Satellite data has shown that harmful carbon emissions from forest loss around the world may be up to 70 percent less than prior estimates, US researchers said Thursday.
The findings are based on US space agency satellites and not self-reported estimates provided by individual nations, which have formed the basis for most prior data, said the study in the journal Science.
The result is a picture of gross carbon emissions from forest loss that is about a third of previous estimates for the 2000-2005 period.
None of this data includes any positive effects from forest regrowth.
“These results serve as a more accurate benchmark for monitoring global progress on reducing emissions from deforestation,” said the study led by the non-profit environmental group Winrock International in Virginia.
Co-authors came from NASA, the University of California Los Angeles, the University of Maryland, Applied GeoSolutions in New Hampshire and the World Bank.
The study used satellite images to systematically match areas of global forest loss to their carbon stocks, or the amount of carbon these regions stored prior to clearing.
Researchers came to a gross emissions estimate of 0.81 billion metric tons of carbon released per year from deforestation.
A separate, prior study that incorporated satellite data with nationally reported estimates to the Global Forest Resources Assessment of the United Nations Food and Agricultural Organization (FAO) estimated 2.22 billion metric tons of emissions per year.
Most published estimates of carbon emission rely on this model, also known as tabular bookkeeping, which was developed in the 1980s. But lead author Nancy Harris said it may be time for a new approach.
“Tabular bookkeeping models for carbon accounting from land-use change were the best approach at the time they were developed,” said Harris.
“But the emergence of Earth-observing satellites combined with an international policy focus on reducing emissions from deforestation in developing countries has pushed the scientific community to adopt more transparent methods and increasingly spatial approaches to carbon accounting.”
Most of the forest loss — 54 percent — was in Latin America. South and Southeast Asia followed with 32 percent and sub-Saharan Africa accounted for 14 percent.
Brazil and Indonesia produced the highest emissions between 2000 and 2005, and together made up 55 percent of total emissions from tropical deforestation, the study said.
An accompanying commentary by Daniel Zarin of San Francisco’s Climate and Land Use Alliance described the difference in figures between satellite data and combined tabulation as “surprising.”
Zarin said the reasons for the stark gap were not “immediately apparent… particularly given the similarity between the underlying forest carbon stock data.”
However, the data may provide an independent assessment that could help nations better gauge their carbon footprints in the future, he said.
The United Nations Framework Convention on Climate Change allows for the voluntary establishment of benchmarks for assessing developing country performance in reducing emissions from deforestation and forest degradation (REDD+).
“Independent monitoring against reliable deforestation emission benchmarks like those reported by Harris et al., would help to underpin the integrity of these and other ‘payment for performance’ REDD+ arrangements and provide an unbiased assessment of tropical deforestation emission reductions,” Zarin wrote.