A new study reveals an unprecedented increase in wildfires in tropical peatlands during the 20th century.
Peatlands store vast quantities of carbon below the Earth's surface - more than all the world's forest biomass combined - but when they catch fire large amounts of the stored carbon is released into the atmosphere.
Wildfires in tropical regions have been on the rise in recent decades, but the history and characteristics of wildfires in tropical peatlands remain largely unknown.
Researchers therefore analysed charcoal records preserved in peat deposits across Central and South America, Africa, Southeast Asia and Australasia to reconstruct wildfire activity stretching back more than two millennia.
Historically, peatland fire patterns are closely linked to climate fluctuations, particularly the length and severity of droughts.
The researchers found that wildfire activity in tropical peatlands declined for more than 1,000 years, in line with changes in global temperatures and other natural climate variables.
But in the last century, there was a dramatic increase in the number of wildfires, and regional differences in the results point to human activities being the root cause.
The increase in wildfires was mainly confined to the Southeast Asia and Australasian regions, where drainage for agriculture, deforestation and land conversion has left peat soils more vulnerable to ignition.
But in less accessible peatland regions across South America and Africa, there were no such increases, although lead author Dr Yuwan Wang warns these regions could experience more wildfires too as population density increases and commercial agriculture and infrastructure expands.
"To avoid large carbon emissions that further contribute to global warming we urgently need to protect these carbon-dense ecosystems," said Dr Wang from the University of Exeter.
"A reduction in tropical peatland burning could be achieved through peatland conservation, and promoting sustainable resource management and ecosystem restoration, but this requires the collaboration of multiple groups and has to be carried out at sufficiently large scale."
"Unprecedented burning in tropical peatlands during the 20th century compared to the previous two millennia" is published in Global Change Biology.
Role of pyrogenic carbon
In a separate study, the researchers provide the first estimate of the quantity of pyrogenic carbon - including charcoal and soot - in Amazonian peatlands.
Pyrogenic carbon is produced during wildfires where biomass or organic soil matter is converted into charcoal, soot or other forms of black carbon rather than being released into the atmosphere.
The chemical structure of pyrogenic carbon is more stable and resistant to decomposition than other forms of carbon, so it acts as a longer-term carbon sink.
The researchers combined their own field dataset with published sources to estimate that pyrogenic carbon makes up 1.6% of the total organic carbon stock for the Amazon basin.
This is low in percentage terms compared with higher global averages and suggests these intact peatlands are resistant to wildfires.
"The low percentage of pyrogenic carbon in Amazonian peatlands shows that fires are not a natural phenomenon in peatland systems. But even though the buildup of pyrogenic carbon through wildfires does bring some benefits in terms of more robust carbon storage in the future, we do not want to destroy these ecosystems by burning them," said lead author Yuwan Wang from the University of Exeter.
