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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