Forests: A Rising Global Climate Superpower?

Despite increasing crop and timber demands to feed a growing human population, despite the impacts of climate change on forests, and despite deforestation emissions in the tropics that are on par with those from the global transportation sector, global forests are a net sink for atmospheric carbon.   Photo: Mark Godfrey

Despite increasing crop and timber demands to feed a growing human population, despite the impacts of climate change on forests, and despite deforestation emissions in the tropics that are on par with those from the global transportation sector, global forests are a net sink for atmospheric carbon. Photo: Mark Godfrey

By Bronson Griscom, Director of Forest Carbon Science

We just topped 400 ppm of CO2 in the atmosphere.  That’s a 40% increase since 1750, and a good bit above the 350 ppm boundary that has been identified for playing it safe (Hansen et. al., 2008).

There’s another statistical threshold we just passed that hasn’t raised the same warning alarms in the scientific community, but it makes me even more uncomfortable, on a gut level: over 50% of earth’s ice-free land surface is now anthropogenic.  In other words, there are more crops, pasture, plantations, and strip malls than there are native forests (28%) and other natural ecosystems (19%) (Hooke et. al. 2012).

It’s hard to say if we’ve yet crossed scientifically justified planetary boundaries. I’m just saying that it makes me nervous, and I don’t want to learn the hard way.

So, I am one who advocates for getting back to 350ppm for CO2 and back to 50%+ for nature.  I make the case here that forests are a big part of the solution.

Both of these problems, and their solutions, are linked.  During the agricultural revolution, conversion of forests and other ecosystems to crops was the largest source of rising CO2 concentrations.  Despite the massive scale of fossil fuel emissions in the 21st century, emissions from forest destruction continue to play a significant role in climate change. The last IPCC report (2007) concluded that nearly 20% of greenhouse gas emissions come from tropical forest destruction alone.  Likewise, efforts to Reduce Emissions from Deforestation and forest Degradation and enhance sequestration (REDD+) in the tropics have been darlings of private and public green funding, since they offer a solution to both climate change and biodiversity loss.

Recently, however, there seems to be a growing sense of concern that REDD+ is a fading star as a solution to climate change.  This may be due to both (i) the absence of a global climate deal has that was anticipated to create global financing for REDD+, and  (ii) a declining contribution of net emissions from tropical deforestation to climate change, now down to about 10% (average of Pan et. al. 2011, Baccini et. al. 2012, and Harris et. al. 2012).

I believe both of these concerns are unfounded.  It should come as no surprise that a global climate deal has been hard to reach – it requires an unprecedented level of voluntary financial and legal commitment in concert by most countries on earth to address a slow moving (albeit massive) environmental threat.

Sadly, I believe that the relentless escalation of climate change impacts that we are witnessing will make this commitment more palatable when the next opportunity for a global climate deal rolls around in 2020, or soon thereafter.

As for the scale of forests’ influence on our climate, net tropical deforestation emissions are not a good indicator of the forest climate opportunity.  Let’s review the basics of global climate flows.  Natural processes account for the vast majority of gross flows of greenhouse gases, a whopping 96% according to the IPCC (Denman et. al. 2007), with a disproportionate role played by forests.  A lot of this is the breathing in and out of natural systems (like seasonal tree leaf off and leaf on) which are in equilibrium.  And this balance of nature explains why nature dominates the gross carbon flux story, yet humans are entirely responsible for the net increase in CO2.

In fact, nature is counter-balancing the human impact, as earth’s lands and oceans are absorbing about half of human carbon emissions (Denman et. al. 2007).  One third to one half of the sink is on land, and much of that land sink is forest.  This represents an existing economic subsidy from nature worth hundreds of billions of dollars in terms of climate mitigation (Canadell and Raupach, 2008; Le Quéré et. al. in review).

The statistic that only about 10% of global CO2 emissions are due to net tropical forest loss emissions is a red herring too often the focus of discussion within the forest climate community.

