Maverick Climate Scheme Gets Reality Check

Aug. 15, 2007 — Emulating the sun-dimming effects of large volcanic eruptions to slow the Earth's greenhouse effect, as some have proposed, may just make matters worse, say scientists studying the effects of nature's recent volcanics.

The eruption of the Philippine's Mount Pinatubo in 1991 shows that the far-flung effects of its sun-blocking particles led to a marked decrease in precipitation worldwide.

An attempt to mimic volcanoes to cool the Earth by blocking solar energy reaching the Earth's surface could have similar short-term effects — which could be worse than global warming.

"They're all designed to cut the incoming (solar) radiation," said climate researcher Kevin Trenberth, referring to various proposals to "geo-engineer" our way out of global warming. But you can't engineer the climate without thinking about the entire flow of that incoming heat, he added.

That heat flow warms tropical oceans, which evaporates lots of water. The water vapor moves to higher latitudes, where it rains down and releases heat that can radiate back into space.

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"So if you are changing this flow of energy," said Trenberth, who works at the National Center for Atmospheric Research (NCAR), "it's going to have an impact."

The immediate effect is less rain falling worldwide. In other words: drought.

Trenberth and his NCAR colleague Aiguo Dai found just such a pronounced drop in precipitation — seen in terms of the world's stream and river flows — after the 1991 eruption of Mount Pinatubo.

There was a "singular decrease" in river discharges into the oceans, Trenberth told Discovery News. The researchers' work is published in the latest issue of Geophysical Research Letters.

Unlike the more gradual effects of global warming, droughts have been known to cause immediate famines along with political and economic instability.

"There is really a major ethical aspect to it," said Trenberth. "If you can really [dim solar radiation], who is in charge? Who plays God?" After all, he said, it's one thing to accidentally cause the climate to change, as has happened with global warming, and another to deliberately tinker with it.

"Any time you are talking about geo-engineering you have to be very careful," said climate researcher Robert Adler of NASA's Goddard Space Flight Center. "If you don't understand the system — and we do not fully understand this system — you can get perturbations."

Another problem with mimicking volcanoes is that you have to keep doing it or face potential trouble when the effect wears off in 18 months or so and the climate rebounds, said Trenberth.

The National Center for Atmospheric Research

NASA on volcanoes and climate change.

Explore a virtual volcano.

All about volcanoes from the USGS.