Indonesia’s Mount Agung inflamed up a notch last weekend when a much larger ash cloud shot into the atmosphere and lava made its way to the surface.  

If it proceeds to a major eruption, the effects on the climate could be fairly substantial. The main effect on weather near a volcano results in rain, lightning, and thunder during eruption. This is because all the ash particles that are thrown up into the atmosphere are good at attracting or collecting water droplets. The reason is not yet known exactly how the lightning is caused but it probably involves the particles moving through the air and separating positively and negatively charged particles.

The gases and dust particles thrown into the atmosphere during volcanic eruptions will have impacts on climate. Most of the particles ejected from volcanoes will cool the surface by shading incoming solar radiation. The cooling effect can last for months to years depending on the characteristics of the eruption.

Volcanoes have also caused global warming over millions of years during times in Earth’s history when extreme amounts of volcanism occurred, releasing greenhouse gases into the atmosphere.

On longer time scales, eruptions can inject massive quantities of ash into the atmosphere, greatly reducing the solar heating of the Earth and potentially interrupting the food supply for several years.

Although volcanic activity is at a specific place, its effects can be more widely distributed through gases, dust and ash, which 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 impacted the hemisphere where these are located.

As for the worldwide effects of volcanic eruptions this only happens when there are large explosive eruptions that throw material into the stratosphere. If it only gets into the troposphere it gets flushed out by rain.

The effects on the climate haven’t been completely figured out yet but it seems to depend on the size of the particles (again mostly droplets of sulfuric acid). If they are big then they let sunlight in but don’t let heat radiated from the Earth’s surface out, and the net result is a warmer Earth (the famous Greenhouse effect). If the particles are smaller than about 2 microns then they block some of the incoming energy from the Sun and the Earth cools off a little. That seems to have been the effect of the Pinatubo eruption where about a 1/2 degree of cooling was noticed around the world. Of course that doesn’t just mean that things are cooler, but there are all kinds of effects on the wind circulation and where storms occur.

Scientifically speaking, the volcanic eruption will have impact on environment by following means.

Volcanoes also release large amounts of greenhouse gases such as water vapor and carbon dioxide. The amounts put into the atmosphere from a large eruption doesn't change the global amounts of these gases very much. However, there have been times during Earth history when intense volcanism has significantly increased the amount of carbon dioxide in the atmosphere and caused global warming. In fact, volcanism produces about 3 percent of the total CO2 with the other 97 percent coming from anthropogenic sources.

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. But the smallest particles of dust get into the stratosphere and are able to travel vast distances, often worldwide. These tiny particles are so light that they can stay in the stratosphere for months, blocking sunlight and causing cooling over large areas of the Earth.

Often, erupting volcanoes emit sulfur dioxide into the atmosphere. Sulfur dioxide is much more effective than ash particles at cooling the climate. The sulfur dioxide moves into the stratosphere and combines with water to form sulfuric acid aerosols. The sulfuric acid makes a haze of tiny droplets in the stratosphere that reflects incoming solar radiation, causing cooling of the Earth’s surface. The aerosols can stay in the stratosphere for up to three years, moved around by winds and causing significant cooling worldwide. Eventually, the droplets grow large enough to fall to Earth.

Dr. Muhammad Irfan Khan is Professor of Environmental Science Department of Environmental Science International Islamic University, Islamabad, Pakistan.