Uncontrolled coal-seam fires are catastrophic polluters

Subterranean fires are almost impossible to extinguish and add to global emissions from fossil fuels

The longest-lasting fire known in the world, thought to date back at least 5,500 years, is burning beneath Mount Wingen in New South Wales. The blaze burns in a coal seam that may once have been exposed on the ground and set alight by lightning.

Since then the fire has been smouldering, eating into the coal seam at a rate of about 3ft (1 metre) each year, but because it is about 100ft deep underground the fire is almost impossible to extinguish and will probably continue to burn long into the future.

There are thousands of uncontrolled underground fires in the world, largely coal seams ignited by human-made fires, lightning or spontaneous combustion from chemical reactions.