The greatest concentrations of the world's soil carbon have been pinpointed by researchers - and much of it is a dangerously flammable addition to climate change concerns.
An international scientific survey of peat bogs has calculated that they contain more carbon than all the world's forests, heaths and grasslands together - and perhaps as much as the planet's atmosphere. Since peat can smoulder underground for years, it is another potential factor in global warming calculations.
Peat is simply leaf litter that never completely decayed. Ancient peatlands become distinctive ecosystems and, in some places, an economic resource.
Merritt Turetsky, an ecosystem ecologist at the University of Guelph, Ontario, and colleagues report in Nature Geoscience that peatlands cover between only 2% and 3% of the planet's land surface, but store 25% of the planet's soil carbon.
In the high latitudes of the northern hemisphere, peat bogs cover about 4 million sq km and store between 500 and 600 billion tonnes of carbon.
In the tropics - and especially in south-east Asia - they cover about 400,000 sq km and store 100 billion tonnes of carbon. The entire pool of atmospheric carbon, in the form of carbon dioxide, adds up to about 850 billion tonnes.
Human disturbance creates peat fire threat
In its pristine condition, a peat bog is unlikely to burn: the peat exists because vegetation doesn't decay normally in water. But, over thousands of years, humans have drained the peat bogs, exploited them for fuel, and even used peat as a gardening mulch.
Dry peat burns easily, and some of the largest fires on Earth are now in the drained peatlands, says Dr Turetsky:
"When people think of a forest fire, they probably think of flames licking up into treetops, and animals trying to escape. But peat fires tend to be creeping ground fires. They can burn for days or weeks, even under relatively wet conditions. They lack the drama of flames, but they produce a lot of smoke."
The research by Canadian, British, Dutch and US scientists is part of a wider global attempt to understand the carbon cycle.
Global warming happens because more carbon goes into the atmosphere as carbon dioxide than plants in the oceans and on land can absorb. So it makes sense to work out in fine detail where the carbon comes from, and how it is soaked up by living things.
Continue reading at ENN affiliate, The Ecologist.
Peat bog image via Shutterstock.