Rules of the road for carbon offsets: the trouble with trees


The first rule of offsets, according to Joseph Romm, is “no trees.” This is a pretty good rule, as these thing go. The TerraPass offset portfolio contains no tree-planting projects, despite the fact that most consumers love trees and the fact that tree-planting projects are typically cheaper than offsets from renewable energy projects.

So if trees are both consumer-friendly and cost-effective, why avoid them? There are lots of reasons, and Romm chooses to focus on one of the more minor ones: a recent study suggesting that trees outside of tropical zones actually cause a net increase in global warming by absorbing sunlight.

I say this is possibly the least convincing not because I have any particular insight into the quality of the study. Rather, it’s just generally true that a single study based on a novel computer simulation can at best be described as suggestive, not conclusive. We’re a long way off from fully understanding the interplay between vegetation and climate. Given the perverse policy implications of a study suggesting trees actually contribute to global warming, extreme prudence is warranted.

Regardless, many more fundamental reasons exist to be wary of trees as a source of carbon offsets. To be fair, Romm does touch on some of these in a subsequent post.

The biggest one is timing. A carbon offset represents not just a specific amount of greenhouse gas reduction, but also a specific period in which the reduction takes place. One of the most basic principles of offset quality is that, other things being equal, you want to sponsor reductions that are taking place now, not at some far-off point in the future.

Unfortunately, trees grow rather slowly. And particularly when they’re small, they don’t sequester much carbon. The small print on tree-planting offsets typically indicate a 40-year maturity. If you buy a tree-based offset today, you’re sponsoring a reduction that won’t be complete until 2047, by which time we’ll either be living in hurricane-proof seaside bunkers in the Rockies or flying around in hydrogen-fueled jet cars.

A second concern with tree-based offsets is permanence. An offset is only an offset if the reduction is real and ongoing. Trees have an unfortunate habit of dying or being cut down. Particularly given the time frames involved, with all the attendant issues over land rights, it can be very tricky to say what will happen to an individual forest several decades down the road. Some offset companies claim to guard against this risk by padding their tree offset purchases, but such tactics don’t seem to guard against large-scale deforestation.

There are additional problems with tree-planting projects, which I catalog below. But before delivering the whole list, I want to provide some perspective to this downbeat picture.

The first bit of perspective is that tree-planting projects make up an extremely small percentage of offsetting projects worldwide. For example, reforestation accounts for 6 out of 1,783 projects in the CDM pipeline. Consumers are disproportionately aware of trees because such projects make up a disproportionate share of the tiny voluntary market. As mentioned, marketers love these projects because they’re cheap and consumer-friendly. I wish this weren’t so, but it doesn’t really affect the worldwide market very greatly.

A second bit of perspective is that, despite these problems, it would be really great to bring tree-planting projects credibly into the carbon offsetting fold. Deforestation is the cause of 20 percent of anthropogenic global warming. And of course, deforestation is an environmental problem for dozens of reasons beyond just carbon emissions. Opening up another revenue stream to protect forests is an extremely worthwhile goal.

A final bit of perspective: the problems I have outlined, though serious, are not necessarily insurmountable. Organizations like the Pacific Forest Trust are trying to address issues of timing and permanence through novel offsetting protocols that rely more on forest preservation than just tree planting. Such protocols track biomass accumulation year by year, rather than front-loading future growth. The resulting offsets are far more expensive than typical tree-based offsets, but as the price of carbon rises, they will become economically viable.

So the first rule of offsets stands: unless you’re willing to do a lot of diligence, you’re best off avoiding trees. But let’s keep our fingers crossed for innovation in this area.

* * *

Postscript. For the sake of completeness, here are some further issues with tree-planting projects as a source of offsets. A third concern, after timing and permanence, is measureability. It’s fairly complicated to measure the amount of carbon absorbed by a forest; some planting practices can actually result in a net release of carbon from the soil. A fourth is the aforementioned sunlight absorption issue. A fifth is the possibility of “leakage,” which means that the new trees just displace deforestation, rather than reduce it. Sixth is a variety of well-documented quality issues with some tree plantations, such as monocultures of nonnative species, although these are addressable through proper project design.

