QUOTE(New Scientist)
A massive global increase in the number of strong hurricanes over the past 35 years is being blamed on global warming, by the most detailed study yet. The US scientists warn that Katrina-strength hurricanes could become the norm.
Worldwide since the 1970s, there has been a near-doubling in the number of Category 4 and 5 storms – the strength that saw Hurricane Katrina do such damage to the US Gulf coastline late in August 2005.
Peter Webster of the Georgia Institute of Technology, Atlanta, says the trend is global, has lasted over several decades and is connected to a steady worldwide increase in tropical sea temperatures. Because of all these factors, it is unlikely to be due to any known natural fluctuations in climate such as El Niño, the North Atlantic Oscillation or the Pacific Decadal Oscillation.
“We can say with confidence that the trends in sea surface temperatures and hurricane intensity are connected to climate change,” says Webster’s co-author Judy Curry, also of the Georgia Institute of Technology. The team looked at the incidence of intense tropical storms and the study results are the strongest affirmation yet that Katrina-level hurricanes are becoming more frequent in a warmer world.
Unnatural trend
The study finds there has been no general increase in the total number of hurricanes, which are called cyclones when they appear outside the Atlantic. Nor is there any evidence of the formation of the oft-predicted “super-hurricanes”. The worst hurricane in any year is usually no stronger than in previous years during the study period.
But the proportion of hurricanes reaching categories 4 or 5 – with wind speeds above 56 metres per second – has risen from 20% in the 1970s to 35% in the past decade.
“This trend has lasted for more than 30 years now. So the chances of it being natural are fairly remote,” says Greg Holland of the National Center for Atmospheric Research (NCAR) at Boulder, Colorado
Moreover, says Webster, natural fluctuations tend to be localised. “When the east Pacific warms, the west Pacific cools, for instance. But sea surface temperatures are rising throughout the tropics today.” The surface waters in the tropical oceans are now around 0.5°C warmer during hurricane seasons than 35 years ago.
Satellite era
Hurricanes form when ocean temperatures rise above 26°C. “The fuel for hurricanes is water vapour evaporating from the ocean surface. It condenses in the air and releases heat, which drives the hurricane’s intensity,” says Webster.
“The tendency to Katrina-like hurricanes is increasing,” Holland says. Without the warmer sea-surface temperatures, “Katrina might only have been a category 2 or 3”.
All the data for sea surface temperatures and hurricane numbers and intensities come from satellite data. “We deliberately limited this study to the satellite era because of the known biases [in the data] before this period,” says Webster.
This is the third report in recent months highlighting the growing risk to life and property round the world from hurricanes and tornadoes. In June, NCAR’s Kevin Trenberth reported a rising intensity of hurricanes in the North Atlantic.
And in August, Kerry Emanuel of MIT found a 50% increase in the destructive power of tropical storms in the past half century.
Journal reference: Science (vol 309, p 1844)
Heh, NS beats PS anyday. bluetongue.gif Oh, and for Alpha:
QUOTE(New Scientist)
AS NAILS in the coffin go, they don't get much bigger: three independent studies have shown that climate sceptics who claim that Earth is not warming have been using faulty data to make their point.
The debate on climate change has often centred on the temperature of the lower troposphere. Common sense and computer models suggest that as the Earth's surface warms, so should this layer of the atmosphere. But measurements from satellites and balloons did not always support this.
In 1992, John Christy of the University of Alabama in Huntsville analysed the satellite measurements and concluded that the lower troposphere had cooled over the decades, relative to Earth's surface over the tropics. For those arguing against global warming, this analysis was pure gold. "The data from the satellites have taken on almost iconic status," says Ben Santer of the Lawrence Livermore National Laboratory in California.
But the findings remained puzzling. "It is very difficult to understand physically how the lower troposphere could be cooling while the Earth's surface and the middle and upper troposphere were warming, as this study found," Santer says.
Now Carl Mears and Frank Wentz of Remote Sensing Systems in Santa Rosa, California, have an answer. They reanalysed Christy's data and corrected for errors caused by satellite drift. "The satellite is supposed to go over the equator and take measurements at the same time every day," says Mears. Initially this was at around 2 pm local time, but after a few years it was crossing the equator at 5 pm, he says. "Common sense tells you that it's cooler at 5 pm than at 2 pm, and that was biasing the results." Once they factored this in, the data showed that the troposphere is warming (Science, DOI: 10.1126/science.1114772).
Mears and Wentz have strong support from Santer and his colleagues, who used 19 climate models to simulate the changes that would have occurred during the course of the 20th century. "Despite the fact that these models are all different in their physics, they all yield similar results in the tropics," he says. They all predict that warming at the Earth's surface should be amplified in the troposphere. "This makes sense physically," Santer says (Science, DOI: 10.1126/science.1114867).
Mears agrees. "The only thing left for sceptics to point at would be the weather balloon data that also showed discrepancy with the models." And now Steven Sherwood of Yale University in New Haven, Connecticut, and his colleagues have shown that the balloon measurements are unreliable too.
The problem has to do with protecting temperature sensors from direct sunlight. "It is just a little thing dangling from the balloon and there's no way to shield it consistently," Sherwood says. Over the years, researchers found new ways to shield the instruments from the sun, but rarely bothered to make a note of this shielding or calculate its effect on the raw data. Improved shielding led to a drop in the temperatures recorded by the sensors, and this can explain the trend of declining temperature in the troposphere as recorded by weather balloons, Sherwood says (Science, DOI: 10.1126/science.1115640).
Christy welcomes Mears and Wentz's analysis of the flaws in the satellite data he used. "Their suggestions helped me fix my error pretty quickly," he says. His reanalysis now shows the Earth is warming by about 1.23 °C per century. Mears and Wentz calculate the trend to be about 1.9 °C per century.
The world is not warming as fast as the 1.5 °C to 6 °C per century that models suggest, Christy says. "We all agree that warming is related to human effects, but it's not as dramatic as models say."
Sherwood agrees that the debate will linger. "I don't think we have resolved the controversy over global warming," he says. "But there is no longer any data contradicting the predictions of global warming models."
Some other non-quote points:
1. A small island below NZ is inhabited by an endemic species of lizard. A baby lizard's gender is decided by the incubation tempreture. This lizard is now dying out because of one reason: Global Warming. Because of the raised tempreture females are becoming scarce, and therefore the species is dying out.
2. You come to Australia and say there is no Global Warming, with dam levels <30% capacity and ranches going broke and whole scores of cattle dying.
Alpha is right though, we really shouldn't worry too much. I heard that the tempreture rose 10 degrees at the start of the Age of the dinosaurs, almsot twice the 6 degrees expected for Global Warming (only thing is, over 90% of all species died, but who cares as long as we can get to work on time and have fewer taxes?).
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