Deforestation over the past fifty years mapped out using smoke from forest fires

Published: 14 June 2018

More and better data about deforestation during the past half century provide a clearer picture of the respective roles of humans and the climate in fires in tropical forests and the carbon cycle worldwide. Until now, there was a great deal of uncertainty about the emissions caused by forest fires and deforestation between the 1960s and the turn of the century, when better data from satellites became available. Hydrologist Margreet van Marle therefore developed a method for mapping out tropical deforestation and forest fires over the past fifty years in both space and time.

Satellite data and weather stations

Until now, estimates of deforestation have been based primarily on data supplied by the countries themselves, as a result of which it was often not known where the deforestation was located and when it took place. Margreet van Marle used satellite data to identify spatial deforestation patterns. She then linked those data to datasets that were sometimes unusual, such as information about visibility from weather stations in the Amazon and Indonesia, and amounts of charcoal in soils. In that way, she was able to determine levels of deforestation and carbon emissions from forest fires in a consistent way from the 1960s through to the present. Levels of deforestation and the associated emissions in tropical areas in the middle of the last century proved to be lower than previously thought and they have increased sharply since. That has implications for the analysis of the global carbon cycle over the past fifty years.

Smoke from forest fires in Bolivia and Brazil, as observed by the MODIS satellite during the 2010 fire season. Source: NASA, Jeff Schmaltz

Forest fires and deforestation

Forest fires are often a natural phenomenon but they also represent a threat to people. They emit greenhouse gases into the air, and that is particularly true of the fires that cause deforestation. Emissions caused by forest fires also affect human health. Emissions from deforestation account for approximately 10% of fossil-fuel emissions, with South America accounting for approximately half.

Margreet van Marle has also shown that deforestation and forest fires in South America have increased sharply over the last fifty years, particularly in the Amazon. In addition, satellite images show that the more recent decline in deforestation in Brazil has been partly offset by an increase in deforestation in other South American countries. Van Marle developed a historical dataset with information about forest fires that will be used for the new climate forecasts.

Margreet van Marle will be awarded a PhD by the VU on 14 June.

Download the thesis: Historic Deforestation and Fire Dynamics: Quantifying their carbon emissions to better understand the global carbon cycle.