delanceyplace.com 4/21/10 - volcanos and global cooling

In today's excerpt - massive volcano eruptions have caused the temperature of the earth to cool significantly by blocking light from the sun:

"The connection between volcanoes and climate is hardly a new idea. ... Benjamin Franklin, wrote what seems to be the first scientific paper on the topic. In 'Meteorological Imaginations and Conjectures,' published in 1784, Franklin posited that recent volcanic eruptions in Iceland had caused a particularly harsh winter and a cool summer with 'constant fog over all Europe, and [a] great part of North America.' In 1815, the gargantuan eruption of Mount Tambora in Indonesia produced 'The Year Without a Summer,' a worldwide disaster that killed crops, prompted widespread starvation and food riots, and brought snow to New England as late as June.

"As Nathan Myhrvold [of Intellectual Ventures and formerly of Microsoft] puts it: 'All really big-ass volcanoes have some climate effects.'

"Volcanoes erupt all the time, all over the world, but truly 'big-ass' ones are rare. If they weren't - well, we probably wouldn't be around to worry about global warming. The anthropologist Stanley Ambrose has argued that a supervolcanic explosion at Lake Toba on Sumatra, roughly seventy thousand years ago, blocked the sun so badly that it triggered an ice age that nearly wiped out Homo sapiens. What distinguishes a big-ass volcano isn't just how much stuff it ejaculates, but where the ejaculate goes. The typical volcano sends sulfur dioxide into the troposphere, the atmospheric layer closest to the earth's surface. This is similar to what a coal-burning power plant does with its sulfur emissions. In both cases, the gas stays in the sky only a week or so before falling back to the ground as acid rain, generally within a few hundred miles of its origin.

"But a big volcano shoots sulfur dioxide far higher, into the stratosphere. That's the layer that begins at about seven miles above the earth's surface, or six miles at the poles. Above that threshold altitude, there is a drastic change in a variety of atmospheric phenomena. The sulfur dioxide, rather than quickly returning to the earth's surface, absorbs stratospheric water vapor and forms an aerosol cloud that circulates rapidly, blanketing most of the globe. In the stratosphere, sulfur dioxide can linger for a year or more, and will thereby affect the global climate.

"That's what happened in 1991 when Mount Pinatubo erupted in the Philippines. Pinatubo made Mount St. Helens look like a hiccup; it put more sulfur dioxide into the stratosphere than any volcano since Krakatoa, more than a century earlier. In the period between those two eruptions, the state of science had progressed considerably. A worldwide cadre of scientists was on watch at Pinatubo, equipped with modern technology to capture every measurable piece of data. The atmospheric aftereffects of Pinatubo were undeniable: a decrease in ozone, more diffuse sunlight, and, yes, a sustained drop in global temperature."

Author: Steven D. Levitt and Stephen J. Dubner

Title: Superfreakonomics

Publisher: HarperCollins

Date: Copyright 2009 by Steven D. Levitt and Stephen J. Dubner

Pages: 189-190