The eruption of Eyjafjallajokull in Iceland could mean some good news for those of us concerned with understanding the science of climate change.
As volcanoes go, this is small stuff. The last volcano to have a substantial effect on global climate was Mount Pinatubo which erupted in the Philippines in 1991. Volcanoes affect global climate largely because the sulfur gases that they emit oxidize in the atmosphere to form sulfate aerosols (fine particulate matter), which stay around in the stratosphere for at least 12 months, and act as a strong cooling agent. According to the National Oceanic and Atmospheric Administration (NOAA), Mt. Pinatubo caused global temperatures to dip by about 0.5 degrees Centigrade for a year. The ash, which has been of concern to airline passengers in Europe and many others across the globe recently, generally has only a small and local effect on climate –it tends to fall to earth in a matter of weeks.
Can we therefore, safely conclude that this latest disruption can be ignored (unless we were planning to take a flight in the past week)? I think that the answer should be “no”, although the benefit to climate science is a very indirect one.
The combined effect of all aerosols on global climate is very large, consisting of complex positive and negative impacts on warming. Sulfate aerosols from volcanoes are a natural phenomenon, but human activities generate large quantities of aerosols that are similar to volcanic ash. Black carbon (soot) is a strong warming agent, while other aerosols such as organic carbon and dust can cool by reflection.
Apart from warming the atmosphere directly by absorbing heat, carbon aerosols that land on ice and snow cause more rapid melting. When white snow and ice melt, they expose earth or sea that is darker. The darker surfaces reflect less heat into space and this exacerbates global warming.
Scientists have been studying the trajectory of smoke from cooking fires in India as it makes its way onto Himalayan glaciers, accelerating melting. Any smoke in Northern Canada, Russia and Europe is also of major concern because some particulates end up on the surface of the Arctic.
Despite their importance to global climate, aerosols remain perhaps the least understood part of the climate system. There seems to be a lack of accurate observations and measurements of their prevalence, and insufficient understanding of their short term atmospheric and chemical dynamics. As the 2007 IPCC report stated: “The total direct radiative forcing [of aerosols] as derived from models and observations is estimated to be -0.5 [+/-0.4] W per square meter, with a medium-low level of scientific understanding.” By contrast, for the greenhouse gases, IPCC states that the scientific understanding of forcing is “high”.
Perhaps this will change with more attention on the inadequacies of observations and understanding of volcanic ash. The basic issues for the ash are the same as for other aerosols that affect climate. The Daily Telegraph reported (April 20) that the model used by "hapless forecasters"in the UK’s Volcanic Ash Advisory Center was first devised in the wake of the Chernobyl nuclear disaster in 1986. The model “calculates the direction, speed, height and density of any particles that travel in the air – be they from an industrial accident or a volcano”.
From being the poor cousin of Greenhouse Gases, relegated to specialized academic journals, aerosols, in the form of volcanic ash, are now front page news. The Washington Post reported (April 21) that a National Weather Service scientist told reporters that “Volcanic ash science still has many limitations”. For “volcanic ash” read “aerosols”.
Perhaps an indirect consequence of a small volcano eruption in Iceland will be to fund a lot more basic research into the behavior of aerosols in the atmosphere. Improved models used to reduce inconvenience to air passengers may soon also improve our ability to understand how fires and diesel engines are impacting climate directly and accelerating the melting of glaciers.
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