In general, I find the fundamental issues of timing and permanence to be much more important than project-specific quality control issues, which hopefully will work themselves out in the longer term.

Update: I thought I’d pass along this tidbit from the Sierra Club:

According to Brendan Bell, the Sierra Club Global Warming and Energy Program’s representative in Washington, D.C., organizations that invest in renewable energy (like solar, geo-thermal and wind) have a definite, measurable impact and are therefore a better bet than companies focused on reforestation — because the results of planting trees are difficult to verify.

Again, this stuff is just common knowledge.

Photo available under Creative Commons license from Flickr user yaaaay.

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  1. Jill - August 1, 2007

    Given the alarming rate at which tropical forests are disappearing, why isn’t the reforestation/preservation of these included in your C offsets?

  2. Eric Ponteri - August 1, 2007

    What about protecting trees that already exist in threatened rain forests? How monetarily effective is this?

  3. Adam Stein - August 1, 2007

    There is ton of interest in “avoided deforestation” projects these days, and I expect that at some point in the relatively near future the protocols will be worked out to make these a standard component of carbon offset portfolios.
    Oddly enough, there has been some resistance to these sorts of projects from countries that would most benefit. See, for example, this recent NYT article on Brazil.

  4. RaeVynn - August 1, 2007

    This is truly hogwash.
    Trees absorb carbon dioxide to make oxygen.
    Every single tree helps to reduce CO2. Every one of them. Even in temperate regions.
    The idea that the “dark” of trees somehow absorbs sunlight, had to have come from someone that has never actually had a tree in their yard.
    Trees attract rain, which will help to alleviate drought. Trees use CO2, which will reduce levels. Trees create oxygen, which we all need to breath. Trees clean the air of pollutants.
    I’m not going to support any program that is anti-tree!

  5. Jason - August 1, 2007

    Trees attract rain?? How does that work exactly?
    I applaud Terrapass for pursuing other projects rather than tree-planting. There is nothing wrong with tree planting, but there are certainly lots of people doing it already. We need to investigate projects that reduce or remove CO2 now, and lots of it. Alternative energies, sequestration, improvements to existing technology, etc., will have an improvement both now and later.

  6. DV - August 1, 2007

    Trees vs. No Trees: I vote for trees! Common sense says they are better than the alternatives: parking lots, clear cuts, shadeless lawns, treeless housing developments. Why aren’t developers required to plant trees to replace those they cut down to build houses, condos, apartments and shopping centers? At the rate that trees are being destroyed even “outside the tropical zone” are we going to run out of our favorite oxygen producers?

  7. Adam Stein - August 1, 2007

    The idea that the “dark” of trees somehow absorbs sunlight, had to have come from someone that has never actually had a tree in their yard.
    Um…if trees didn’t absorb sunlight, they couldn’t grow, absorb CO2, generate oxygen, or do any of the other things we like about trees. Trees most certainly do absorb the sun’s light and warmth.
    Also, trees don’t “attract rain.” There’s no such thing as attracting rain. (Although in some ecosystems, trees do affect rainfall patterns through evaporative effects.)
    It seems this can’t be said too many times: recognizing that tree-planting projects are not presently a good source of carbon offsets is not the same thing as being “anti-tree.” Trees are great. They just aren’t a great source of carbon offsets.

  8. David Katz - August 1, 2007

    Your post on trees for carbon offsets could not be more incorrect or distorted. To make it worse, you reference a speculative, undocumented, largely discredited article on trees causing warming to start your discusion. Does this reflect the lack of technical understanding that is the basis for much of TerraPass’s carbon work?
    [Ed. — the post above references a scientific article in the context of criticizing it, not praising it. The rest of the post offers standard criticisms of tree-planting offsets as articulated by many other environmental organizations, such as the Sierra Club.]

