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The BBC's Environment Correspondent,
Richard Black, analyses whether Volcano eruptions have an impact on
Climate Change. Watching the enormous plumes of dust and ash
rising from Eyjafjallajokull, it is hard to imagine that this almost
week-long eruption would not have any effect on weather and climate.
But that is the likelihood; that the impact on Britons, Europeans
and the citizens of the wider world will be limited to cancelled
flights, with no other effects on the skies.
Volcanoes produce tiny particles - aerosols - which have a net
cooling effect on the world because they reflect solar energy back
into space.
They also produce carbon dioxide, a greenhouse gas.
Historically, the cooling has outweighed the warming. The 1991
eruption of Mount Pinatubo in The Philippines lowered global
temperatures by about 0.4-0.5C - but Eyjafjallajokull, dramatic as
it looks, is simply not in that league.
"Icelandic scientists have made a first estimate of the volume of
material ejected, and it's about 140 million cubic metres," says
Mike Burton from Italy's National Institute of Geophysics and
Vulcanology.
"That's a lot in five days; but Pinatubo ejected 10 cubic
kilometres - that's 100 times as much.
"So this is not the big climate changing eruption that some people
seem to think it is."
As well as the sheer volume of aerosols, the other factor
influencing the size of its climatic impact is the altitude they
attain.
If material reaches the stratosphere, it can remain aloft for
several years; but if it stays in the troposphere, the lowest layer,
it tends to come back to Earth in days or weeks.
"At the moment, the eruption cloud reaches around 22,000 feet
(7km)," says Anja Schmidt from the School of Earth and Environment
at the UK's Leeds University.
"That's high enough to affect aviation but is unlikely to be high
enough to have a strong effect on the climate system."
Low carbon life
Dr Burton's team has spent more than a decade refining methods for
measuring the gas output from volcanoes, and made a trip to Iceland
in early April, before the Eyjafjallajoekull eruption began but
after the earlier, less vigorous spell of activity at nearby
Fimmvorduhals.
They found Fimmvorduhals was producing about 20-25,000 tonnes of CO2
each day.
Based on the relative size of the volcanoes, he estimates that
Eyjafjallajoekull could have emitted about 10 times that amount per
day at its peak.
But that lasted for less than a week; things now appear to be much
quieter.
And even over that peak period, its daily CO2 output was only about
one-thousandth of that produced by the sum total of humanity's
fossil fuel burning, deforestation, agriculture and everything else.
In fact, the extra CO2 produced from the volcano is probably less
than the volume "saved" by having Europe's aeroplanes grounded.
But any precise comparison of those two effects will depend on the
eventual duration of the grounding as compared with the eventual
duration and intensity of the eruption.
The last Eyjafjallajokull eruption lasted for two years, and it is
possible that this one will do the same; whether it does or not is
anyone's guess at present.
"But the thing to realise is that there are already a number of
volcanoes around the world, including Etna and Popocatepetl, that
are continually outgassing CO2 now," says Dr Burton.
"The amount of CO2 output still pales into insignificance beside
human emissions."
The Italian team is planning another trip to Iceland as soon as
travel conditions allow, to get more precise measurements of gas
emissions from Eyjafjallajokull.
Weather whys
Ash in the sky, but no aeroplanes: a recipe, you might think, for a
change in the weather.
When US authorities banned flying following 9/11, the temperature
difference between night and day over the continental US increased
by at least 1C.
Jet contrails were effectively acting as cirrus clouds, researchers
concluded - reflecting solar energy in the day, acting as a blanket
by night.
But nothing of that kind has been observed following the
Eyjafjallajokull eruption - or indeed any other impact on weather,
according to UK Met Office scientist Derrick Ryall.
"Given the size of the eruption, we wouldn't expect any impact,
except perhaps around Iceland itself," he says.
"If it goes on for a few months, someone will certainly be keeping
an eye on it but it would be hard to ascertain - you'd need some
pretty sophisticated analysis."
Dramatic though the pictures from Eyjafjallajokull have been, the
likelihood is that history will not rank it as a volcano that shook
the world - not a Pinatubo, not a Krakatoa, and definitely not a
Toba - the eruption some 70,000 years ago that apparently brought on
a six-year global freeze.
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