Decades of satellite observations show that in an average year, wildfires around the world burn an area equivalent to the size of India and emit more carbon dioxide to the atmosphere than global road, rail, shipping and air transport combined.

As vegetation in burned areas regrows, it draws CO₂ back out of the atmosphere through photosynthesis. This is part of the normal fire-recovery cycle, which can take less than a year in grasslands or decades in fire-adapted forests.

In extreme cases, such as arctic or tropical peatlands, full recovery may not occur for centuries.

This recovery of vegetation is important because carbon that is not re-captured stays in the atmosphere and contributes to climate change.

Deforestation fires are a particularly important contributor to climate change as these result in a long-term loss of carbon to the atmosphere.

Now a new study by wildfire researchers at Swansea University and Vrije Universiteit Amsterdam has quantified the important role that charcoal created by fires - known as pyrogenic carbon - plays in helping to compensate for carbon emissions.

Their paper Global fire emissions buffered by the production of pyrogenic carbon, has just been published in Nature Geoscience.

Lead author Dr Matthew Jones said: “CO₂ emitted during fires is normally sequestered again as vegetation regrows, and researchers generally consider wildfires to be carbon neutral events once full biomass recovery has occurred.

“However, in a fire some of the vegetation is not consumed by burning, but instead transformed to charcoal. This carbon-rich material can be stored in soils and oceans over very long time periods.

“We have combined field studies, satellite data, and modelling to better quantify the amount of carbon that is placed into storage by fires at the global scale.”

The paper, which was co-authored by Dr Cristina Santin and Professor Stefan Doerr, of the College of Science, and Professor Guido van der Werf, of Vrije Universiteit Amsterdam, explained that, as well as emitting CO₂ to the atmosphere, landscape fires also transfer a significant fraction of affected vegetation carbon to charcoal and other charred materials.

The researchers say this pyrogenic carbon needs to be considered in global fire emission models.

Matthew Jones, who is now at the University of East Anglia, said: “Our results show that, globally, the production of pyrogenic carbon is equivalent to 12 per cent of CO₂ emissions from fires and can be considered a significant buffer for landscape fire emissions.

“Climate warming is expected to increase the prevalence of wildfires in many regions, particularly in forests. This may lead to an overall increase in atmospheric CO₂ emissions from wildfires, which in most cases will be recaptured by vegetation regrowth in future decades.

 “However, the production of pyrogenic carbon essentially removes some carbon from the atmosphere for centuries, or possibly even millennia.

“This brings some good news, although rising CO₂ emissions caused by human activity, including deforestation and some peatland fires, continue to pose a serious threat to global climate.”

There are still important questions to be answered about how a warmer, more drought-prone climate will affect global burned areas in the future.

For example, will there be more fire in arctic peatlands as we are experiencing this summer or what proportion of CO₂ emissions will be recaptured by future vegetation regrowth?

But this new research shows that pyrogenic carbon production should be considered as a significant product of fires and an important element of the global carbon cycle.