  9. Ilana - August 1, 2007

    I don’t understand the “trees absorb sunlight” argument…

  10. Dennis Beeson - August 1, 2007

    Well well, Remember Easter Island ~?
    no trees = no People. Let’s compare a wind mill to a tree. Does a
    wind mill cool the planet… does a wind mill make
    oxygen… does a wind mill sequester Co2… does a
    wind mill evapotranspire to make rain…does a wind
    mill look better than a tree? does a wind mill clean the soil water & air?
    does a wind mill add pollution & fossil fuel consumption in manufacturing & construction…? does a wind mill create a multitude of products…?
    How much does a wind mill cost. I am a wind farmer ~!
    You take the temperature in the middle of a highway
    then the forest and I know the answer…….Dennis Beeson

  11. Chris Buchner - August 1, 2007

    Ilana, the argument that trees absorb sunlight in this case refers to the light coming from the sun either being absorbed by something on the earth or being reflected back into space. The importance is the issue of whether the heat in the light is absorbed or reflected. Global warming is caused by more heat being absorbed by the earth.
    Imagine a snow covered mountain – this will reflect a lot of heat because it is white. Now imagine a the same mountain with trees and snow. The amount of heat reflected by the trees and snow will be less.

  12. Ilana - August 1, 2007

    i.e. why does that make them a poor choice for carbon offseting?

  13. Ilana - August 1, 2007

    I wonder where the balance falls, when sunlight reflected is trapped in our atmosphere by GHGs so it’s better to have trees to absorb the sunlight…

  14. Mani - August 1, 2007

    I am baffled by Adam article. Every tree take in Co2, keeps the C (tree trunk) and releases the O2. Also, the sunlight not absorbed by the trees will be absorbed soil. Not a very convincing article.

  15. Adam Stein - August 1, 2007

    Hi David,
    The stuff I’m reporting is well known in the industry. Most tree-planting offsets are not regarded as a credible source of offsets by people who know something about offsets. This isn’t the TerraPass position or the result of some novel research that we’ve performed. This is just taken for granted by people who understand offsets. Once again, this isn’t a statement about the value of trees. It’s a statement about the value of trees as a source of carbon offsets.
    You’ve listed a bunch of nice thing about trees, such as urban beautification, shade, real estate appreciation, storm water control, etc. These are all good and uncontroversial aspects of trees. You have not addressed my arguments about the timing, permanence, and measurability of their ablity to sequester carbon, which are the key obstacles to creating high-quality offsets from tree-planting.
    Further, you show a basic misunderstanding of how offsets from wind farms and methane digesters work. When methane is destroyed in a digester, the offset is immediate and permanent. The lifespan of the digester itself is irrelevant. The same can not be said of a tree.
    Likewise, you show a severe misunderstanding of the co-benefits of wind farms and methane digesters. In answer to your question, yes, I have visited these facilities and seen firsthand the benefits they provide to local communities. Just because you personally haven’t benefited from these projects doesn’t mean that the benefits aren’t real.
    I encourage you to take the time to understand the technical issues involved in generating carbon offsets. It’s ironic that you accuse of focusing on marketing over technical matters, because this exchange demonstrates that the reverse is true. Consumers love trees, trees are cheap, and it would be quite easy for us to offer tree-planting offsets. The reason we forgo the marketing benefits of these projects is that they don’t meet our quality criteria.

  16. Aaron A. - August 2, 2007

    When methane is destroyed in a digester, the offset is immediate and permanent. The lifespan of the digester itself is irrelevant. The same can not be said of a tree.

    Some of these comments seem a little silly, insofar as they (a) confuse the immediate weather patterns within a farm or a forest to the global climate, or (b) confuse a discussion of trees’ CO2-sequestering ability with a referendum on trees in general. As if anybody’s actually suggesting that we should pave the planet to get rid of these dastardly trees. Stupid trees, don’t they realize we’re trying to save the planet here? </sarcasm>

    Still, I wouldn’t say that the digester’s lifespan is entirely irrelevant. They do bring up a good point about the use of resources to produce and install a digester in the first place. However, I would think that that pales in comparison to the volume of methane that such a device destroys over time; if it didn’t, then the idea would have been abandoned on the drawing board.

    — A.

