What influence do forest, peat and grassland fires have on climate change?
Wildfires burn each year an area roughly equivalent to the size of the EU, leading to the emission of aerosols and greenhouse gases. Guido van der Werf, professor of Global Carbon Cycle Studies at VU Amsterdam, investigates the relationship between wildfires and climate change. His work provides a basis for improved wildfire management, and hence reduced emission of greenhouse gases.
It has been estimated that about 500 million hectares are affected by fires annually throughout the world. Many of these fires are started deliberately in forests, peatland and grassland by farmers or plantation owners, in order to clear new land for agricultural purposes. “Most fires burn in African savanna,” says Prof. Van der Werf. “Apart from that, large areas of tropical forest have been burnt to make room for soy and palm oil production and cattle grazing. There is less intentional burning of tropical forest nowadays in some countries, largely as a result of the tightening up of the environmental regulations. In addition, many savannas have been converted to agricultural land lowering the use of fire there. But at the same time climate change with warmer conditions and more frequent droughts may lead to an increase of fires in the far north, for example the Canadian, Siberian and Alaskan tundra.”
Satellite and drone images
Prof. Van der Werf’s research group are using satellite and drone images to map the extent of wildfire throughout the world and convert those estimates to emissions of greenhouse gases and aerosols. They also study smoke composition using bags suspended from the drones. This allows them to measure the concentration of aerosols and greenhouse gases such as carbon dioxide, methane and nitrous oxide in the samples. The results of these measurements are used to model the effect of wildfires on climate.
Global fire data
Guido van der Werf was a co-founder of the international database Globalfiredata.org twenty years ago. This database provides a platform for the dissemination of research results on emissions due to wildfires throughout the world. Its scope has been substantially expanded since then, and it is now used by NGOs, government agencies, the Intergovernmental Panel on Climate Change (IPPC) and other researchers. Between about 300 and 400 scientific publications on climate change, making use of information from this database among other sources, are published every year.
Prof. Van der Werf is also involved in various international programmes aimed at improving the management of savanna regions. “Most savanna fires burn late in the dry season” he explains. “If we ignite the fires earlier in the dry season, however, there is less chance that fires will get out of control, they are less extreme, and burn patchier. This prevents emissions of the greenhouse gases methane and nitrous oxide and may be better for biodiversity as well.”
Five per cent
Van der Werf’s research group estimates that the overall contribution of wildfires, more specifically those used in the deforestation process, to increasing concentrations of greenhouse gases is about five per cent, but the story is complex. ”Greenhouse gas emissions lead to a rise in global temperature,” says Prof. Van der Werf. “Aerosols, on the other hand, have a cooling effect. One of the key research questions in this field is to determine the balance between these two effects. Once we have an answer to this question, we will be able to estimate the contribution of wildfires to climate change more accurately.”