There is a sign that methane is showing some increase
Geir Braathen, WMO
Noaa figures show CO2 concentrations
rising by 2.4 parts per million (ppm) from 2006 to 2007. By comparison,
the average annual increase between 1979 and 2007 was 1.65ppm.
Concentrations now stand at 384 ppm, compared
to about 280 ppm before the era of human industrialisation began.
Upwards curve?
The rise in CO2 is not exceptional compared
with the previous few years, but does add more evidence that concentrations
are rising faster than they were a decade or so ago.
The methane figure is more interesting, and
potentially of more concern.
Concentrations have been more or less stable
since about 1999 following years of rapid increases. Industrial reform
in the former Soviet bloc, changes to rice farming methods and the capture
of methane from landfill sites all contributed to the levelling off.
But the 2007 figure indicates that levels
may be on the rise again.
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"Looking at the curve, there is a sign
that methane is showing some increase," commented Geir Braathen, senior
scientific officer with the World Meteorological Organization, who was
not involved in the Noaa publication.
But the mechanism behind that would be
uncertain; and it's too early to say if this is the start of a new increase
or not.
"We will need several years of increase
before we can state that there is a rising trend."
Warming trend
Methane concentrations have shown small rises
and falls during the years of stability, but rises have been associated
with El Nino conditions which are known to induce more wildfires.
Currently, the world is experiencing La Nina
conditions,
the opposite of El Nino.
A sustained rise could be due to several reasons.
Asia's spectacular industrialisation, reversion to older rice farming techniques,
and a drying out of tropical wetlands would all be candidates if the rising
trend is confirmed.
Equally possible would be the release of methane
from frozen zones of the world, notably the Arctic permafrost, as they
warm.
Methane is the second most important gas causing
man-made climate change. Each molecule causes about 25 times more warming
than a molecule of CO2, but it survives for shorter times in
the atmosphere before being broken down. |
