“How much carbon is emitted from tropical deforestation?” asks Daniel J. Zarin of the Climate and Land Use Alliance in the most recent issue of Science magazine. The answer may be considerably less than previously thought. A study, also in Science, based on satellite data finds that emissions from deforestation account for 10% of global carbon emissions.

While greenhouse gas emissions continue to increase, the scientific estimates of how much tropical deforestation contributes to the total are falling. REDD, it seems, is becoming less relevant either as a mechanism to prevent the destruction of the tropical forests or as a means of addressing climate change. (Of course, as a carbon trading mechanism, REDD is in any case hopeless as a means of addressing climate change because carbon trading does not reduce emissions, it just moves them from one place to another.) This does not mean that addressing deforestation and climate change are not important. Both are important. They just happen to be less related to each other than previously thought.

The new study, which was funded by a World Bank grant to Winrock International, is is titled, “Baseline Map of Carbon Emissions from Deforestation in Tropical Regions”. The lead author of the research was Nancy Harris of Winrock International. Other members of the research team are from Applied GeoSolutions, NASA’s Jet Propulsion Laboratory, the University of California and the World Bank.

In 2007, the Intergovernmental Panel on Climate Change (IPCC) came up with a “best estimate” of net carbon emissions from tropical land use change in the 1990s of 1.6 ± 0.6 petagrams of carbon per year. That amounts to about 20% of greenhouse gas emissions from human activity during the 1990s. Harris et al. produced a figure of gross carbon emissions in the tropics of 0.81 petagrams of carbon per year (with a 90% prediction interval of 0.57 to 1.22) between 2000 and 2005. “This comprises 7 to 14% of total global anthropogenic CO2 emissions over the time period analyzed,” write Harris et al.. So that’s approximately half of the IPCC estimate.

The difference between net emissions and gross emissions is that net emissions include forest regrowth. Harris et al. note that,

[A] policy mechanism that proposes to compensate developing countries for reducing emissions from deforestation and forest degradation (REDD) will benefit from estimates of emissions from gross deforestation that are disaggregated from the forest regrowth term and that do not use a priori assumptions about the fate of vegetation carbon stocks after clearing.

The Winrock International team used satellite data rather than relying on the UN Food and Agriculture Organisation’s figures for deforestation. In a press release about the Science paper, one of the co-authors, Winrock’s Sandra Brown, points out that,

“It’s time to acknowledge the problems with the FAO data and accept that we can now do much better. We have the ability, at last, to match the areas of forest clearing with their carbon stocks before clearing in much greater detail, allowing us to pinpoint more precisely where the highest emissions are occurring.”

The change from using FAO data is certainly to be welcomed. The FAO is far from a neutral collector of data on the world’s forests. Among other problems, the FAO’s Global Forest Resources Assessment includes industrial tree plantations as forests (on planet FAO, monocultures are “planted forests“). And FAO doesn’t include logging as deforestation (on planet FAO, clearcuts are “temporarily unstocked areas”).

Harris et al. found that 55% of emissions from tropical deforestation between 2000 and 2005 came from Brazil and Indonesia. They produced a map that highlights where the most deforestation was taking place (click on the image for a larger version):

Nearly 40% of total forest loss between 2000 and 2005 in our study region was concentrated in the dry tropics, but these losses accounted for only 17% of total carbon emissions, reflecting the low carbon density of these forests compared with tropical moist forests. Emissions are high in the Brazilian Amazon, but other areas of high emissions include Peninsular Malaysia, Laos, Sarawak (Malaysia), and Sumatra and Kalimantan (Indonesia) in Southeast Asia and, to a lesser extent, the Congo Basin in Africa.

CLUA’s Dan Zarin points out that Harris et al. are not the only ones to have taken another look at emissions from tropical deforestation. In January 2012, a study by Alessandro Baccini and colleagues was published in Nature Climate Change. They came up with a figure of 2.22 petagrams of carbon per year. Zarin notes drily that the difference is “cause for concern in climate policy circles”. He suggests that,

it would benefit both the science and policy communities if the two research groups could determine the reasons for the 1.41 Pg C year⁻¹ difference in their results soon, and do so with sufficient transparency for others to evaluate.

True, that would probably benefit the science and policy communities. But there are at least two other important observations to be made. First, measuring emissions from deforestation is complex and it’s going to be a while before we can do so accurately on this sort of scale. Harris el al. point out that, “emissions from land-use change … are the most uncertain component of the global carbon cycle”. Second, as a percentage of global carbon emissions, tropical deforestation emissions are decreasing because emissions from fossil fuels are increasing rapidly, while emissions from deforestation remain comparatively steady. We need to reduce deforestation urgently. But let’s not pretend that doing so is going to stop runaway climate change. If we are serious about addressing climate change we need to reduce emissions from burning fossil fuels.

UPDATE – 28 June 2012: Daniel Zarin contacted REDD-Monitor requesting that the following “factual clarifications” be provided:

• The Harris et al. (2012)* estimate of 0.81 petagrams of carbon emissions per year from tropical deforestation (equivalent to 3 gigatonnes of CO2 emissions per year) does not include peatland conversion, which would add at least an additional gigatonne of CO2 emissions per year to the estimate.
• Emissions from forest degradation (the second “D” in REDD) are also not included and are likely to be significant.
• Differences in recent estimates of emissions from deforestation referenced in my essay and cited in your post (Baccini et al 2012**; Harris et al. 2012*) are not because “measuring emissions from deforestation is complex” as stated in your post, but rather because they use different methodologies and definitions. Unpacking and explaining those differences should not take long for these talented scientists to do, and would provide a clearer understanding of what the numbers mean and how they relate to REDD+ policymaking, particularly the setting of reference levels.

*N.L. Harris et al., Science 336:1573 (2012)
**A. Baccini et al., Nat. Clim. Change 2:182 (2012)