Volcanic Eruptions and Cooling of the Planet

By Dr. Charles Kironji Gatebe, NASA Scientist for GLOBE Student Research Campaign on Climate

The recent volcanic eruption in Iceland marked by the spectacular “curtain-of-fire” and near-complete shut-down of air travel in Europe in mid-April will probably earn a place in the history books (see pictures of the Icelandic volcano at the Washington Post.)

The thick ash plume and steam can be seen on NASA satellite images over the North Atlantic region. Besides the widespread air travel disruptions that this event has caused throughout Europe, the gases and ash aerosol particles thrown into the atmosphere during the eruptions can warm or cool the earth’s surface, depending on the surface type and properties, and affect weather and climate. The potential long-term impacts of these volcanic emissions on climate may be understood by looking at some of the famous volcanic eruptions of consequence to climate.

Two of the most commonly cited volcanic eruptions in the climate literature are Krakatua (1883; Indonesia) and Mt. Pinatubo (1991; Philippines). The most massive explosions of Krakatua took place in August, 1883, and rank among the most violent volcanic events in recorded history. In the year following the eruption, average global temperatures reportedly fell by as much as 1.2 °C (2.2 °F). Weather patterns continued to be chaotic for years, and temperatures did not return to normal until 1888. The eruption injected an unusually large amount of sulfur dioxide gas high into the stratosphere, which was subsequently transported by high-level winds all over the planet. This led to a global increase in sulfurous acid concentration in high-level cirrus clouds and the clouds became brighter. The increase in cloud reflectivity (or albedo) meant that more incoming light from the sun than usual was reflected back to space, and as a result, the entire planet became cooler, until the suspended sulfur fell to the ground as acid precipitation.

In June 1991, the best-documented explosive volcanic event to date and the second largest volcanic eruption of the twentieth century took place on the island of Luzon in the Philippines, a mere 90 kilometers northwest of the capital city Manila. Up to 800 people were killed and 100,000 became homeless following the Mount Pinatubo eruption, which climaxed with nine hours of eruption on June 15, 1991. On June 15, millions of tons of sulfur dioxide were discharged into the atmosphere, resulting in a decrease in the temperature worldwide over the next few years.

Pinatubo eruption provided scientists with a basis for constructing or modeling the change in Earth’s radiation balance (scientists like to call this change “radiative forcing”) due to explosive volcanoes. It is now well established that volcanic eruptions cause the stratosphere to warm and the annual mean surface and tropospheric temperature decreases during a period of two to three years following a major volcanic eruption. If you are interested in more technical details on how volcanoes affect climate, you can read a very good paper written by Alan Robock. Given that the Icelandic eruption is along a Mid-Ocean ridge and volcanic Hot spot, do you think the gases and aerosols will be of different composition than the Krakatoa and Pinatubo eruptions, which are associated with plate subduction along convergent plate boundaries? If there is a difference, what effect might that have on weather and climate over the next few years?

So the disruption of the air travel by the Iceland’s Eyjafjallajökull Volcanic eruptions is just the beginning; other weather and climatic effects will follow.  In the days and months ahead, we are likely to experience darkened sky and spectacular sunsets in different parts of the world.