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1st
PART
IMPACTS OF VOLCANOES ON CLIMATE A volcanic eruption of high magnitude can influence the climate in a major way for several years. Although the eruptions themselves are not predictable, however, one can get an idea of their effect on climate. Benjamin Franklin (1706-1790) was the first to see that volcanic eruptions affect climate with the harsh winter of 1783-1784 caused by the eruption of Jökull and Eldeyjar in Iceland. In the South of France the stars located above 40° of angular height in relation to the horizon were only been seen.
In the history of the Earth, the largest
volcanic eruptions were followed by a cooling of few years.
This is due to the large amount of sulfur dioxide (SO2)
and ash ejected by these volcanic eruptions. Much of the dust
and particles ascend to the stratosphere at 20.km
of altitude and sometimes at even more of 50.km.
At these altitudes, the winds are strong and the gas can often
make several times around the planet. As the
stratosphere is stable and reduced vertical movements,
the ejected gas may remain for several years. The ashes sent into the atmosphere
fall gradually in the stable high stratosphere, and helps
to increase the creation of clounds
and precipitations in
the lower atmosphere. But this is not the ashes that have
the greatest effect on climate.
When sulfur dioxide ejected into the stratosphere is mixed with water vapor in the atmosphere, then this gas turns into liquid sulfuric acid (H2S04) and becomes what is named "aerosol", ie fine droplets of a few tenths of microns in diameter. These sulfuric acid aerosols,
absorb and reflect back to space solar radiation while warming
occurs in the stratosphere, it can reach a few degrees at
the height of the layer.Then tropospheric
temperature tends to fall as was the case during many
eruptions. And sometimes this can last 2 to 3.ans
after the eruption. In general, there is a net reduction of
5 to 10% of the energy received on the surface of the Earth.
While the temperature may fall by 0,10°C to 1°C sometimes.
The global cooling triggered by these eruptions would always
initially detected under the tropics, shortly after the eruption.
Then he then propagate at mid-latitudes over the following
years.
Estimates of the fraction of sunlight transmitted through
the
Click here to see an animation of the effects of a volcanic eruption The scale of climate disruption
will depend on the place the eruption. A volcanic eruption
at the equator like the Pinatubo,
has the opportunity to reach the global climate of the Earth
since the product aerosols may extend in both hemispheres.
Aerosols prevent the heat of the sun of crossing the lowest
layer of the atmosphere (the troposphere) by cooling then
the temperature of regions near the tropics but by warming
the stratosphere. The temperatures of North and South are
reduced and AO is accelerated.
Cold air remains in the North during the winter and much of
the US Northeast is experiencing mild weather..
As can be seen in this diagram the large
eruptions lead to global cooling,
The sulfuric acid aerosols formed in the stratosphere when the sulfur dioxide combines with water particles accelerate the destruction of the ozone layer. The years following the eruption of Mount Pinatubo in 1991, the mapping of the ozone layer and other observations showed reductions of ozone more important than previous years as many in mid-latitudes and high latitudes of the northern hemisphere.
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