Last 14th of April, 2010, EyjafjallajÖkul volcano located in Iceland erupted after a devastating earthquake and it was noted as the second largest eruption of 21st century. There was another earthquake close to that area on 20th of March. The second earthquake which occurred on 14th of April was 10-20 times bigger than the previous one. Before this recent eruption this volcano erupted several times during the period between 1821-1823.
Iceland sits on a volcanic hotspot in the Mid-Atlantic ridge. So, frequent eruptions occur in the area. In this recent eruption, about 6 km high ash clouds threw up in to the atmosphere and those ash particles have spread in a vast area.
There was a similar incident occurred on 15th of June, 1991 in a area called Luzon in Philippines. The Pinatubo a stratvolcano erupted after a chain of earthquakes, throwing 20 million tons of SO2 and ash particles in to 20 km up in the atmosphere. This SO2 and ash clouds had caused many changes in the global climate for a long period. Because of those ash clouds, average temperature in northern hemisphere decreased in to 10 centigrades. Also northern hemisphere had reduced temperature from 0.5-0.6 centigrades and entire planet was cooled from 0.4-0.5 centigrades. This was the first time scientists experienced such a thing in near history and they called it global cooling or cooling effect. As you may think, Yes, it is the opposite of global warming. There is no wonder, if you are amused.
There is just a simple scientific explanation for this. The SO2 gas eject from the volcano react with water/H2O(g) in the atmosphere and form Sulfuric gas/H2SO4(g). Then Sulphuric gas turn in to Sulfate aerosols. These particles can last for 3-4 years in the upper part of the atmosphere (Stratosphere) and have the ability to absorb terrestrial radiation. And also sulfate aerosol and ash particles reflect extraterrestrial radiation back to the space. This scientific phenomena is known as the “Radiative Forcing”. Because of that, temperature in lower part of the atmosphere (Troposphere) will reduce.
In green house effect, greenhouse gases reflect terrestrial radiation back to the earth’s surface and absorb extraterrestrial radiation. So, we can say without any doubt that, this is the opposite effect of green house effect, the cooling effect.
The same thing can happen again now, because of the large amount of ash and SO2 ejected to the atmosphere from the eruption occurred in Iceland. So this incident could bring back the issue again. But, there is much less chance to get a solution from this scientific phenomena for global warming.