We all have read about those wacky
atmospheric scientists who wanted to know how much methane in the
atmosphere came from ruminants, that is, cattle, goats, sheep,
buffalo and the like. It made wonderful derisive news for
politicians, comedians, pundits, late-night talk-show hosts, editors
and other evil-doers, bent on tickling the fancy of an
all-too-easy-to-fool public. "Governments spend millions to study
cow farts," read the headlines.
At times, I thought I was the only
person on the planet interested in the outcome. In case you've
forgotten the results (!), the best guess as to methane's role in
global warming is 15 - 18% of the effect.
Methane is about 21 times as potent a
greenhouse gas as is carbon dioxide. Ruminant livestock produce 80
million tons of methane annually, which is about 22% of global
methane emissions from human endeavors. So imagine my surprise upon
learning that methane from geologic sources is not as well known as
Researchers Giuseppe Etiope and
Alexei Milkov have quantified one of the missing methane sources -
mud volcanoes. Worldwide, there are more than 900 mud volcanoes in
26 countries, with 300 more on shallow ocean shelves and many others
uncounted. These volcanoes can be less than 3-ft to more than
As reported in the June issue of
Geology , the two scientists measured the methane output of a
mud volcano in eastern Azerbaijan. It turns out that these mud
volcanoes produce up to 6 to 10 million tonnes of methane per year
into the atmosphere. Worldwide, they emit up to 25% of the annual
geologic methane input to the atmosphere.
Why geologic sources of methane have
not been included in the foremost climate change models? It's
"basically a lack of multidisciplinary climate studies," says Etiope.
Their contribution could have enormous implications for climate
Etiope is a geologist at the National
Institute of Geophysics and Volcanology in Rome. Milkov is a
geologist with BP in Houston.