5.0 Climate Impacts

Large volcanic eruptions impact climate on a range of timescales. This section discusses the known climate impacts as shown by observed data from recent large eruptions and modeled results from General Circulation Models (GCMs) simulating their effects. First, we will examine the radiative properties of a volcanic ash cloud. Then, we will look at Earth’s climate response to radiative changes caused by the cloud.

Since 1960, several explosive eruptions have provided significant data to better understand the effects of volcanic ash and gases on climate. Four eruptions in particular have been extensively studied: Agung (Indonesia, 1963), Mt. St. Helens (U.S., 1980), El Chichón (Mexico, 1982), and Mt. Pinatubo (Philippines, 1991). The data from these eruptions, collected from ever-improving satellites and volcanic observation networks, combined with the increasing sophistication of coupled atmosphere/ocean GCMs have given climate scientists a wealth of tools to diagnose a volcano’s climate impact.


Global average surface temperature change with volcanic eruptions

Study the image above. What effects do large volcanic eruptions seem to have on Earth’s globally-averaged surface temperature? Complete the sentence below.

Large volcanic eruptions release ash and gases _____. (Choose the best answer.)

The correct answer is b).

Large volcanic eruptions can cool Earth by injecting ash, gases, and water vapor into the stratosphere. The size of an eruption will determine the degree a volcano impacts climate.

To affect climate an eruption must:

  1. produce significant quantities of gaseous sulfur compounds
  2. inject this sulfur well into the stratosphere

Only large eruptions, approximately those as big or bigger than Pinatubo in the picture below, release enough sulfur into the stratosphere to have a significant effect (i.e., causing a globally-averaged cooling of 1/2°C or more). The resulting haze shades the sun for one to many years after each major blast, depending on the eruption size.

A chart showing the relative sizes of 7 eruptions: Yellowstone is the biggest, Recent eruptions are the smallest in terms of volume of material expelled to the surface.

A size comparison of seven well-known volcanic eruptions shown as volume of material expelled to the surface. The Yellowstone caldera eruption was the largest. Recent eruptions of Puyehue Cordón-Caulle and Eyjafjallajökull have been much smaller.

Let’s consider the processes through which large explosive eruptions influence Earth’s climate.