How bad is global deforestation?

One of the themes of the Copenhagen Synthesis Report (available here) by a group of university researchers associated with the IPCC, is the impact of global deforestation on total CO2 emissions.

Regrettably, the Report’s material on deforestation and on the role of forests in the carbon cycle is short on data and analysis. The Report contents itself with a reference to the IPCC estimate (Fourth Assessment Report) that deforestation contributes about 15 of total anthropic emissions but ignores the current scientific controversies relevant to that estimate: especially the question of the rate and distribution of deforestation and whether tropical forests are net carbon emitters or sinks.

Prof Roger Pielke Jr. (not a ‘skeptic’ about AGW) attacks the Synthesis Report for sloppy science and a personal misrepresentation. His father, Prof. Roger Pielke Sr. (more skeptical) ticks off other gross inaccuracies. Statistician David Stockwell details a convenient manipulation of the surface temperature outlook by one of the leading Copenhagen researchers in a series of posts starting here.

I’ve never looked closely at the allegation that forests (especially tropical forests) are disappearing, although anyone who has experienced the great Malay Peninsula smoke hazes (due to Indonesian burning-off) either on the ground or flying across the region, must be tempted to find the allegations of a general disaster plausible. As it turns out, only a little research shows that the overall scale and emission-impacts of deforestation is unclear and the data thin and subject to revision.

A place to start is the NASA Earth Observatory site that summarizes the known and unknown:

On the scale of the problem:
“Some scientists and conservationists argue that the FAO provides too conservative an estimate of rates of deforestation because they consider any area larger than one hectare (0.01 square miles) with a minimum tree cover of 10 percent to be forested. This generous definition of ‘forest’ means that a significant amount of degradation can occur before the FAO categorizes an area as deforested. On the other hand, some satellite-based studies indicate deforestation rates are lower than even the FAO reports suggest. In the FAO’s most recent forest assessment report, published in 2005, the organization itself revised downward the deforestation rates for the 1990s that it reported in 2001. Despite revisions and discrepancies, the FAO assessment is the most comprehensive, longest-term, and widely used metric of global forest resources.” Extract from Tropical Deforestation : Feature Articles
On the emission-impacts:
“It is not certain whether intact tropical forests are a net source or sink of carbon. Certainly, the trunks of trees are a large, stable pool of carbon that grows as forests mature or regenerate on previously cleared land. But trees, plants, and microorganisms in the soil also respire, releasing carbon dioxide as they break down carbohydrates for energy. In the Amazon, huge volumes of carbon dioxide escape from decaying leaves and other organic matter in rivers and streams that flood large areas of forest during the rainy season. Undisturbed tropical forests may be nearly neutral with respect to carbon, but deforestation and degradation are currently a source of carbon to the atmosphere and have the potential to turn the tropics into an even greater source in coming decades” Extract from Tropical Deforestation : Feature Articles

FAO survey/sensing for 2005 assessment

The FAO, which is responsible for collecting the data on forest extent, provides its current (2005) data in different summaries available from the Forestry Division. This is the adjusted data to which NASA (above) refers. As the spreadsheets show, much of it is based on relatively old and apparently imperfect data collection methods. For example, the spreadsheet reveals that in the five-years leading up to the 2005 report, only 25 countries/regions of 230 (admittedly including the biggest ‘deforesters’ and ‘reforesters’) were surveyed using ‘remote sensing’; forest change in the others was estimated by other surveys or ‘expert estimates’. FAO’s planned 2010 survey should be much more accurate

What does the data from FAO tell us? I’ll leave it to you to download the survey data, but here are a few of my observations:

  • The ‘annual rate of change’in forest extent as estimated by FAO is very small: in 2000-2005 it was less than one-fifth of one percent of the total forest extent (7.3 million hectares).
  • The deforestation rate is falling from an annual rate of 0.22 percent in 1990-2000 to 0.18 percent in 2000-2005
  • In the biggest ‘deforesters’ (Brazil and Indonesia), however, the annual rate of forest loss has risen (from 0.5 to 0.6 percent per year in Brazil)
  • In contrast, some of the biggest ‘re-foresters’ such as China—whose total forest extent is a little less than half that of Brazil—have seen their annual rate of re-forestation grow from 1.2 percent to 2.2 percent per year over the same periods.

The extract from the spreadsheets that I have made (click the thumbnail at the top of this post) to illustrate the worst of the de-forestation estimated by FAO shows:

  • The twenty-seven top de-foresters (I used a 100k ha. cut-off) have a higher, not a lower rate of deforestation than the rest of the world
  • Weighting their hectares ‘lost’ to forest by their share of global forests they accounted for an annual 0.257 percent loss of global forest in 1990-2000, and an annual loss of 0.281 percent of global forests in 2000-2005 (their higher rate of loss was offset by gains in forest coverage in 56 countries, led by China)

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