Challenges to estimating carbon emissions from tropical deforestation

Abstract

An accurate estimate of carbon fluxes associated with tropical deforestation from the last two decades is needed to balance the global carbon budget. Several studies have already estimated carbon emissions from tropical deforestation, but the estimates vary greatly and are difficult to compare due to differences in data sources, assumptions, and methodologies. In this paper, we review the different estimates and datasets, and the various challenges associated with comparing them and with accurately estimating carbon emissions from deforestation. We performed a simulation study over legal Amazonia to illustrate some of these major issues. Our analysis demonstrates the importance of considering land-cover dynamics following deforestation, including the fluxes from reclearing of secondary vegetation, the decay of product and slash pools, and the fluxes from regrowing forest. It also suggests that accurate carbon-flux estimates will need to consider historical land-cover changes for at least the previous 20 years. However, this result is highly sensitive to estimates of the partitioning of cleared carbon into instantaneous burning vs. long-timescale slash pools. We also show that carbon flux estimates based on 'committed flux' calculations, as used by a few studies, are not comparable with the 'annual balance' calculation method used by other studies.

The importance of three centuries of land-use change for the global and regional terrestrial carbon cycle

“…4). Firstly, the difference is both the result of different deforestation (2003), as given by Ramankutty et al (2007). Studies included in the figure represent the emission ranges given in Table 2 estimates and the consideration of afforestation.…”

“…Although it is too early to state that Houghton (2003) had overestimated historical deforestation (Denman et al 2007), the rates are 30% to 60% higher than in most other studies. The high deforestation rates, based on national reports/statistics, were often compiled without checking consistency between countries (see also Denman et al 2007;Ramankutty et al 2007). Secondly, Houghton (2003) used fixed C densities for different land-cover categories, whereas these vary in time and space due to climate variation, different stages of the ecosystem (i.e.…”

“…The model also includes many feedbacks between atmosphere and the terrestrial system (Leemans et al 2002). By using this C-cycle model in a geographically explicit manner and applying it to the historical land-use data set HYDE (Klein Goldewijk 2001), we establish a consistent experimental set-up that meets the criteria, as defined by Ramankutty et al (2007). Moreover, the geographical explicitness of this approach enables a regional comparison of the major C fluxes.…”

“…The number of uncertainties, as mentioned above, have led to the recommendation by Ramankutty et al (2007) to develop more coherent and consistent landuse emission estimates using three criteria: (1) consider the full land-cover dynamics during and following deforestation (including effect on soil carbon); (2) consider explicitly historical land-use changes, and (3) accurately estimate the fate of cleared carbon. Only a methodology applying these three criteria is believed to deliver "realistic" estimates of the role of historical land-use change in the global carbon cycle.…”

“…Third, different methodologies have been used in estimating the historical land-use emissions. Houghton (2003), Fearnside (2000a, b) and Ramankutty et al (2007), for example, used book-keeping methods with fixed C densities to estimate historical land-use emissions, ignoring feedback mechanisms between atmospheric CO 2 , climate and terrestrial C dynamics. This approach leads to high emissions, since compensating responses by the terrestrial system are ignored.…”