not fossil fuels, has been the most likely source of rising methane
emissions during the last decade, according to research published
is a potent greenhouse gas, and anthropogenic emissions have
increased its concentration in the atmosphere to more than twice the
fifth of the total human-made greenhouse effect has been attributed
fossils fuels were to blame for the increase during the last century,
NIWA atmospheric scientist Hinrich Schaefer said the main source of
methane since 2007 had most likely been agriculture, either from
livestock or from rice paddies.
concentrations had increased steadily since the industrial
revolution, in step with growth in the use of fossil fuels, as
methane was the main component in natural gas.
between 1999 and 2006, methane levels reached a plateau, which could
be explained through the economic collapse of the former Soviet Union
and the decline in oil production.
2007, they started climbing again.
Schaefer said the NIWA group collected methane measurements at the
clean-air monitoring station at Baring Head, near Wellington, and at
Arrival Heights in Antarctica, but with only Southern Hemisphere data
to go on, they joined forces with international colleagues to look at
possible sources of the recent increase.
clean-air monitoring station at Baring Head is where the data for
this study were collected.Photo: Dave
Allen / NIWA
team used carbon isotope analysis, a chemical fingerprinting method
that allows scientists to distinguish between three sources of
methane: burning, for example through forest fires, fossil fuels and
microbial production, either in wetlands, waterlogged rice paddies or
the rumen of livestock.
Schaefer said the discovery that the most recent increase in methane
emissions was coming from agriculture came as a surprise.
that time, the US started fracking and we also know that the economy
in Asia picked up again and coal mining increased. However, that is
not reflected in the atmosphere.”
studies had pinpointed the geographic source of the methane as the
region that included south-east Asia, China and India, areas
dominated by rice production and agriculture.
said the research highlighted that it was important to target
agricultural sources of methane at least as much as fossil fuel
related emissions, if we wanted to mitigate climate change.
fuels were not off the hook, as any “additional increase in fossil
fuel production would lead to an even faster rise in atmospheric
methane”, Dr Schaefer said.