Volcanoes & Climate
- ' Consequently, the sulfur compounds have a greater
short-term effect, and cooling dominates. However,
over long periods of time (thousands or millions of years),
multiple eruptions of giant volcanoes, such as the
flood basalt volcanoes, can raise the carbon dioxide
levels enough to cause significant global warming.'
Volcanoes & Climate
Volcanic eruptions can alter the climate of the earth for both short and
long periods of time. For example, average global temperatures dropped
about a degree Fahrenheit for about two years after the eruption of Mount
Pinatubo in 1991, and very cold temperatures caused crop failures and
famine in North America and Europe for two years following the eruption
of Tambora in 1815. Volcanologists believe that the balance of the
earth's mild climate over periods of millions of years is maintained by
ongoing volcanism. Volcanoes affect the climate through the gases and
dust particles thrown into the atmosphere during eruptions. The effect of
the volcanic gases and dust may warm or cool the earth's surface,
depending on how sunlight interacts with the volcanic material.
Volcanic dust blasted into the atmosphere causes temporary cooling. The
amount of cooling depends on the amount of dust put into the air, and the
duration of the cooling depends on the size of the dust particles.
Particles the size of sand grains fall out of the air in a matter of a
few minutes and stay close to the volcano. These particles have little
effect on the climate. Tiny dust-size ash particles thrown into the lower
atmosphere will float around for hours or days, causing darkness and
cooling directly beneath the ash cloud, but these particles are quickly
washed out of the air by the abundant water and rain present in the lower
atmosphere. However, dust tossed into the dry upper atmosphere, the
stratosphere, can remain for weeks to months before they finally settle.
These particles block sunlight and cause some cooling over large areas of
Volcanoes that release large amounts of sulfur compounds like sulfur
oxide or sulfur dioxide affect the climate more strongly than those that
eject just dust. The sulfur compounds are gases that rise easily into the
stratosphere. Once there, they combine with the (limited) water available
to form a haze of tiny droplets of sulfuric acid. These tiny droplets are
very light in color and reflect a great deal of sunlight for their size.
Although the droplets eventually grow large enough to fall to the earth,
the stratosphere is so dry that it takes time, months or even years to
happen. Consequently, reflective hazes of sulfur droplets can cause
significant cooling of the earth for as long as two years after a major
sulfur-bearing eruption. Sulfur hazes are believed to have been the
primary cause of the global cooling that occurred after the Pinatubo and
Tambora eruptions. For many months, a satellite tracked the sulfur cloud
produced by Pinatubo. The image shows the cloud about three months after
the eruption. It is already a continuous band of haze encircling the
entire globe. You can learn more about the cooling effects of sulfur
hazes by clicking here.
Volcanoes also release large amounts of water and carbon dioxide. When
these two compounds are in the form of gases in the atmosphere, they
absorb heat radiation (infrared) emitted by the ground and hold it in the
atmosphere. This causes the air below to get warmer. Therefore, you might
think that a major eruption would cause a temporary warming of the
atmosphere rather than a cooling. However, there are very large amounts
of water and carbon dioxide in the atmosphere already, and even a large
eruption doesn't change the global amounts very much. In addition, the
water generally condenses out of the atmosphere as rain in a few hours to
a few days, and the carbon dioxide quickly dissolves in the ocean or is
absorbed by plants. Consequently, the sulfur compounds have a greater
short-term effect, and cooling dominates. However, over long periods of
time (thousands or millions of years), multiple eruptions of giant
volcanoes, such as the flood basalt volcanoes, can raise the carbon
dioxide levels enough to cause significant global warming.
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