It''s no secret that Amazonian forest burning is a significant cause of global warming, both because the size of a huge carbon sink is reduced and because of direct emissions from the burning itself. What''s much less appreciated is that Indonesia''s emissions from biomass burning are of the same order, though somewhat smaller than Africa''s. Indonesia''s annual rate of deforestation, at an alarming 3.4 percent, is only slightly smaller than Brazil''s.
An article published this weekend by Nature Geoscience takes a shot at better specifying Indonesia''s record of biomass burning since the 1960s. It explains the spikes in the record in terms of rainfall fluctuation, demographic and social-economic trends on the country''s biggest islands, and policy. It suggests some significant policy implications.
Because satellite data were lacking before the mid-1990s, the authors rely on visibility records from regional airports to construct an index of biomass combustion. They identify two major fire episodes, in 1997-98 and 2006, and two minors ones, in 2002 and 2004. A unique element in Indonesian fires is that the bulk of the emissions result from burning of peat soils for as long as four months at a time. But the ignition of fires has been closely associated with patterns of human migration and agricultural expansion, and with related policy initiatives. For example, the rate of deforestation has climbed sharply in recent decades on Kalimantan, as industrial agriculture and forestry displaced subsistence farming, creating vulnerabilities: ''Peatlands drained under Mega Rice Project of the 1990s'were the single biggest contributor to emissions across all of Indonesia during the 1997 fire event.''
Regional workings of the ocean and atmosphere are almost equally important. Not only the famed El Nino-Southern Oscillation (ENSO), whereby the western Pacific dries when Peru floods, but also the Indian Ocean Dipole play an important role. (The dipole involves unusual cooling of sea surface temperatures in the southeastern equatorial Indian Ocean and warming of temperatures in the western equatorial Indian Ocean.) In the relatively severe 2006 and 1994 events both ENSO and the dipole were operative, but in the less severe 2002 event only ENSO.
''It is therefore important,'' the authors conclude, ''that sea surface temperature anomalies over both the Pacific and Indian Oceans be monitored in preventing and mitigating future fire events'Such mitigation measures are particularly important under a changing climate, given the possibility of more persistent El Nino-like conditions, reduced rainfall over Indonesia''s main burning regions and a positive feedback between reduced soil moisture and reduced precipitation in Indonesia.''