The climatic aftermath. (Perspectives: Pinatubo eruption)

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Author: Alan Robock
Date: Feb. 15, 2002
From: Science(Vol. 295, Issue 5558)
Publisher: American Association for the Advancement of Science
Document Type: Article
Length: 1,330 words

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The eruption of Mount Pinatubo on Luzon Island, Philippines (15.1 [degrees] N, 120.4 [degrees] E), on 15 June 1991 produced the largest stratospheric volcanic aerosol cloud of the 20th century (1). In just a few days, about 20 megatons of S[O.sub.2] was injected into the stratosphere (1). The effect of the eruption on global climate could be felt for years. Surface air temperatures over Northern Hemisphere (NH) continents were cooler than normal by up to 2 [degrees] C in the summer of 1992 and warmer than normal by up to 3 [degrees] C in the winters of 1991-92 (see the figure) and 1992-93.

A recent conference (2) highlighted the intense research activity in the 10 years since the eruption. From ozone destruction to global changes in atmospheric circulation, the impacts of explosive volcanic eruptions on weather and climate have been elucidated (3). Insights into the effects of volcanic eruptions on surface temperatures have helped attribute the warming of the past century to anthropogenic greenhouse gas emissions. Better seasonal forecasts should be possible after the next major eruption.

In the 2 years after the Pinatubo eruption, data from the Total Ozone Mapping Spectrometer (TOMS) and other sources showed unusual [O.sub.3] decreases at mid-latitudes and NH high latitudes (4-7). Column [O.sub.3] was reduced by about 5% in mid-latitudes (4-6). The ozone was destroyed by the same mechanism that causes the ozone hole over Antarctica in October each year. Sulfate aerosols produced by Pinatubo and injected into the lower stratosphere provided surfaces for heterogeneous reactions revolving anthropogenic chlorine, leading to the chemical destruction of [O.sub.3] (8-10).

Like the ozone hole, ozone depletion by volcanic aerosols is a recent phenomenon. It is caused by elevated chlorine concentrations in the stratosphere, which only appeared in the last couple of decades because of anthropogenic emissions and will hopefully disappear in a few decades as emissions are increasingly regulated. A lower ozone concentration causes less ultraviolet (UV) absorption in stratosphere. Some UV radiation is backscattered by the aerosols, but...

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Gale Document Number: GALE|A83450700