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.
First, they release the greenhouse gas carbon dioxide, contributing to warming of the atmosphere. But the effect is very small. Emissions from volcanoes since are thought to be at least times smaller than those from fossil fuel burning.
Second, sulphur dioxide contained in the ash cloud can produce a cooling effect, explains Prof Jim McQuaid , professor of atmospheric composition at the University of Leeds:. At around 2 minutes in you can see the impact of the volcanic eruption in Madagascar, just off the eastern coast of Africa. Not all volcano eruptions are the same. Volcanic eruptions are rated from zero to eight on a scale of explosivity , measured by the amount of ash and debris they produce.
Before Calbuco, the most recent significant volcano eruption was Mount Pinatubo in the Philippines in June This was rated as a six, while the first of the Calbuco eruptions has been rated as a four or five, according to a minister of the Chilean Government. However, it is an indirect role, which cannot be directly attributed to volcanic HCl.
Eruption-generated particles, or aerosols, appear to provide surfaces upon which chemical reactions take place. The particles themselves do not contribute to ozone destruction, but they interact with chlorine- and bromine-bearing compounds from human-made CFCs.
Fortunately, volcanic particles will settle out of the stratosphere in two or three years, so that the effects of volcanic eruptions on ozone depletion are short lived.
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.
Aubry and his colleagues used models of both climate and volcanic plumes to simulate what happens to aerosols emitted by a volcanic eruption in the present climate and how that could change by the end of the century with continued global warming. In their models, all the eruptions occurred at Mount Pinatubo. They found that for moderate-magnitude eruptions, the height at which sulfate aerosols settle in the atmosphere remained the same in a warmer climate.
This discrepancy has less to do with volcanic emissions and more to do with the atmosphere: The height of the stratosphere is predicted to increase with climate change.
Aerosols from moderate volcanic eruptions will therefore be more likely to remain in the troposphere and be removed by rain, reducing their potency. For large eruptions, models indicated that volcanic plumes will rise around 1. This change in elevation will result in the aerosols spreading faster around the world.
This increase in aerosol spread is mainly due to a predicted acceleration of the Brewer-Dobson circulation, which moves air in the troposphere upward into the stratosphere and then toward the poles.
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