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The 1991 eruption of Mt. Pinatubo injected sufficient amounts of sulfur into the atmosphere to cool the earth by 0.9°F for over a year

Summary​

The 1991 Mount Pinatubo eruption released 20 million tons of sulfur dioxide into the stratosphere, forming aerosols that cooled global temperatures by 0.9°F – 1.08°F for about a year. This event demonstrated stratospheric aerosol injection's climate effects, including ozone layer depletion through chemical reactions and altered precipitation patterns. While regional agriculture suffered lasting damage from ashfall, global crop impacts revealed complex interactions involving scattered sunlight, CO₂ absorption, and UV exposure. The eruption's mixed effects on photosynthesis and ozone highlight both potential benefits and risks of geoengineering strategies. Climate effects gradually diminished over three years as aerosols dissipated.

In June 1991, the catastrophic eruption of Mount Pinatubo in the Philippines ejected approximately 10 cubic kilometers of volcanic material, including ash and pumice, and 20 million tons of sulfur dioxide (SO₂) into the stratosphere. This SO₂ reacted with the atmosphere to form sulfuric acid aerosols which scattered incoming sunlight back out into space, reducing the amount of solar radiation that reached the Earth's surface.

The eruption of Mount Pinatubo was the second most powerful volcanic eruption of the 20th century, after the 1980 eruption of Mount St. Helens in the United States. The eruption had a significant impact on global climate, causing temperatures to drop by up to 0.9°F – 1.08°F in the northern hemisphere, and up to 0.72°F in large parts of the southern hemisphere 1.

The cooling effect of the Mount Pinatubo eruption remained consistent for one year, after which the concentration of sulfate particles began to decrease, returning to pre-eruption levels by the end of the third year 1.

The eruption of Mt Pinatubo also had a significant impact on the the earths ozone layer. Sulfate aerosols provide a surface for chlorine, which is is found in high concentrations in the atmosphere due to human activities, to react with ozone, leading to its depletion by close to 2% – 3% 1 2.

The drastic change to the levels of incoming solar radiation also had significant effects on global precipitation patterns which are heavily influenced by water condensation. Following the eruption, there was an observable reduction in overland precipitation, and a record reduction in land based water discharge into the ocean 3.

The impact of Mt Pinatubo on global agriculture is more complicated. On a regional level, local crops such as rice saw reduction in yields that persisted for over a decade due to ash fall 4. However, the effect on global crop production is not as well understood. The inclusion of solar radiation may reduce heat stress on plants allowing for greater productivity, which is becoming more significant as the global climate warms 5. But damage to the zone layer can allow for more damaging ultraviolet light to reach crops, thus reducing yields 6. Global crop yields can also be effected by how they receive scattered light. Following the eruption of Mt Pinatubo, there was a noticeable drop in global CO₂ levels which have been linked to increase levels of photosynthesis that is attained by a less indirect light path reaching parts of plants that would not have occurred from un-scattered light 7.

The eruption of Mount Pinatubo in 1991 is one of the most significant volcanic events in recent history and has played a crucial role in shaping our understanding of Stratospheric Aerosol Injection (SAI) as a geoengineering strategy. The eruption provided a natural experiment for observing the effects of injecting large amounts of aerosols into the stratosphere, leading to a temporary cooling of the Earth's climate. However, using this event as a basis for understanding SAI also comes with limitations and uncertainties.

Sources​

Footnotes​

  1. Self, S., Zhao, J.-X., Holasek, R. E., Torres, R. C., & King, A. J. (1993). The atmospheric impact of the 1991 Mount Pinatubo eruption (NASA Report No. 19990021520). NASA Goddard Space Flight Center. https://ntrs.nasa.gov/citations/19990021520 ↩ ↩2 ↩3

  2. Crutzen, P. J. (2006). Albedo enhancement by stratospheric sulfur injections: A contribution to resolve a policy dilemma? Climatic Change, 77(3-4), 211-220. https://doi.org/10.1007/s10584-006-9101-y ↩

  3. Robock, A., Oman, L., & Stenchikov, G. L. (2007). Regional climate responses to geoengineering with tropical and Arctic SO₂ injections. Geophysical Research Letters, 34, L19702. https://doi.org/10.1029/2007GL030524 ↩

  4. Lebon, S. L. G. (2009). Volcanic activity and environment: Impacts on agriculture and use of geological data to improve recovery processes [Master's thesis, University of Iceland]. https://skemman.is/bitstream/1946/3303/1/Sylviane_Lebon_fixed.pdf ↩

  5. Pongratz, J., Lobell, D., Cao, L., & Caldeira, K. (2012). Crop yields in a geoengineered climate. Nature Climate Change, 2(2), 101-105. https://doi.org/10.1038/nclimate1373 ↩

  6. Proctor, J., Hsiang, S., Burney, J. et al. Estimating global agricultural effects of geoengineering using volcanic eruptions. Nature 560, 480–483 (2018). https://doi.org/10.1038/s41586-018-0417-3 ↩

  7. Gu, L., Baldocchi, D. D., Wofsy, S. C., Munger, J. W., Michalsky, J. J., Urbanski, S. P., & Boden, T. A. (2003). Response of a deciduous forest to the Mount Pinatubo eruption: Enhanced photosynthesis. Science, 299(5615), 2035-2038. http://www.jstor.org/stable/3833713 ↩