Humans responsible for much higher methane emissions than estimated

It mightn't get the attention that carbon dioxide does, but methane is a highly potent greenhouse gas that we know to be a powerful contributor to global warming. A new study suggests we may have been severely underestimating how much human activity is driving it into the atmosphere, however, uncovering evidence that human-caused methane emissions are as much as 40 percent higher than previously estimated.

While methane isn't nearly as abundant in the atmosphere as carbon dioxide, it is much more effective at trapping heat, making it more than a bit-part player in climate change. The gas can arise from many sources, such as the fertilizer industry, agriculture, fossil fuels and the production of oil and gas, and new analysis from an international team of researchers indicates we have been emitting far more than we thought.

The project, led by scientists at the University of Rochester and involving researchers from Australia's CSIRO, involved using advanced mass spectrometry techniques to study isotopes in air trapped in the Antarctic and Greenland ice sheets since pre-industrial times.

More specifically, the researchers detected and counted the carbon-14 isotope in the samples, which is absent from natural sources of methane such as geological seepage, and could therefore be used to distinguish between these sources and the methane generated by human activity.

This was combined with data collected from ice core samples that were used to track trends in methane sources over the last 200 years. This new analysis revealed that pre-industrial sources of emissions were only a fraction of what we previously thought them to be, at most around 10 percent of our earlier estimates.

This suggests that as we entered the industrial age things picked up considerably, with modern, human-related sources of methane making up a far larger portion, as much as 25 to 40 percent more, according to the researchers, who have found a silver lining to the new findings.

"The additional methane emissions now attributed to fossil fuel are consistent with recent research quantifying the methane coming from coal mines, oil and gas production, and fossil fuel use," says Dr Etheridge. "These findings help to reduce uncertainty and present a significant opportunity to mitigate greenhouse gas emissions. Being a relatively short-lived gas compared to carbon dioxide, atmospheric concentrations of methane would respond quickly to reduced emissions."

The research was published in the journal Nature.

Source: CSIRO