The aftermath of Hurricane Katrina
The scientific briefing with Luke Boulter
In the last decade very few natural occurrences have shaken the world in the way Hurricane Katrina has. In a matter of hours it reduced an affluent and popular city to nothing more than a quivering shanty town. We saw first hand the power of nature and the panic it can instil even in the wealthiest of countries.
America is currently in the midst of their hurricane season and, despite the most advanced predications, it is never certain whether a hurricane will devastate a coast line, or just fizzle out as it edges towards land, as we saw with Hurricaine Rita two weeks ago. Storms give no clue to what they are doing or where their final end will lie – But America is bracing itself non the less.
The most troubling issue however is not where or when a storm will climax, it is the force in which they do so. Since the 1970s category four and five storms have nearly doubled; Peter Webster of the Georgia Institute of Technology, Atlanta, suggests that this global trend has occurred over the last couple of decades and is directly tied with an increase in global sea temperatures. “We can say with confidence that the trends in sea surface temperatures and hurricane intensity are connected to climate change”, says Judy Curry, also of the Georgia Institute of Technology. Their team looked at the incidence of intense tropical storms with the results showing the strongest affirmation yet that Katrina-level hurricanes are becoming more frequent in our ever warming world. The study shows there has been no general increase in the total number of hurricanes but the proportion of hurricanes reaching categories four or five – with wind speeds above 56 metres per second has risen from 20 per cent in the ’70s to 35 per cent in the past decade.
Hurricanes form when ocean temperatures rise above 26 degrees centigrade. The fuel for hurricanes is water vapour evaporating from the ocean surface; it condenses in the air and releases heat, driving the hurricane. It has been suggested that without an increase in sea surface temperature, Hurricane Katrina would have only reached a category two to three size and would have been incapable of causing the destruction it did.
With the ever increasing death toll from Katrina, people at risk are demanding intervention. Global warming has caused the weather to become increasingly dramatic: if it is too late to prevent these storms, what can be done to halt their destruction? Ultimately can humanity thwart nature?
Enter the scientists: Hurricanes become most devastating when they hit land, so it is suggested that if we prevent them doing this or change where they hit then we can remove the mass devastation that results. This may take some time however, we would be tampering directly with a weather system and that has never been done before.
In April 2005, Moshe Alamaro at the Massachusetts Institute of Technology outlined a plan to use an array of floating jet engines to trigger miniature cyclones in the atmosphere ahead of a hurricane. The idea is to drain the ocean and atmosphere of energy before the hurricane arrives. Critics point out however that even a large array of jet engines probably cannot inject enough energy into the atmosphere to trigger even a tiny storm. Another strategy is to cover the ocean ahead of the hurricane with a thin layer of fish oil that disrupts the flow of energy into the atmosphere. But experiments in 2002 by Kerry Emanuel, a hurricane expert also at MIT, suggest that high winds would break up the oil layer and prevent it from having any effect.
Then there is the idea of triggering storms with soot providing a nucleus for moisture in a cloud to form. In 1973, William Gray, a hurricane expert at Colorado State University, suggested that the extra energy absorbed by soot could trigger smaller storms. In 1958, the US Naval Research Laboratory carried out a series of experiments to monitor clouds seeded with soot but the results were inconclusive.
So, as yet, preventing the hurricane is a no-go - Emanuel has another suggestion however. His idea is to exploit the chaotic features of weather systems, steering them away from populated centres, an idea put forward by Ross Hoffman, a researcher from Atmospheric and Environmental Research, Massachusetts. The idea is based on the so-called butterfly effect. If a chaotic system such as a hurricane is given a small nudge, the nudge is amplified and could end up having enough influence to knock a hurricane off course, almost steering the hurricane clear of heavily populated areas.
Meteorologists first need better hurricane measurements and models to forecast the effect of any ‘nudge’. They also need a way to do the nudging, possibly with space-based reflectors to heat up the atmosphere, something that Hoffman believes is a long way off.
But nudge a hurricane and the danger is that scientists may get blamed and sued wherever it goes. Kerry Emanuel observes “Choosing between a Category three hitting Pensacola and a Category five hitting New Orleans is easy. But the people of Pensacola may have something to say about it.”
Either way, if the people of Pensacola are going to sue, they have a while to complete their closing statements, all of these ideas are theories, and nobody is close to putting them in practice. The question that does face us though is more pertinent now then ever before: are these hurricanes anomalies, or was Katrina the harbinger of a global warming weather system?
