Forests: the fire next time

Forests: the fire next time

24 February 2012

published by

Global/World Health Organisation — The combination of a predicted increase in heatwaves and the carbon stored in the world’s soils is reason for alarm

Forest fires are a fact of life, and in some regions an important part of the natural ecosystem, but that does not make them welcome. Wildfire sears an astonishing 350 to 400 million hectares each year: this is an area of land greater than the surface of India. The economic costs of bushfires are prodigious – one sustained blaze in Texas in 2011 did damage estimated at $5bn – but the human costs, too, are cruel. A team led by Tasmanian and Canadian scientists has just made a careful estimate of the contribution of dioxins, soot and other tiny airborne particles from blazing scrub and foliage to global mortality; they have established an annual estimate of around 340,000 extra deaths per year from respiratory and other diseases, chiefly in sub-Saharan Africa and south-east Asia.

According to the World Health Organisation, the smoky stoves and open fires that the world’s poorest people use to cook their meagre suppers account for up to 2 million extra deaths a year, so by comparison the wildfire component is modest – but it is likely to rise, and go on rising. That is because it is predicted that global warming will increase the frequency and intensity of heatwaves and droughts in decades to come. In the climate change scenario, yesterday’s extremes will become normal summer events, and tomorrow’s heatwaves will set new records. In temperate and arid regions, forests and other ground cover will become increasingly dry, and increasingly at risk from fire, started either deliberately or by accident, or sparked by electrical storm. Heatwaves are bad enough – they dramatically affect crop yields – but there are deeper reasons for alarm.

Most of the potential natural fuel in the world is not on the surface, but bunkered in the soil below. The dead and decaying foliage of 10,000 years is now stored as peat, and peat burns. In 1997 a fire in the rainforests of Indonesia set alight to the metres of peat below the roots, and this smouldered for months. By the time the fire was extinguished it had released greenhouse gases equal to between 20% and 40% of total worldwide emissions that year from factory chimneys and motor exhausts.

Accidental rainforest fires are rare events, but there are huge stores of peat under the forests of the north, and these are increasingly at risk. In 2007, 1,000 square kilometres of tundra caught fire in Alaska: such fires, once established, can smoulder through the winter under a blanket of snow, and then flare up again in the spring. Since the carbon stored in the world’s soils is far greater than the burden locked away in the trees above ground, any such blaze could only fuel yet more global warming, making the world an increasingly dangerous place. The smoke signals are ominous.

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