Methane the greenhouse gas-Box 1

Published by

Australian Academy
of Science

Excuse me! The problem with methane gas

Box 1 | Methane levels

Since the pre-industrial era (from around 1750) there’s been a 250 per cent increase in the amount of methane in the atmosphere. Methane levels in the pre-industrial era were some 715 parts per billion (ppb), compared to 1,774 ppb in 2005. Ice core samples show that current levels are the highest in the last 650,000 years. The current increase in methane levels is due to human activities, mainly agriculture and the use of fossil fuels.

Scientists breathed a gaseous sigh of relief when global methane levels steadied out during the 1990s. But their relief was short-lived, with a recent study revealing levels started to increase again in 2007.

The concern is that methane levels may rise dramatically if global warming increases. Higher temperatures would cause melting of permafrost in the northern hemisphere. As organic matter from long-dead plants and animals is released from the thawing permafrost and becomes covered by water, more methane would be produced by microbes.

The warming of oceans may also release vast quantities of methane into the atmosphere as methane hydrates in ocean floor sediments break up (Box 2: The oceans’ massive methane reserves).