This statistic conflates two more important statistics: 1) gross emission from destruction of tropical forests constitutes about 20% of global anthropogenic CO2 emissions according to the three most recent studies (Pan et al. 2011; Baccini et al. 2012; and Harris et al. 2012), and 2) gross sequestration from tropical secondary forests already offsets over 15% of our CO2 emissions, not to mention sequestration by temperate forests which are nearly as large (Fig. 1).

Gross emissions tell us the scale of the opportunity for avoided emissions, and gross sequestration tells us about the scale of the current offset from nature that could be enhanced.

Consider this: despite increasing crop and timber demands to feed a growing human population, despite the impacts of climate change on forests, and despite deforestation emissions in the tropics that are on par with those from the global transportation sector, global forests are a net sink for atmospheric carbon.  This is because:

(1) a large-scale re-growth of secondary forests in both temperate and tropical regions (Pan et. al. 2011; Canadell and Raupach, 2008), and

(2) evidence of considerable net sequestration in “intact”  tropical forests, which we have long assumed to be carbon neutral (Pan et. al. 2011; Wright, 2013).

In graphical form, here’s what it looks like:

Figure 1: My graphical representation of numbers presented in table form by Pan et. al. (2011).  The nearly net zero emissions from tropical forests shown in the left-hand bar chart are unpackaged in the right-hand bar chart which shows the large tropical gross emissions from deforestation and forest degradation, as well as large sequestration by secondary and intact forests.  Note that Pan et. al. estimate higher gross tropical deforestation emissions than Baccini et. al. (2012) and Harris et. al. (2012).

Figure 1: My graphical representation of numbers presented in table form by Pan et. al. (2011). The nearly net zero emissions from tropical forests shown in the left-hand bar chart are unpackaged in the right-hand bar chart which shows the large tropical gross emissions from deforestation and forest degradation, as well as large sequestration by secondary and intact forests. Note that Pan et. al. estimate higher gross tropical deforestation emissions than Baccini et. al. (2012) and Harris et. al. (2012).

So, nature is hard at work mitigating climate change, even if human society is not. Forests are already acting as a major solution to climate change, despite taking it on the chin from human activities.

Not only are forest ecosystems a net sink, they also currently store twice the amount of carbon that is in the atmosphere (Canadell and Raupach, 2008). This represents a large risk, because forest carbon is vulnerable to climate change.  There is mounting evidence of this vulnerability, in particular due to drought and fire (Allen et. al. 2010). Despite these threats, there is surprising evidence that the land-forest sink is increasing (Ballantyne et. al. 2012).

Does this large role of forests in the greenhouse gas story translate to a large opportunity for an affordable forest solution to climate change?  A recent UNEP report estimates that, based on least-cost scenarios, forests offer about 1/5 of the global opportunities for reaching our goal of limiting climate change to 2⁰C (UNEP 2012).  This is based on emissions reductions opportunities by avoiding forest destruction.  Others argue that the combined opportunity of avoided emissions and enhanced sequestration (e.g. planting forests and extending logging rotations) offers 1/3 of the global least cost climate mitigation opportunities (Sohngen & Mendelsohn, 2003), and that sequestration mitigation opportunities are on par with avoided deforestation opportunities (Canadell and Raupach, 2008).

To summarize, forests are a climate superpower with large opportunities for addressing climate change for three reasons:

1)      Forests store double the amount of carbon that sits in the atmosphere.  At the very least we’d better hold on to the remaining forests;

2)      Forests already play an important role in mitigating climate change, with a net sequestration of four billion tons of CO2 per year, which seems to be growing (Ballantyne et. al. 2012) despite large emissions from forest destruction in the tropics (Figure 1, Pan et. al. 2011).

3)      Forests are a large part of the solution to climate change.  Forests can provide about 20-30% of global climate mitigation under least-cost scenarios (UNEP 2012, Sohngen & Mendelsohn, 2003).

