The argument that human-caused carbon emissions(排放) are merely a drop in the bucket compared to greenhouse gases generated by volcanoes has been making its way around the rumor mill for years. And while it seems to be reasonable, the science just doesn't back it up.
According to the US Geological Survey (USGS), the world's volcanoes, both on land and undersea, generate about 200 million tons of carbon dioxide (CO2) annually, while our automotive and industrial activities cause some 24 billion tons of CO2 emissions every year worldwide. Despite the arguments to the contrary, the facts speak for themselves: Greenhouse gas emissions from volcanoes compose less than one percent of those generated by today's human activities.
Another indication that human emissions surpass those of volcanoes is the fact that atmospheric CO2 levels as measured by sampling stations around the world, have gone up consistently year after year regardless of whether or not there have been major volcanic eruptions in specific years. "If it were true that individual volcanic eruptions dominated human emissions and were causing the rise in carbon dioxide concentrations, then these carbon dioxide records would be full of spikes —one for each eruption," says Coby Beck, a journalist writing for online environmental news. "Instead, such records show a smooth and regular trend."
Furthermore, some scientists believe that volcanic eruptions, like that of Mt.St. Helens in 1980 and Mt. Pinatubo in 1991, actually lead to short-term global cooling, not warming, as sulfur dioxide (SO2), ash and other particles in the air and stratosphere(平流层) reflect some solar energy instead of letting it into Earth's atmosphere. SO2, which converts to sulfuric acid aerosol, when it hits the stratosphere, can linger there for as long as seven years and can exercise a cooling effect long after a volcanic eruption has taken place.
Scientists tracking the effects of the major 1991 eruption of the Philippines' Mt. Pinatubo found that the overall effect of the blast was to cool the surface of the Earth globally by some 0.5 degrees Celsius a year later, even though rising human greenhouse gas emissions and an El Nino event caused some surface warming during the 1991-1993 study period.
In an interesting twist on the issue, British researchers last year published an article in the peer reviewed scientific journal Nature showing how volcanic activity may be contributing to the melting of ice caps in Antarctica but not because of any emissions, natural or man-made. Instead, scientists Hugh Corr and David Vaughan of the British Antarctic Survey believe that volcanoes underneath Antarctica may be melting the continents ice sheets from below, just as warming air temperatures from human-induced emissions erode them from above.
