized dunes can become destabilized by perturbations to the system, perhaps increased air temperature.
    Interestingly, some of the work by Scheffer et al., (see for example Early-Warning Signals for Critical Transitions, Nature Sept 2009) suggest that there are signals which could serve as a tocsin. Increased variance is one such signal.
    Thus, even if a system is stable at such-and-such time, an external forcing can perturb the system (that of course is now unstable due to the perturbation) into an alternate more stable state; this of course is both fascinating and quite important. I suspect Dan has seen some warning signals in the realm of economics
    However, I don’t want to simplify the matter to much–to echo John von Neumann, “…in mathematics you don’t understand things. You just get used to them….”
    Many systems have thresholds that are non linear (see for example )-this can complicate study of system–this too is fascinating.
    Importantly, it should be seen that systems are often dynamic but we are beginning to develop tools to describe and understand the complicated processes and patterns. Thus, for me, hope springs eternal.