Considering all the other values of forests beyond carbon (water filtration, flood control, biodiversity, ozone absorption, timber production, etc.), we should go beyond the above least-cost studies concluding that forests are price-competitive machines for mitigating 20-30% of climate change.

Under a dream scenario where tropical deforestation and degradation was halted, and a global program was launched to double forest sequestration through reforestation, low impact logging, and extended rotations, forests could offset over half of global human CO2 emissions (my back of the envelope math based on Pan et. al. 2011).

This might just be possible if we can expect declining global farmland alongside increasing food production (Ausubel et. al. 2013), and if we can convince the McDonalds Hamburglar to switch to cultured beef (Tuomisto and Teixeira, 2013).

Of course I am also banking on break-out success of a variety of forest-climate strategies The Nature Conservancy and our global partners are pioneering.  All told, I’m optimistic that part of our solution to climate change will be bringing nature back to 51%, with forests as a rising global climate superpower.


Allen, C. et. al. 2010. A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests. Forest Ecology and Management. 259: 660-684.

Ballantyne, A. et. al. 2012. Increase in observed net carbon dioxide uptake by land and oceans during the past 50 years. Nature. 488:70-73.

Canadell, J., Raupach, M. 2008. Managing forests for climate change mitigation. Science 320: 1456-1457.

Denman, K.L., et. al. 2007: Couplings Between Changes in the Climate System and Biogeochemistry. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Hansen et. al. 2008. Open Atmos. Sci. J. (2008), vol. 2, pp. 217-231

Harris et. al. 2012. Baseline map of carbon emissions from deforestation in tropical regions.  Science 336: 1573-1576.

Hooke, R., Martín-Duque, J., Pedraza, J. 2012. Land transformation by humans: A review. GSA Today 22 (12): 1-10

Hughell, D. and R. Butterfield, 2008. Impact of FSC Certification on Deforestation and the Incidence of Wildfires in the Maya Biosphere Reserve. Rainforest Alliance. New York, NY.

Le Quéré, C. et. al. In Review. The global carbon budget 1959–2011, Earth Syst. Sci. Data Discuss., 5, 1107-1157, doi:10.5194/essdd-5-1107-2012, 2012

Pan, Y., et. al. 2011. A large and persistent carbon sink in the world’s forests. Science 333: 988-993.

Somanathan, E., Prabhakar, R. , Mehta, B.S. 2009. Decentralization for cost-effective conservation. Proceedings of the National Academy of Sciences 106 (11): 4143-4147.

Sohngen, B., Mendelsohn, R. 2003. An optimal control model of forest carbon sequestration. Amer. J. Agr. Econ. 85(2): 448–457

Tuomisto, H., Teixeira de Mattos, H. J., 2013. Environmental impacts of cultured meat production. Journal of Environmental Science and Technology.

UNEP 2012. The Emissions Gap Report 2012. United Nations Environment Programme (UNEP), Nairobi.

Wright, S. 2013. The carbon sink in intact tropical forests. Global Change Biology. 19: 337-339.

Opinions expressed on Cool Green Science and in any corresponding comments are the personal opinions of the original authors and do not necessarily reflect the views of The Nature Conservancy.
Bronson Griscom serves as Director of Forest Carbon Science for the Climate Team at The Nature Conservancy (TNC). The team’s research measures the success of TNC’s tropical forest conservation programs in Indonesia, Brazil, and Mexico in counter-acting climate change. Bronson designs and implements research to quantify the success of conservation initiatives in reducing CO2 in our atmosphere by storing carbon in forests. He completed a Ph.D. in tropical forest ecology from the Yale School of Forestry and Environmental Studies in 2003.

Comments: Forests: A Rising Global Climate Superpower?

  •  Comment from Michael Wolosin

    Great summary of some complicated numbers, Bronson. I’d like to see on the chart or in the text how your estimate of 20% gross emissions plus the gross 15% sequestration adds up to 10% net emissions.

