20% of CO₂ emissions from deforestation? Make that 12%

Global deforestation accounts for nearly 20 per cent of all CO₂ emissions. Everyone knows that. We’ve read it over and over again. The figure comes from the Intergovernmental Panel on Climate Change. But recent research takes a new look at the data behind the figure and comes up with a figure of around 12 per cent.

The research, carried out by Guido van der Werf at the Faculty of Earth and Life Sciences, VU University Amsterdam and colleagues, is published in Nature Geoscience this week. Van der Werf explains that “While the IPCC estimates were based on the best available information during the time of writing, several deforestation emission assessments have been revised downward since then. In addition, fossil fuel emissions have increased substantially but deforestation emissions remained relatively constant.”

In the paper, titled “CO₂ emissions from forest loss”, the authors write that,

Within the science and policy communities, carbon emissions from deforestation and forest degradation have been estimated to account for about 20% of global anthropogenic CO₂ emissions. A recalculation of this fraction using the same methods, but updated estimates on carbon emissions from both deforestation and fossil fuel combustion suggests that in 2008, the relative contribution of CO₂ emissions from deforestation and forest degradation was substantially smaller, around 12%.

A graph in the paper, illustrates the problem clearly. Since 1980, emissions from fossil fuels have increased from about 5.2 Pg C/yr to about 8.5 Pg C/yr. Meanwhile, revised data on emissions from deforestation and forest degradation indicate that emissions from forests are lower than the IPCC’s 2007 figure. Van der Werf and his colleagues recalculated the figure using the same methods as the IPCC but using updated values for deforestation. They came up with a figure of 1.2 Pg C/yr, or about 23 per cent less than the figure the IPCC produced in 2007.

“So instead of contributing 20% to total anthropogenic CO₂ emissions, 12% seems a more justifiable number nowadays (albeit with large uncertainty),” says Van der Werf. In the paper, Van der Werf and his colleagues write that “Taking into account the large uncertainties in the deforestation and degradation estimates, the range becomes 6–17%.”

The authors argue that emissions from peatlands should be included in any REDD agreement:

Land degradation that does not involve changes in tree cover density, such as oxidation and combustion of deforested and drained tropical peatlands, may also involve substantial carbon emissions. However, losses of these non-forest carbon stocks are not generally included in deforestation and forest degradation assessments, as summarized in the 2007 report of the Intergovernmental Panel on Climate Change (IPCC) Working Group I, nor are they considered in policies aiming to reduce emissions from deforestation and forest degradation (REDD).

The authors also point out the problem with the UN’s definition of “forest”, which fails to differentiate between native forests and industrial tree plantations:

[R]eplacing peat forest with oil-palm plantations may not change the tree cover density, but it does lead to a large pulse of CO₂ emissions because of reductions in both tree biomass and soil carbon.

The authors summarise their research as follows:

In short, the maximum reduction in CO₂ emissions from avoiding deforestation and forest degradation is probably about 12% of current total anthropogenic emissions (or 15% if peat degradation is included) — and that is assuming, unrealistically, that emissions from deforestation, forest degradation and peat degradation can be completely eliminated. Therefore, reducing fossil fuel emissions remains the key element for stabilizing atmospheric CO₂ concentrations.

Van der Werf says that “reducing deforestation may not be at the cost of reducing fossil fuel emissions.”

Of course this does not mean that we do not need to stop deforestation. “Even our revised estimates represent substantial emissions, and for about 30 developing countries, including Brazil, Bolivia, Indonesia, Myanmar and Zambia, deforestation and forest degradation are the largest source of CO₂,” Van der Werf and his colleagues write. But it is difficult to imagine a clearer explanation of why the carbon stored in forests should not be traded against continued greenhouse gas emissions. To prevent runaway climate change we need to stop burning fossil fuels and stop deforestation. We cannot trade off one against the other.