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.
The characteristics of the ash cloud largely determine whether an volcanic eruption influences the climate or not. One important factor is how high it reaches in the atmosphere, Prof Richard Allan , professor of climate science at the University of Reading, tells Carbon Brief:.
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. The extent to which this occurs is an ongoing debate. Sulfuric gases convert to sulfate aerosols, sub-micron droplets containing about 75 percent sulfuric acid. Following eruptions, these aerosol particles can linger as long as three to four years in the stratosphere.
The research team ran a general circulation model developed at the Max Planck Institute with and without Pinatubo aerosols for the two years following the Pinatubo eruption. Volcanic ash, like this from Mount St. Helens, is not really ash, but tiny jagged particles of rock and glass.
It shows that volcanic aerosols force fundamental climate mechanisms that play an important role in the global change process. 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. Most of the particles spewed from volcanoes cool the planet by shading incoming solar radiation. The cooling effect can last for months to years depending on the characteristics of the eruption. Even though volcanoes are in specific places on Earth, their effects can be more widely distributed as gases, dust, and ash get into the atmosphere.
Because of atmospheric circulation patterns, eruptions in the tropics can have an effect on the climate in both hemispheres while eruptions at mid or high latitudes only have impact the hemisphere they are within. Below is an overview of materials that make their way from volcanic eruptions into the atmosphere: particles of dust and ash, sulfur dioxide, and greenhouse gases like water vapor and carbon dioxide.
Volcanic ash or dust released into the atmosphere during an eruption shade sunlight and cause temporary cooling. Larger particles of ash have little effect because they fall out of the air quickly. Small ash particles form a dark cloud in the troposphere that shades and cools the area directly below. Most of these particles fall out of the atmosphere within rain a few hours or days after an eruption.
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