  •  Comment from Mark Trexler

    It’s interesting to see the periodic cycling of the same kinds of discussions and numbers. I did some of the first studies of forestry mitigation opportunities while at the World Resources Institute more than 20 years ago (see for example Keeping It Green: Tropical Forestry Opportunities published in 1994), and they were extensively incorporated into the IPCC’s Second Assessment Report which argued that forestry was indeed an important part of the solution. There’s no question about the potential of land-use and forestry related measures to stem CO2 emissions and sequester additional CO2. The problem, and the reason that these potentials are not being acted upon, has always stemmed from 2 variables: 1) it is FAR more difficult than it appears from satellite land use maps to actually influence land-use decision making on the ground; 2) it is FAR more expensive to accomplish land-based CO2 mitigation than most of the least-cost models suggest. I attended an EPRI workshop were modelers argued that one could reduce up to 3 billion tons of emissions at a cost of about $3/ton. Simply silly numbers. So yes, forestry is important. But like everything else decision-making responds to the incentives in place. And the incentives are no more in place to favor REDD+ and forestry-based mitigation than they are to favor large scale energy transformations. We need to change the incentives, and that can really only happen through policy.

  •  Comment from Warwick Manfrinato

    YES, certainly a very useful information. Useful for dialogue with decision-makers and policy-makers that could help some of the barriers to be overcome. Nonetheless, the incentives are unbelievably scarce. Recently (2012) we were able to finalize e 70,000 hectares of REDD+ in a very sensitive area in the Amazon. If incentives were at hand, we could have a full certainty to hold nearly 30 million tons of CO2 from reaching the atmosphere in the next few years (a starting point). An effort that could become very cost effective given the fact that at a cost/opportunity analysis it would be likely the forest owner would prefer to simply turn it into cattle or agriculture activity. Forest management can make ends meet if logs are sold at an average of US$ 250/m3. Today, if lucky, they might get US$ 130/m3 (logs). We spent 3 years on the drawing board to reach verification of VCUs at VCS, and a small, almost irrelevant amount of VCUs, was sold to an off-taker. Costs were recovered of putting the process in place. But no one came to the “shop” to at least look at the rest of VCUs. Thus, owners were attracted to the upside of carbon to keep on the forest management, but to a deceiving outcome. It would become an interesting story if carbon had a value/incentive…but without it, huh, no way!! This year, owners are already at the point of not harvesting wood in spite all the efforts put forth to grade their operation to an FSC certification process which concluded in 2013 (necessary to the VCS registry). If it doesn’t work here, I see no chance of working any were else. Do you Bronson? Here, we are soon seriously looking at the prospect of a cattle ranching or agriculture expansion, even with the bright side of a legal deforestation. A ghost under the bed to all of us. This project was a shop-window, a guine-pig, to a larger area of 2 million hectares of other surrounding owners interested in it… So we are not talking about either a natural reserve threatened by a lacking government role or some indigenous people land being invaded by illegal loggers. We are talking about landowners, with full control over their land (presence and legal) who sat in tedious meetings, listening to our economic and environmental arguments and with dawning eyes of perpetuating their lands as forests, for the next generations. Up to the previous generations, every one in these families knew that if they didn’t deforest, there would be a higher risk of either invasion or even government appropriation. So, deforestation is the only way to secure ownership (regardless of good or bad documentation). REDD lines up in the landowner’s minds: intent, legality, higher purpose (planetary), and perpetuates forests. I simply see no reason why this doesn’t work. Some people are not doing their job right!!!!

  •  Comment from Ben Alexandro

    Interesting article. I just had the pleasure of meeting with Heru Prasetyo, head of Indonesia’s National REDD+ Agency and head of President’s Delivery Unit on Development in Jakarta this month about how to implement REDD on the ground in Indonesia. More here:

    I hope to work more on the issue with the GLOBE program this summer.

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