Carbon emissions from tropical deforestation and regrowth based on satellite observations for the 1980s and 1990s

Abstract

Carbon fluxes from tropical deforestation and regrowth are highly uncertain components of the contemporary carbon budget, due in part to the lack of spatially explicit and consistent information on changes in forest area. We estimate fluxes for the 1980s and 1990s using subpixel estimates of percent tree cover derived from coarse (National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer) satellite data in combination with a terrestrial carbon model. The satellite-derived estimates of change in forest area are lower than national reports and remote-sensing surveys from the United Nations Food and Agriculture Organization Forest Resource Assessment (FRA) in all tropical regions, especially for the 1980s. However, our results indicate that the net rate of tropical forest clearing increased approximately 10% from the 1980s to 1990s, most notably in southeast Asia, in contrast to an 11% reduction reported by the FRA. We estimate net mean annual carbon fluxes from tropical deforestation and regrowth to average 0.6 (0.3-0.8) and 0.9 (0.5-1.4) petagrams (Pg).yr(-1) for the 1980s and 1990s, respectively. Compared with previous estimates of 1.9 (0.6-2.5) Pg.yr(-1) based on FRA national statistics of changes in forest area, this alternative estimate suggests less "missing" carbon from the global carbon budget but increasing emissions from tropical land-use change.

Fig 1.

Difference in PTC for a portion of Latin America for the 1980s (difference in median PTC of 1982–88 and 1988–92, Upper Left) and 1990s (difference in median PTC of 1988–92 and 1992–99, Upper Center) and a portion of tropical Asia for the 1980s (Lower Left) and 1990s (Lower Right). The difference in percent forest cover for 1986–92 was derived from Landsat analyses, aggregated to 8-km grid cell size, for the Brazilian Amazon based on data from the Tropical Rainforest Information Center (Upper Right). Dark gray in Upper Right indicates locations of missing data (within Amazon basin) or locations where analysis was not carried out (outside Amazon basin). Negative values (red) indicate a decline in tree cover, and positive values (blue) indicate an increase.

Fig 2.

Net carbon-flux estimates for tropical land-use change for the 1980s (diagonal stripes) and 1990s (dotted pattern). Error bars are derived from sensitivity to initial biomass values at ±25% of the value given in the bookkeeping model and the ranges derived from the correction factors between PTC estimates and high-resolution analyses. In addition to carbon fluxes from forest clearing and regrowth, the carbon-flux estimate includes an additional 7% to incorporate fluxes from logging and other processes not detectable with high-resolution analyses. To compare with previously published carbon-flux estimates, these estimates include countries listed in table 3 of ref. for the regions of South and Central America, tropical Africa, and south and southeast Asia.