WASHINGTON - April 16 - Volcanic ash from Mt. Eyjafjallajökull in Iceland is disrupting air travel. Could it also disrupt the climate?

The short answer is yes—at least temporarily. When sulfur dioxide from volcanic eruptions enters the second layer of the atmosphere—the stratosphere—it converts into sulfuric acid particles that act like tiny mirrors reflecting sunlight back into space, cooling the planet. The Eyjafjallajökull eruption, however, is still too small to significantly affect the climate, according to the Union of Concerned Scientists (UCS). The amount of cooling depends on the type of material and the amount of time it stays suspended in the atmosphere.

Eyjafjallajökull pales in comparison to past climate-cooling volcanic eruptions. Eyjafiallajokull’s ash has reached a height of 55,000 feet, according to press reports. By contrast, ash from the 1991 Mt. Pinatubo eruption, one of the biggest in the 20th century, reached 78,740 feet. Overall, Pinatubo, which is in the Philippines, ejected 14 to 26 million metric tons of sulfur dioxide that produced a significant global cooling effect for a few years. Following the eruption, this temporary cooling also slowed sea level rise rates temporarily.

Even if a volcanic eruption were big enough to temporarily cool the planet, heat-trapping carbon dioxide from burning fossil fuels and destroying forests would still pose a significant threat, says UCS climate scientist Brenda Ekwurzel.

“Unlike volcanic ash that will leave the atmosphere within a few months or years, carbon dioxide remains there for decades and even centuries,” Ekwurzel said. “Overloading the atmosphere with carbon dioxide has put us on the path toward a long-term warming trend, so we really can’t pin our hopes on occasional volcanic eruptions to solve the problem.”

The short-term cooling effects of the Mt. Pinatubo eruption are long gone, and global warming is continuing unabated, she said. “In fact, we just experienced the hottest decade on record.”

Some scientists are exploring the possibility of mimicking volcanoes by artificially injecting sulfur dioxide into the atmosphere to temporarily cool the planet, which theoretically would give industrialized countries more time to reduce their carbon dioxide emissions. Such schemes should be viewed with caution, Ekwurzel said.

“We’re already conducting a giant experiment with the planet by injecting so much carbon dioxide into the atmosphere,” she said. “It’s not clear that the potential risks of more human tampering with the climate are worth whatever temporary relief this might provide. But the fact that scientists are even contemplating these ideas does highlight how urgent the need to act has become.”

While a quick-fix is appealing, there are serious drawbacks to intervening with a complex climate system. Ekwurzel points out that the ocean is becoming more acidic as it absorbs excess carbon dioxide from the atmosphere, threatening coral reefs and other marine life. Deliberately reflecting sunlight would do nothing to change this and it could have other hard-to-predict effects, such as changing rainfall patterns.

“Climate change isn’t just about the Earth’s thermostat,” she said, “It’s about rapidly shifting our climate in ways we might not even be able to fully anticipate. The prudent thing to do is dramatically reduce our emissions to avoid finding out just how bad climate change could become.”