In brief: How much do volcanoes influence the climate?
- 29 Aug 2014, 12:00
- Roz Pidcock
Overnight, a volcano in Iceland called
erupting, triggering a flurry questions about the
possible impacts for the UK and further afield.
In 2010, Eyjafjallajökull eruption in
disrupted global transport - shutting down
air traffic across Europe for several days.
Volcanoes also have an effect on the climate.
Throughout earth's history, volcanic eruptions have punctuated the
temperature record. We take a quick look at the role of volcanic
eruptions in climate - past, present and future.
A tiny contribution to global
Volcanic eruptions can affect climate in two
main ways. First, they release the greenhouse gas carbon dioxide,
contributing to warming of the atmosphere.
But the warming effect is
very small. Volcanic carbon dioxide
emissions since 1750 are at least 100 times smaller than those from
fossil fuel burning, according to the latest report from the
Intergovernmental Panel on Climate Change (IPCC).
A two-year cooling effect
As well as carbon dioxide, volcanic eruptions
also blast a cloud of ash, dust and sulphur dioxide into the
stratosphere, which is quickly blown around the globe.
Sulphur dioxide combines with oxygen and water
to form sulphuric acid "aerosols". These particles directly reflect
sunlight and encourage clouds to form.
This cooling effect outweighs the warming contribution from
carbon dioxide, causing an overall cooling that tends to lasts for
about two years after a major eruption.
NASA has shown the average effect of the five
biggest volcanic eruptions this century is a cooling effect up to
0.2 degrees Celsius, lasting for about two years.
The eruption of Mount
Pinatubo in 1991 was one of the century's most powerful eruptions.
Its huge dust and aerosol cloud
cooled parts of the world by up
to 0.4 degrees Celsius.
There have been no significant eruptions since
Mt Pinatubo in 1991, though a few small events caused fairly
significant cooling in the first decade of the 21st century. The
2010 Eyjafjallajökull eruption's effect on climate was about 10,000
times less than Mount Pinatubo.
Short term impacts, but no lasting
Overall, volcanic eruptions have had very little
influence on the temperature changes we've seen in the last
century, except for the brief period following an
Along with other natural variability, such as
ocean cycles and changes in the sun's activity, volcanic eruptions
contribute to ups and downs in global temperature from year to
Scientists think the cooling effect of volcanic
eruptions together with a drop in solar activity since about 2005
is one reason why temperatures at earth's surface have risen slower
in the last 15 years than previous decades, for example.
Most of the
so called "hiatus" in surface warming is down to natural cycles
changing where heat is stored in the ocean, pushing it into deeper
Scientists expect some large eruptions this
century but can't predict when.
Since any contribution to global temperature
will be small compared to human sources, all IPCC's forecasts for
future warming assume no major volcanic eruptions.
Based on greenhouse gas emissions alone, the
IPCC expects between 0.3 and 0.7 degrees Celsius temperature rise
by 2016-2035 compared to 1986-2005.
The huge gas, ash and aerosol cloud blasted
into the atmosphere by Mount Pinatubo in the Philippines, which
erupted in 1991. (Credit: USGS)
Consequences for Europe
While volcanic eruptions don't have a lasting effect on global
climate, evidence suggests summers in Central Europe immediately
following a major eruption are
cooler and drier than usual. By contrast, winters in Northern
Europe tend to be warmer and wetter.
Earlier this week,
The Daily Express this week suggested a
different - and rather more dramatic - outcome, saying:
could freeze in years of super-cold winters and miserable summers
if the Bardarbunga volcano erupts, experts have warned."
The Met Office says the impacts specifically for
Britain have a lot to do with which direction the winds is coming
from when the volcano erupts. At the moment, the Bardabunga
eruption hasn't produced an ash cloud, but scientists are
monitoring it closely for further activity.
Geoengineering the climate
Volcano eruptions provide an insight into what
would happen if we deliberately inject aerosols into the
atmosphere. This has been suggested by some as a way to
"geoengineer" the climate to bring global temperatures
Research suggests the impact on the global water
cycle is likely to be large. Both the African and Asian monsoons
were weaker in the year following the Mt Pinatubo eruption in