Tinkering with clouds

On Sept. 11, 1992, hurricane Iniki slammed into the Hawaiian island of Kauai, packing winds gusting up to 175 m.p.h.

The storm inflicted an estimated $2 billion in damage and 105 casualties, damaged or destroyed 10,000 homes and businesses, and left once-lush tropical mountainsides looking as though they'd been mowed by a giant weed-whacker.

Ross Hoffman, an atmospheric scientist, looks back on the tragedy and asks a daring question: What might it have taken to nudge the hurricane's track 70 miles farther west - just enough to avoid the damage and casualties the storm left in its wake?

Over the past two decades, the idea of modifying large-scale storms such as hurricanes has lain dormant, following 20 years of inconclusive research. Now, however, a small group of atmospheric scientists is giving the concept a fresh look.

Armed with a deeper understanding of how the storms and atmosphere work and with more

sophisticated tools to measure and model atmospheric conditions, these scientists are seeking to move from Mark Twain's lament that no one does anything about the weather toward science-fiction writer Arthur C. Clarke's vision of modifying weather for humanity's benefit.

It is a long-term vision, acknowledges Dr. Hoffman, a vice president with Atmospheric and Environmental Research, Inc., a research and consulting firm in Lexington, Mass. Tugging on a hurricane's atmospheric reins is at least 30 to 40 years away, he estimates.

Others, such as Massachusetts Institute of Technology atmospheric scientist Kerry Emanuel, suggest such capabilities are "perhaps 100 years out."

"Before we can really control weather," Hoffman says, "we have to be able to observe the weather and forecast the weather much better than we do now."

More broadly, he adds, society must grapple with an increasingly common question as science places in human hands the ability to manipulate a range of physical processes at their most fundamental levels: "Even if we can do this, is this something we really want to do?"

Indeed, humans have been modifying weather inadvertently as well as intentionally for decades.

For example, researchers in 1998 and 1999 looked at the impact of air pollution over the Indian Ocean. They found an unexpectedly large amount of pollution, including dark soot and the much tinier dark aerosols, over the northern Indian Ocean. The soot came from burning coal and wood and from inefficiently burned diesel fuel on the Indian subcontinent. Researchers discovered that the soot and dark aerosols reradiated heat from the sun, drying out the surrounding air and suppressing cloud formation.

Meanwhile, according to the United Nations' World Meteorological Organization (WMO), at least 25 countries are engaged in weather modification projects to enhance rain and snowfall, or suppress hail. In the United States, 12 states have had weather modification programs. Texas runs a program at the county level for rain enhancement, while North Dakota is focusing on hail suppression.

These efforts have grown out of research dating back to the late 1940s, when scientists first discovered that dry ice and silver iodide particles could act as seeds to stimulate droplet formation in clouds.

While the concept has been easy to demonstrate in the lab, meeting the same level of scientific proof in the field has been more difficult.

A range of studies over the years has cast doubts on cloud-seeding techniques (see chart above), especially the use of dry ice particles.

Natural variability in clouds and rainfall make it hard to verify scientifically if seeding is having any affect, says Brant Foote, director of the research applications program at the National Center for Atmospheric Research in Boulder, Colo.

Researchers seeded hurricanes in a 20-year federal research project dubbed Project Storm Fury. Scientists were testing the idea that seeding could be used to take some of the punch out of hurricanes before they made landfall. But the program foundered on inconclusive results.

Page: 1 | 2