  17. Jim - August 2, 2007

    Wow…lots of comments on this one. First, yes that trees cause rain (Comment No. 6 by Jason). I lived in a very rural part of lowland Panama for two years and was astonished to learn, though it now seems so obvious to me now, that when trees go away so does the rainfall. In fact, Panama relies heavily on hydroelectric. The power companies plant thousands of acres of non-native pine trees up river (pine trees, although not native, are very fast growing) in order to promote rainfall in order to turn the turbines.
    Another truism about Central America where much of the rain forest lives: people LOVE to cut down trees for any reason whatsoever. In fact, I taught English at a grade school and the little 3rd graders actually had “Machete Class”. I am not kidding! Children are taught that trees harbor all kinds of bad, and poisonous, things (which they do) including snakes, bugs, and even bad spirits, witches, and ghosts. In a land where cattle are king pastures must be cut and burned to accommodate these beasts. You can’t blame them really; we do it here in American at a much grander scale. I tried to explain that an acre of mahogany is far more valuable over the years than that same acre used for cattle. They just gave me that look that I get now when I tell people that solar power is much more efficient over the years that coal-fired electric plants, or that a hybrid, although priced higher on the sticker, will actually end up even over the long haul. And I used to think ignorance was culture specific.
    Another truism about Central America: people LOVE to cut down trees for any reason whatsoever. In fact, I taught english at a grade school and the 3rd graders actually had Machete Class. No kidding! They are taught that trees harbor all kinds of bad, and poisonous, things (which they do).

  18. alvinwriter - August 3, 2007

    Intelligent insights here. I see Adam Stein’s point, which is the fact that there’s not enough evidence to say that trees can process enough carbon dioxide in the air to counter the greenhouse effect. But on the other hand, I also agree with the others who say otherwise. Scientific fact-finding aside, I believe trees do help in keeping our planet cool.
    But the trouble with trees is that there are not enough of them left to compensate for the excess carbon dioxide being released into the atmosphere. Let’s imagine for a moment that all the trees on Earth have been cut down. Where would the carbon dioxide being released by industries and exhaled by animals and people go? We could just as easily say that the trouble with humans is that they exhale too much carbon dioxide and this amount is constantly rising because of population explosion.
    I’ll go off the beaten path a bit. You may have read of this plan by scientists to terraform Mars inthe future. This means using planetary engineering to change its atmosphere into a breathable one like the Earth’s—with lots of oxygen. How do they plan to do this? Simple. Seed Mars with blue green algae which would grow and make use of the carbon dioxide in the Martian air and release oxygen in the process. If scientists believe that a whole planet like Mars can be changed by a simple organism like algae, then I believe trees can do a lot more, and we won’t have to go to another planet to see the effects.
    While I believe that findings on how trees can help in soaking up excess carbon dioxide in the atmosphere are inconclusive, I also believe that there are not enough studies on the matter to find substantial proof of the total effect of trees on the Earth’s climate.
    This link from TheNewsRoom details long-term research done on a section of Duke forest in the US. The results show that trees do help eliminate carbon dioxide from the air even in concentrations higher than current levels. However, there are also factors that can prevent this. Read more here:
    I’m writing in from TheScienceDesk at TheNewsRoom, where you can find more global warming news. We already have a group of users interested in the subject who have found great content they have used in their sites. I thought you and the others who read this might also be interested. Email for details. We will be happy to hear from you!

  19. Adam Stein - August 3, 2007

    Intelligent insights here. I see Adam Stein’s point, which is the fact that there’s not enough evidence to say that trees can process enough carbon dioxide in the air to counter the greenhouse effect.
    Hi alvinwriter,
    Thanks for the thoughtful comment, but this is not my point at all. Trees — particularly in the tropics — are an essential carbon sink.
    My point is much narrower: most tree-planting projects don’t presently make for great carbon offsets. High-quality carbon offsets have a number of technical requirements, such as measurability, that are difficult to meet with tree-planting projects. In time, these technical hurdles may be overcome.
    Incidentally, many of the studies of the Duke forest were overseen by Bill Schlesinger, the former dean of the Duke University Nicholas School of Earth & Ocean Sciences. Bill Schlesinger serves on the TerraPass technical advisory board.

  20. martha - August 4, 2007

    Hey Adam,
    Still chewing on it all… thank you for all of the updates, info,…and for continuing to dialogue and further elucidate your points.

  21. Adam Stein - August 4, 2007

    Hi Martha,
    Let me know if you have any specific questions. Unfortunately, there aren’t a lot of great resources online for this information. I did a quick search, though, and I did find some more good info in this report (pdf).
    I’m going to write a follow-up post on offsets from avoided deforestation, which is an interesting topic in its own right.

