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 the work that establishes this in Nature (August 13, 2009).
Fewer Hurricanes Predicted for 2009
The National Oceanic and Atmospheric Administration (NOAA) has lowered its predictions for the 2009 hurricane season that began on May 15. It ends on November 30, with the peak activity period being August to October.
In an August 6, 2009 bulletin, NOAA’s hurricane prediction centre now says there is “a 70 percent chance of seven to 11 named storms, of which three to six could become hurricanes, including one to two major hurricanes (category 3, 4, or 5).”
That’s a drop from NOAA’s May 2009 forecast of 14 named storms. One year’s activity cannot be taken to indicate a trend, which is that there has been a recent increase in tropical cyclones.
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 13, 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.
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 31, 2009) 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.
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