Global climate change, prior to the 20
th
century, appears to have been initiated primarily by major changes in volcanic activity. Sulfur dioxide (SO
2
) is the most voluminous chemically active gas emitted by volcanoes and is readily oxidized to sulfuric acid normally within weeks. But trace amounts of SO
2
exert significant influence on climate. All major historic volcanic eruptions have formed sulfuric acid aerosols in the lower stratosphere that cooled the earth's surface ~0.5
o
C for typically three years. While such events are currently happening once every 80 years, there are times in geologic history when they occurred every few to a dozen years. These were times when the earth was cooled incrementally into major ice ages. There have also been dozens of times during the past 46,000 years when major volcanic eruptions occurred every year or two or even several times per year for decades. Each of these times was contemporaneous with very rapid global warming. Large volumes of SO
2
erupted frequently overdrive the oxidizing capacity of the atmosphere resulting in very rapid warming. Such warming and associated acid rain becomes extreme when millions of cubic kilometers of basalt are erupted in much less than one million years. These are the times of the greatest mass extinctions. When major volcanic eruptions do not occur for decades to hundreds of years, the atmosphere can oxidize all pollutants, leading to a very thin atmosphere, global cooling and decadal drought. Prior to the 20th century, increases in atmospheric CO
2
followed increases in temperature initiated by changes in SO
2
.
By 1962, man burning fossil fuels was adding SO
2
to the atmosphere at a rate equivalent to one "large" volcanic eruption each 1.7 years. SO
2
is playing a far more active role in global warming than recognized by the Intergovernmental Panel on Climate Change. But man is also adding two to three orders of magnitude more CO
2
per year to the climate than one "large" volcanic eruption added in the past. Thus CO
2
, a greenhouse gas, is now also causing warming. Both SO
2
and CO
2
must be reduced to reduce global warming. We have already significantly reduced SO
2
emissions in order to reduce acid rain. We know how to do it both technically and politically.
In the past, sudden climate change was typically triggered by sudden increases in volcanic activity. Slow increases in greenhouse gases, therefore, do not appear as likely as currently thought to trigger tipping points where the climate suddenly changes.
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Global Climate Change
Sulfur Dioxide Initiates Global Climate Change in Four Ways
Abstract for paper submitted for publication November 3, 2008