The second Icelandic volcanic eruption in a month has catapulted tonnes off ash into the atmosphere. High altitude westerly winds have spread the ash plume as far as 1000km from the volcano itself closing major airports across Europe- and leaving thousands of travellers stranded.
The atmosphere is broken up into various levels depending on their temperature profiles. The troposphere is the first 10km of the atmosphere and this is where all our weather happens. The next level is the stratosphere, a stable layer with very little weather. The boundary between these two layers is known as the tropopause and large aircraft usually fly just above this boundary since the absence of "weather" provides calm conditions and little turbulence.
When a volcano erupts, it often spews up a huge amount of ash with such great force that tiny particles reach as far as the stratosphere. Even if the ash isn't visible, this poses a problem for aircraft as it can enter the engines and cause damage, electrical failures and faulty instrument readings. This is the primary reason why many airports across Europe have closed today.
Volcanic eruptions can also have a significant impact on the short-term climate. A large amount of ash in the atmosphere can effectively act as a barrier against solar radiation leading to a period of cooling. The most recent example of this is the 1991 eruption of Mount Pinatubo in the Phillipines- it's ash cloud dropped the average temperature by 0.4-0.5 degrees.
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