  22. Nathan - August 6, 2007

    The “problems” listed with trees to address Greenhouse gas reductions are all being addressed very quickly by conservation organizations.
    For example, in Georgia a Carbon Sequestration Registry protocol has been developed that provides very reliable ways to measure tree carbon in most all forest types that exist in the South. The Registry provides a mechanism that updates the amount of carbon sequestration each year within specific forest stands. Trees do not grow slowly in the South. If managed appropriately, they can sequester up to 6 tons of
    CO2 eq per acre per year. Over 1 million acres of open land has been converted to forests in Georgia in the last 20 years to help forest landowners maintain a total of 24 million acres in that state alone.
    The blog author has ignored that although trees may be cut in some forests, the products made from these trees continue to store large amounts of carbon, often longer that the life of the trees. The impact on global warming on renewable products from forests or “product carbon” has been accounted for in forestry protocols from Georgia to California. This makes the concept of “leakage” in forest projects almost a non-issue.
    The “permenance” issue is also being addressed as likely the last step in making forestry projects very real and reliable. A confidence should exist in the market that forest projects will not be destroyed by development during the period where the carbon sequestration is most robust. On the one hand a project that has no long-term plans or contracts attached to the management of the forest carbon is likely to have little value. On the other hand, requiring a conservation easement in perpetuity is a dis-incentive for most forest owners who might otherwise invest in carbon sequestration management. A solution is needed at this time that provides a carbon sequestration project period that provides permenance through the critical forest growth
    period and does not drive away the majority of forest owners. Perhaps
    a 20 year project period for carbon projects is needed?? The market place continues to wrestle with this. The Georgia registry addresses permemance by requiring a detailed forest management plan with a minimum 10 year planning horizon and by recognizing restrictions on forest development.
    In summary, forest management has much affect on carbon emissions and sequestrations, forests grow quickly and are accurately measured in many parts of the world; forest growth (and carbon) can be measured each year; leakage is a non-issue on working forests; and permenance is an issue that has current focus by the market with alternative solutions very possible.

  23. Allen A. - August 6, 2007

    Nathan (#23) said:
    The blog author has ignored that although trees may be cut in some forests, the products made from these trees continue to store large amounts of carbon, often longer that the life of the trees.

    I don’t think they ignored that. Trees are good for many things; we all know that. I think that the author’s main point (correct me if I’m wrong, Adam) was that using tree-planting as a source of offsets leaves too many questions unanswered. What kind of trees are we buying? Where will they be planted? How do we know the trees are being cared for? Am I paying for CO2 offsets that won’t fully take effect until 2020? If the tree dies before maturity, will it be replaced to ensure that I get full value for my offset? These are not questions that a responsible offset provider can just shrug off.

    The Georgia registry sounds like a very promising development. Hopefully public interest in conservation will keep standardization efforts moving. As has been said numerous times on this thread, people like trees. If somebody can develop a set of standards for measuring and comparing tree projects, it could go a long way toward public acceptance of carbon offsets in general.

    — A.

  24. Anonymous - August 6, 2007

    If Terra Pass believes this story, I will be pulling myself from Terra Pass faster than you can say “photosynthesis”. You must be bored adam.

  25. Adam Stein - August 6, 2007

    Nathan — thanks for the thoughts. I did mention in the original post that these issues are being actively worked on, and it’s nice to hear that progress is being made. I do think, though, that further headway is needed. For example, I took a peek at the Georgia Carbon Sequestration Registry. As its name implies, it appears to be an offset registry, not a means of measuring carbon uptake in forests. And timing is still an issue with forestry offsets, even if the trees grow quickly. Our auditor requires that every TerraPass funds a reduction in the same time period in which it is sold. So, while I remain hopeful about forestry offsets, we’re still waiting and watching.
    One unfortunate thing about this comment thread is that people seem focused on forestry offsets as a monolithic block. In truth, there are many types of forestry offsets, ranging from tree-planting to avoided deforestation, and there is a great range of prices, reflecting in part the underlying variability in quality. In my original post, I did not treat these projects as monolithic, but instead said that they require a lot of diligence. I expect that that will remain true for a while longer.