Arctic scientists
have reported that the speed at which the northern ice cap is melting
risks triggering 19 climate tipping points, with disastrous
consequences. It could also affect ecosystems elsewhere on Earth,
perhaps irreversibly. The Arctic Resilience Report says it is crucial
to reduce greenhouse gas emissions
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Methane
concentrations are higher in the northern hemisphere because both
natural- and human-caused sources are more abundant there.
Photograph: AIRS/Aqua/Nasa
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Rapid
rise in methane emissions in 10 years surprises scientists
Methane
warms planet 20 times as much as similar CO2 volumes but lack of
monitoring means scientists can’t be sure of sources
Fiona Harvey
Monday 12 December
2016 13.29 GMT
Emissions of the
powerful greenhouse gas methane have surged in the past decade,
threatening to thwart global attempts to combat climate change.
Scientists have been
surprised by the surge, which began just over 10 years ago in 2007
and then was boosted even further in 2014 and 2015. Concentrations of
methane in the atmosphere over those two years alone rose by more
than 20 parts per billion, bringing the total to 1,830ppb.
This is a cause for
alarm among global warming scientists because emissions of the gas
warm the planet by more than 20 times as much as similar volumes of
carbon dioxide.
In the meantime,
emissions of carbon dioxide – the main component of manmade
greenhouse gases in the atmosphere – have been levelling off. The
new research, published in the peer-review journal Environmental
Research Letters, suggests that the world’s attempts to control
greenhouse gases have failed to take account of the startling rises
in methane.
The authors of the
2016 Global Methane Budget report found that in the early years of
this century, concentrations of methane rose by only about 0.5ppb
each year, compared with 10ppb in 2014 and 2015.
The scientists
speculate that agriculture may be the main source of the additional
methane that has been recorded. However, they cannot be sure of all
the sources, owing to a lack of monitoring.
At least a third of
methane comes from the exploitation of fossil fuels, including
fracking and oil drilling and some coal mining, where methane is
viewed as a waste gas and is frequently allowed to escape or, in some
cases, flared off, which is less harmful.
Unlike carbon
dioxide emissions, however, which have been tracked in various ways
since the 1950s, emissions of methane are poorly understood and could
represent a threat that scientists have still not accounted for.
For instance, the
melting of the Arctic tundra releases methane as the vegetation
underneath is gradually and sometimes suddenly exposed. This has been
regarded by scientists as a potential “tipping point” whereby
warming of the Arctic leads to greater releases of methane, therefore
greater warming, in a runaway and uncontrollable cycle.
Comparison of
methane over Alison Canyon, California, acquired 11 days apart in
January 2016 by (left) Nasa’s Aviris instrument on an ER-2 aircraft
at 4.1 miles altitude and (right) by the Hyperion instrument on
Nasa’s Earth Observing-1 satellite in low-Earth orbit.
Although the world’s
governments pledged at Paris last year to hold global warming to no
more than 2C above pre-industrial levels, few have yet explained in
detail how their intentions will be worked out. The president-elect
of the US, Donald Trump, has also cast doubt on the US’s future
participation in the emissions cuts required.
Robert Jackson,
professor of earth system science at Stanford University, and a
co-author of the paper, warned that methane should also be a key
focus of attempts to control climate change.
“The levelling off
we’ve seen in the last three years for carbon dioxide emissions is
strikingly different from the recent rapid increase in methane.
Unlike CO2, where we have well-described power plants, almost
everything in the global methane budget is diffuse. From cows to
wetlands to rice paddies [as well as other sources], the methane
cycle is harder.”
“Why this change
has happened is still not well understood,” added Marielle Saunois,
assistant professor at the University of Versailles Saint Quentin,
and a lead author of the paper. “For the last two years especially,
the growth rate has been faster for the years before. It’s really
intriguing.”
As well as measures
that can be quickly implemented to prevent methane emissions from the
fossil fuel industry, ways to cut emissions from agriculture are also
being developed and implemented. New breeds of rice require less
flooding in paddy fields, new feeds can cut down on emissions from
cows, and there are methods of capturing methane from large
agricultural barns where livestock are intensively reared. However,
few of these are yet widely in operation.
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