The Pinatubo ash cloud extended 35 kilometers into the atmosphere, cooling parts of the world by up to 0. Recent research has suggested that even small eruptions could be contributing to slower surface temperature rise in the last 15 years or so, compared to previous decades. Satellite images suggest the Calbuco ash cloud has reached at least 14km, Dr Anja Schmidt , a researcher in volcanic impacts and hazards at the University of Leeds, tells Carbon Brief.
Another important factor in whether a volcanic eruption influences climate is the amount of sulphur dioxide contained in the dust cloud. And the quantities can be huge. Once in the stratosphere, fast-moving winds can quickly spread the ash cloud around the world, giving a local eruption a global impact. Schmidt says right now, the priority is to ensure aviation safety by monitoring and predicting how the ash cloud disperses. Volcano eruptions can influence more than just temperature. Recent research suggests eruptions can affect the position of the Intertropical Convergence Zone ITCZ , a huge belt of low pressure that is the main source of rain for much of Africa.
Consequences were also felt far beyond Iceland. Temperature data from the U. In fact, the temperature decreased about one degree Celsius in the Northern Hemisphere overall. That may not sound like much, but it had enormous effects in terms of food supplies and the survival of people across the Northern Hemisphere.
For comparison, the global temperature of the most recent Ice Age was only about five degrees C below the current average. There are many reasons that large volcanic eruptions have such far-reaching effects on global climate. First, volcanic eruptions produce major quantities of carbon dioxide CO 2 , a gas known to contribute to the greenhouse effect.
Such greenhouse gases trap heat radiated off of the surface of the earth forming a type of insulation around the planet. The greenhouse effect is essential for our survival because it maintains the temperature of our planet within a habitable range. Nevertheless, there is growing concern that our production of gases such as CO 2 from the burning of fossil fuels may be pushing the system a little too far, resulting in excessive warming on a global scale.
There is no doubt that volcanic eruptions add CO 2 to the atmosphere, but compared to the quantity produced by human activities, their impact is virtually trivial: volcanic eruptions produce about million tons of CO 2 each year, whereas human activities contribute almost 10, times that quantity.
By far the more substantive climatic effect from volcanoes results from the production of atmospheric haze. Large eruption columns inject ash particles and sulfur-rich gases into the troposphere and stratosphere and these clouds can circle the globe within weeks of the volcanic activity.
The small ash particles decrease the amount of sunlight reaching the surface of the earth and lower average global temperatures. The sulfurous gases combine with water in the atmosphere to form acidic aerosols that also absorb incoming solar radiation and scatter it back out into space. The ash and aerosol clouds from large volcanic eruptions spread quickly through the atmosphere.
On August 26 and 27, , the volcano Krakatau erupted in a catastrophic event that ejected about 20 cubic kilometers of material in an eruption column almost 40 kilometers high.
Although volcanic aerosols provide a catalyst for ozone depletion, the real culprits in destroying ozone are human-generated CFCs. However, future volcanic eruptions will cause fluctuations in the recovery process. Volcanic eruptions can enhance global warming by adding CO 2 to the atmosphere. However, a far greater amount of CO 2 is contributed to the atmosphere by human activities each year than by volcanic eruptions. Gerlach , American Geophysical Union notes that human-made CO 2 exceeds the estimated global release of CO 2 from volcanoes by at least times.
The small amount of global warming caused by eruption-generated greenhouse gases is offset by the far greater amount of global cooling caused by eruption-generated particles in the stratosphere the haze effect.
Greenhouse warming of the earth has been particularly evident since Without the cooling influence of such eruptions as El Chichon and Mt. Pinatubo , described below, greenhouse warming would have been more pronounced. Volcanic eruptions enhance the haze effect to a greater extent than the greenhouse effect, and thus they can lower mean global temperatures.
It was thought for many years that the greatest volcanic contribution of the haze effect was from the suspended ash particles in the upper atmosphere that would block out solar radiation. However, these ideas changed in the after the eruption of the Mexican volcano, El Chichon. Although the eruption of Mt. Helens lowered global temperatures by 0. Although the Mt. Helens blast emitted a greater amount of ash in the stratosphere, the El Chichon eruption emitted a much greater volume of sulfur-rich gases 40x more.
It appears that the volume of pyroclastic debris emitted during a blast is not the best criteria to measure its effects on the atmosphere.
The amount of sulfur-rich gases appears to be more important. Sulfur combines with water vapor in the stratosphere to form dense clouds of tiny sulfuric acid droplets. These droplets take several years to settle out and they are capable to decreasing the troposphere temperatures because they absorb solar radiation and scatter it back to space. This temperature pattern is consistent with the existence of a strong phase of the Arctic Oscillation, a natural pattern of circulation in which atmospheric pressure at polar and middle latitudes fluctuates, bringing higher-than-normal pressure over the polar region and lower-than-normal pressure at about 45 degrees north latitude.
It is forced by the aerosol radiative effect, and circulation in winter is stronger than the aerosol radiative cooling that dominates in summer. Man-made, or "anthropogenic" emissions can make the consequences of volcanic eruptions on the global climate system more severe, Stenchikov says. For instance, chlorofluorocarbons CFCs in the atmosphere start a chain of chemical reactions on aerosol surfaces that destroy ozone molecules in the mid-latitude stratosphere, intensifying observed stratospheric ozone depletion.
In after the Pinatubo eruption, when the amount of CFCs in the stratosphere increased, the ozone content in the mid-latitudes decreased by 5 percent to 8 percent, affecting highly populated regions," says Stenchikov. NASA and the National Science Foundation have funded Robock and Stenchikov to study the Pinatubo eruption in more detail, and to conduct another model comparison with the volcanic aerosol data set. By understanding the impact of large volcanic eruptions on Earth's climate system in more detail, perhaps scientists will be in a better position to suggest measures to lessen their effects on people and natural resources.
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