Modification du climat / Weather modification

Cloud-seeding may take edge off bad weather

 

OTTAWA — During St. Petersburg’s 300th anniversary celebrations three years ago, Russian President Vladimir Putin ordered 10 cloud-seeding planes into the air, to induce rain about 50 kilometres outside the city. « Our aim is to empty all clouds of rain before they hit the city borders, » the physicist in charge of the project told a reporter.

 
 
 

OTTAWA — During St. Petersburg’s 300th anniversary celebrations three years ago, Russian President Vladimir Putin ordered 10 cloud-seeding planes into the air, to induce rain about 50 kilometres outside the city. « Our aim is to empty all clouds of rain before they hit the city borders, » the physicist in charge of the project told a reporter.

Rain on Putin’s parade would have been a minor inconvenience. In New Orleans, on the other hand, last fall’s rain was nothing short of catastrophic — and with the arrival of this year’s hurricane season, scientists are wondering: if we can change the weather, can we head off hurricanes?

It’s not a new idea. In 1947, researchers from General Electric and the U.S. government used an airplane to « seed » a hurricane 500 kilometres off the coast of North Carolina. The hurricane reversed direction and sped toward Savannah, Georgia, where it caused $2-million damage. The U.S. Department of Defence promptly classified details of the experiment to avoid litigation.

The field of « weather modification » has come a long way since then, but experts still aren’t sure humans can affect something as massive as a hurricane, which can release energy equivalent to a 10-megaton nuclear bomb every 20 minutes, according to the U.S. Hurricane Research Division. A later analysis of the 1947 Georgia hurricane suggested the seeding experiment actually had nothing to do with its sudden change of direction.

In fact, the evidence for cloud-seeding itself, widely used to enhance rainfall or reduce hail damage, is hotly debated.

« The problem is, you never know what you would have got if you hadn’t seeded, » says Terry Krauss, the Red Deer, Alta.-based chief scientist of Weather Modification, Inc.

The North Dakota company has been contracted by a group of insurance companies to seed the clouds in « Hail Alley » between Calgary and Red Deer for the past 10 years, flying about 100 sorties between June 1 and Sept. 15 each year.

Before the program started, Krauss says, the insurance companies were paying about $100 million a year in insurance for hail damage, and a single storm in 1991 cost $400 million. With cloud seeding in place, payouts are down 50 per cent — a handsome return on the $2-million annual investment.

« In spite of the lack of scientific proof-positive, the financial indicators are very good, » Krauss says.

That’s good enough for the insurance companies, who have signed on for another five years. But insurance records aren’t a reliable way to judge a project, since they may be spun for marketing purposes, says George Isaac, a senior scientist with Environment Canada’s cloud physics and severe weather section.

« There’s no hard evidence for hail suppression, » he says. A 2003 report by the U.S. National Research Council agreed, concluding that « there still is no convincing scientific proof of the efficacy of intentional weather modification efforts. »

Pioneered in the 1940s, cloud-seeding involves dropping particles of silver iodide or dry ice into gathering clouds. Raindrops coalesce around the seeds, and — so the theory goes — rain falls. But is it just « borrowing » rain from the next day, or from a neighbouring region? And can the seeds tie up moisture that would otherwise grow into damaging hailstones?

These are the questions that about 100 scientists from around the world were confronting recently in San Antonio, Texas, at the annual meeting of the Weather Modification Association.

« In the semi-arid areas where I live, we’re more interested in increasing the rainfall, » said Tommy Shearer, a Texan who helped organize the conference. Hurricanes are just too big to modify, he said. « The military did that back in the ’60s. They abandoned it, classified it, said never again. »

The U.S. government’s Project Stormfury, an attempt to weaken hurricanes by seeding, actually ran from 1962 all the way to 1983, with ambiguous and ultimately disappointing results.

But others at the meeting, such as Krauss, were more optimistic. The key would be to use today’s more sophisticated weather-tracking satellites and computer-modelling abilities to attack hurricanes before they grow too large to handle.

« You can’t go head to head with a Category 4 or 5, » Krauss said. « But what can you do at an earlier stage? »

This approach has spawned a series of suggestions in recent years, and gained support with an article published in Scientific American in 2004 by Ross Hoffman of Atmospheric and Environmental Research, a research firm in Boston. Hoffman showed that a change of just two or three degrees Celsius near the eye of a hurricane, applied early enough, could radically alter the course of the storm.

« It turns out the very thing that makes forecasting any weather difficult — the atmosphere’s extreme sensitivity to small stimuli — may well be key to achieving the control we seek, » he wrote.

But how to produce that small stimulus? Scientists have proposed a number of ambitious ideas in the last few years.

The U.S. Hurricane Research Division in Florida gets about 120 such proposals a year, and has a form letter to respond to perennial favourites like dropping a nuclear bomb into the heart of the storm, or dragging icebergs from the North Pole to cool the water around a hurricane.

« You give everyone a fair shake, » says Frank Marks, Jr., the division’s director. « As a scientist you’re always questioning everything. »

While some of the ideas, such as floating jet engines in a storm’s path to remove moist air, are considered fairly farfetched, other work such as Hoffman’s is well-respected by Marks and other hurricane experts. The problem, though, is that current hurricane models simply aren’t good enough to make an accurate prediction about what might happen if you heat up a storm with an infrared beam.

« You don’t want to modify something unless you know what the impact will be, » Marks says.

And all of this raises an even bigger question: if we could change hurricanes, would we? « If man in his hubris makes a change, it may be favourable to me, but it may not be favourable to someone upstream or downstream from me, » Marks says.

Isaac at Environment Canada has dealt with irate farmers who worry that the hail-suppression project in Alberta is causing drought in other parts of the province. He doesn’t know whether the claims are true, and if he did, he’s not sure how the dispute could be resolved. « It’s a difficult question, not handled easily, » he says.

Given the carnage wrought by last year’s record 28 hurricanes, it’s tempting to think that the benefits would outweigh the risks. But those considering undertaking the challenge should bear in mind an episode from weather modification’s early, less reputable history.

In 1915, San Diego city council offered Charles Hatfield $10,000 if he could attract enough rain to fill a large reservoir, using his patented mixture of 23 chemicals. Hatfield built his contraption, and sure enough, the rain started. It filled the reservoir, and kept raining, eventually bursting a dam and killing 20.

In court cases that stretched on for more than two decades, Hatfield was able to avoid being held liable for the $3.5 million in damages caused by the flood. But he never did get his $10,000.

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