It's an ill wind of climate change

J MARSHALL SHEPHERD
Last updated 11:49 14/11/2012
Hurricane Sandy
Nasa
Hurricane Sandy hurtled its way along the Gulf Stream from the Caribbean to New York.

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OPINION: In the waning weeks of the North American hurricane season - a time when a superstorm is not expected to cause widespread damage to the eastern coast of the United States - Hurricane Sandy is a grim reminder of the menace of extreme weather events.

With the lowest central pressure of the 2012 hurricane season, Sandy may have caused up to $20 billion in damages, making it one of the costliest superstorms in history.

Sandy interacted with a weather system moving towards it from the east, posing difficult challenges for forecasters and nearly unprecedented weather conditions for the region. A similar storm hit New England 20 years ago. But Sandy was worse, delivering hurricane-strength winds, drenching rains, and severe coastal flooding throughout the populous mid-Atlantic and northeast corridor.

Some people will, of course, try to link Sandy with climate change. A similar rush to judgment occurred in the wake of massive tornado outbreaks in the US in recent years, even though the scientific literature does not offer strong support for such a connection. So, from the perspective of climate change, it is best to take a measured view of Sandy, lest hasty reaction harm scientific credibility.

But that is little cause for comfort. According to the giant insurance company Munich Re, weather and climate disasters contributed to more than one-third of a trillion dollars in damage worldwide in 2011, and this year's total may rival that amount. There is growing evidence of links between climate change and sea-level rise, heat waves, droughts, and rainfall intensity, and, although scientific research on hurricanes and tornadoes is not as conclusive, that may be changing.

Indeed, recent reports by the United Nations' Intergovernmental Panel on Climate Change (IPCC) and other scientific literature suggest that the intensity of tropical cyclones (that is, hurricanes) will increase as a result of warmer waters. And our atmosphere and oceans are, indeed, warming, with substantial residual heat stored in the ocean, to be released at some future time. A few studies have even suggested that tropical cyclones may be "wetter". It is quite certain that sea levels have risen over the last century, and continue to rise, in response to changing climate. And storm surges now ride on these elevated sea levels, amplifying flooding losses where they strike.

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Sea surface temperatures along the US northeast coast are about 5 degrees Fahrenheit above average, which helped to intensify Sandy just prior to landfall. At this point, it is premature to link the storm's severity to warmer sea-surface temperatures, because regional variability is known to occur. But the link certainly is plausible.

Moreover, sea levels along the US northeast coast are rising up to four times faster than the global average, making the region more vulnerable to storm surges and flooding. And here the bottom line is that any coastal storm system will produce more flooding because of sea level rise.

It should also be noted that an atmospheric weather pattern known as a "block", a persistent area of high pressure that may have led to record melting in Greenland, was most likely the reason that Sandy moved inland rather than out to sea. It is too early to tell whether this blocking pattern is a manifestation of weather variability, a short-term climate variation, or the result of climate change.

Advances in numerical weather forecasting have extended our ability to "see" into the future. In September 1938, before all of these advances, a hurricane devastated much of New England. No warnings were issued prior to its arrival. Today, thanks to satellites, weather balloons, supercomputers, and skilled forecasters, we can anticipate hazardous weather up to a week in advance.

Similar advances in climate modelling are occurring, thanks to methodological improvements and better data.

At a minimum, we must ensure that world-class weather and climate-modelling centres have the necessary funding and manpower to implement the most advanced forecasting techniques.

The world will need more co-operation in the coming years, as climate change begins to interact with and exacerbate extreme weather events, in order to gain the lead-time needed to prepare for disasters. We will also need the collaboration among governments, the private sector, and academia that often leads to improvements in forecasting.

Scientific meetings are key forums for sharing research, vetting new methodologies, and forging new partnerships. Many occur on an international basis, and we need to encourage such discourse, even in tough times for government budgets. It is reasonable to ask how well we would be able to predict or assess a storm like Sandy without the knowledge and capacity gained through such international collaboration.

We do not know whether superstorms like Sandy are harbingers of a "new normal" in the uneasy and unpredictable relationship between climate change and extreme weather events. That does not mean that there is not or cannot be such a connection, but rather that the scientific research needed to prove (or disprove) it must still be conducted.

That is how good science works. Sandy has provided a powerful demonstration of the need to support it.

J Marshall Shepherd, director of the Atmospheric Sciences Programme at the University of Georgia, is President-Elect of the American Meteorological Society.

- © Fairfax NZ News

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