Earth’s rotation, not human activity caused methane level increase

A new study has suggested that it’s not human activity but the Earth’s rotation patterns that caused an increase in methane levels 5000 years ago.

Dr Joy Singarayer of the University of Bristol, and colleagues, suggest changes in the Earth's orbit and precession, not agriculture, played a major part.

The team used computer models, used to estimate future climatic conditions, to trace back over the past 130,000 years and then used this data to estimate vegetation types, and hence methane production, across the planet.

Singarayer and colleagues found the output of their models matched with measurements of methane from ice cores taken in Greenland.

"What we found was that our models were able to reproduce both the decrease that was seen around 100,000 years ago and the increase we've seen in the last 5000 years, without having to invoke human induced emissions through agriculture," ABC Science quoted Paul Valdes, also of the University of Bristol, as saying.

According to Valdes, the computer models showed wetlands in the Southern Hemisphere, in particular South America, were the source of the additional methane.

"This was based on the fact that this had some of the biggest changes in monsoon and because the land area is so large," he said.

Valdes added that given the models "did a good job of simulating past changes in methane ... [it] will maybe give us a little more confidence that the computer models are working correctly and therefore more believable for future predictions."

CSIRO Marine and Atmospheric Research scientist, Dr David Etheridge said, "[They] did a reasonably good global climate simulation across those periods. They don't rule out early anthropogenic causes, but they say that it can still be explained from wetlands."

He says one of the concerns for the future is how feedback of atmospheric methane may amplify global warming, and that studies like this will help us better understand the releases of methane that can cause them.

The study was published in Nature.