Photo from Flickr user oobrien. Creative Commons licence.
Methane levels in the atmosphere rose steeply from the 1970s to the 1990s, but has been stable over the last ten years, until 2007, when it climbed again.
Methane is the second most important gas causing man-made climate change. It causes about 25 times more warming than carbon dioxide, but it survives for a shorter time before it is broken down, and there is less of it in the atmosphere. Overall it has about half the impact of carbon dioxide.
The stabilisation of the increasing levels has probably been the result of
- industrial reform
- changes in rice farming methods
- the capture of methane from landfill sites
One of the stations monitoring methane levels and noticing indications of an increase is Svalbard in Norway. Although this increase could be from several sources,their findings suggest that it is from natural causes:
- reversion to older rice farming methods
- drying out of tropical wetlands
- release of methane from permafrost
- from hydrate deposits on the ocean floor.
but the most likely is that it is coming from wetlands.
Cattle are often cited as sources of methane, as indeed they are, though far from the worst. There has been recent news that Australian scientists are developing a type of "burpless" grass which produces far less methane one processed by the cow. Whether this will be a successful way of reducing greenhouse emissions remains to be seen. Other scientists suggest this grass could even raise methane production from cattle.