Indonesia fires: The volunteer firefighters risking their lives to defuse 'carbon bombs'

But what makes Borneo's fires particularly worrying is the fact that they are burning through one of the world's largest tropical peatland ecosystems.

This 4.5-million-hectare swathe of forest and swamp, under normal conditions, serves as a valuable reservoir for ancient carbon.

When these peatlands catch fire, they risk releasing millions of tonnes of carbon dioxide, carbon monoxide and methane into the atmosphere – a "pulse" of greenhouse gas emissions that has earned them the sobriquet of "carbon bomb".