Hurricanes Becoming more Frequent

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25 November 2010

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Hurricanes Becoming more Frequent

During the last decade there has been an average of 17 hurricanes and tropical storms in the Atlantic each year; that’s double the number of earlier in the 20th century

Scientists have determined that the annual number of Atlantic hurricanes is higher now than at any time in the last 1,000 years. Dr. Michael Mann from Penn State University and his team have published their work in Nature (August 2009).

Sediment Gives Clues to Past Storms

The scientists from Penn State University have been studying sediments in hurricane-prone regions. When these massive storms hit land they pick up sand and earth and carry it inland before dumping it.

BBC News reporting on the study (August 2009) writes that, “In places where there is a lagoon behind the shoreline, this leads to ‘overwash’ - material from the shore being deposited in the lagoon, where it forms a layer in the sediment.”

Researchers studying these sediments were able to make their determination about the frequency of hurricanes in past centuries.

Climate Change and Hurricanes

Most climatologists believe the frequency of storm activity is connected to global warming, although there is a vigorous debate on this issue.

The Penn State research shows that the last time hurricane frequency was similar to today’s was about 1,000 years ago during the Mediaeval Warm Period.

The BBC quotes Julian Heming, a tropical storm specialist from the U.K.’s Meteorological Office as saying this latest study is “worth feeding into the debate about whether what we’re seeing now is exceptional or something related to multi-decadal or even multi-centennial variability; and it does tell us that the levels we’re seeing at the moment are within the bounds of uncertainty.”

The Penn State study adds another piece to the global warming puzzle.

This is what Hurricane Mitch did to Tegucigalpa, capital of Honduras in November 1998. Mitch was one of the deadliest hurricanes in the region killing nearly 11,000 people. The Category 5 storm had sustained winds of 285 km/h.

Tropical Atlantic Water Warming

Hurricanes draw their energy from the heat in tropical waters and ocean temperatures have climbed in the last couple of decades.

ScienceDaily.com reported (January 2008) that, “The link between changes in the temperature of the sea’s surface and increases in North Atlantic hurricane activity has been quantified for the first time.”

The research was conducted by University College London and showed “that a 0.5°C increase in sea surface temperature can be associated with an approximately 40 percent increase in hurricane activity.”

According to Princeton University research published in 2006, the surface temperature of the tropical Atlantic increased in the “range from 0.32°C to 0.67°C over the 20th century.” Computer climate models predict the water is going to continue to get warmer throughout this century.

Image credits

National Oceanic and Atmospheric Administration

Sources

“Atlantic Hurricanes and Climate over the Past 1,500 years.” Michael E. Mann et al, Nature, August 13, 2009.

“Many Hurricanes in Modern Times.” Richard Black, BBC News, August 13, 2009.

“Hurricane Season in 2010 Making History.” Greg Postel, Washington Post, 18 November 2010.

“Surprisingly, Hurricanes Avoid U.S. Landfall in 2010.” Andrea Leontiou,Our Amazing Planet, October 26, 2010.

“Increased Hurricane Activity Linked to Sea Surface Warming.” Science Daily, January 31, 2008.

2010 A BUSY

HURRICANE SEASON

“Long-range forecasts made last spring for the 2010 Atlantic hurricane season almost unanimously predicted lots of storms. Though they generally under-forecast how many we would actually observe, they were right it would be an active season.”

That’s Greg Postel, writing in the Washington Post (November 18, 2010), and he points out there were 19 named storms in 2010, set against an average of 10. Of these 12 were hurricanes; double the long-term average, and five were major hurricanes (the average is two).

If it didn’t seem like a very active season that’s because the storms largely left the United States untouched. At Our Amazing Planet, Andrea Leontiou (October 26, 2010) says “Since 1900, there is no precedent of an Atlantic hurricane season with 10 or more hurricanes where none has struck the United States...but that’s exactly what happened this year.”

While the continental United States dodged bad weather in 2010, University of Hawaii in Honolulu researcher Tim Li forecasts his home state may be in for some foul conditions. According to New Scientist (October 2010), When Li “factored in the impact of global warming, he found that by the end of this century, the frequency of tropical cyclones will have fallen by 31 percent over south-east Asia and grown by 65 percent over the north central Pacific.”

SAFFIR-SIMPSON

HURRICANE SCALE

in km/h

Tropical depression -

0 - 62

Tropical storm - 63 - 118

Category 1 - 119 - 153

Category 2 - 154 - 177

Category 3 - 178 - 209

Category 4 - 210 - 249

Category 5 - 250+

Following the devastating season of 2005 - Hurricane Katrina, Rita, and others - a suggestion was made to add a Category 6 for storms with winds in excess of 287 km/h

Category 1 winds can topple mobile homes that are not anchored and bring down small trees.

Category 5 storms can bring down entire homes and industrial buildings.

One of the biggest concerns with hurricanes is that winds cause a buildup of ocean water, called storm surges, that can be more than 10 metres high and travel inland many kilometres in low-lying areas.

Canadian Hurricane Centre