Week of October 13th

Hurricanes and Climate Change- notes on one disputed point in an inconvenient truth

• new study in Nature Science journal says that hurricanes and typhoons are stronger and longer over the past 30 years- The duration and strength have increased by a factor of 50%
• Usually a 1 degree C increase in water temperature results in a 5% increased intensity of storms. We have had a .5 degree C increase and much greater effects than would be expected
• How hurricanes work- heat results in warmer water which results in more evaportation. More storms are picked up by low pressure systems and the spin of the earth causes storms to whirl around center of low pressure. All driven by warm air.
• Hurricanes form over water with a temperature above 26 degrees C as a rule
• Some argue hurricane intensity fluctuates on a decade to decade basis, based on factors like El Nino, other argue that worldwide these strong interdecadal swings cancel out and we see an upward trend of increasing hurricane intensity
• Others argue that currently the number of hurricanes is holding steady
• According to Nature article- a 1 degree C increase in sea temperature is currnelty resulting in a 31%increase in global frequency of category 4 and 5 hurricanes. Add to that fact that ocean temperatures could increase by 2 degrees C by 2100
• Some argue that climate models work well on the global level but can't be applied accurately to areas smaller than 200 square miles- which is larger than many storms
• Mr Knutson and friends at NASA's geophysical fluid dynamics lab in Princeton produced a year by year "hindcast" of hurricane numbers over the past 30 years. They predict an 18% decrease in annual hurricane count by late this century. They argue that what matters in hurricane formation is the difference in temperature between the sea and the top of the troposphere (the weather zone of the atmosphere) and global warming will warm the troposphere faster than it will warm the Atlantic. Others argue that there are flaws in the model used by Mr. Knutson in that it cant produce big storms and with an increase in large storms in the future, and the number of overall storms staying the same, of couse the number of small storms would decrease.
• Kerry Emanuel (from MIT) wrote an article in the March 2008 Bulletin of the American Meteorological Society claiming that the results of climate moels suggerst other factors are likely to contribute to the increase in the number of storms, refuting his previous claim that global warming is the main contributor to the increase in the number of storms. His team inserted seeds of tropical storms throughout climate models and observed which develop into tropical storms and hurricanes. They found that the over all number of hurricanes will decrease over the next 2 centuries but hurricanes in general will increase in intensity. There is some uncertainty in the study in that the climate models show that in some areas intensity will increase and it others it will actually decrease.
• Others claim that research in general about this issue is difficult because the hurricane record pre-1970 is entirely unreliable and climate models cannot detect individual tropical storms.
• Some records- based off the number of people dieing and money being lost due to hurricanes- are unreliable because the information is skewed due to more people living in hurricane zones
• Some argue the path of hurricanes will change due to global warming (think of jet streams and conveyer belt)
• Johan Nyberg of Geological Survey of Sweden used coral samples from the North East Carribean to build a record to wind sheer and sea surface temperature dating back to 1730. Wind sheer is the difference in speed and dirrection between low winds and higher winds and causes a decrease in rainfall which causes denser coral. An increase in wind sheer decreases the number of hurricanes because it breaks up the systems as they form and a decrease in hurricanes results in less rainfall which results in denser coral. Nyberg foiund that the frequency of major hurricanes decreased gradually since the 1760s and had an all time low between the 1970s and 1980s. He argues that we are just returning to the norm. Elsner counter argues that the north east Carribean might not have always been in the dirrect path of hurricanes
• The World Meteorological Organization (WMO) (a group of 125 experts) said that "given the consistancy between high resolution global models, regional hurricane models and maximum potential intensity theories it is likely that some increase in tropical cyclone intensity will occur if the climate continues to warm"
• Others focus on the why the North Atlantic (the focus of many of the studies are done because it is where US hurricanes gather strength) is an exception. They argue that most tropical climates have an average sea temperature of 26 degrees C all year round, while the temperature of the North Atlantic fluctuates below and above this temperature, making this temperature a switch for hurricanes. The North Atlantic is therefore more sensitive to sea surface temperatures
• A survey by Mr. Holland found that starting in 1905 for about 25 years there were about 6 tropical storms a year. Starting in 1931 there were about 9.4 storms a year and between 1995 and 2005 there have been about 14.8 storms a year. Between 1931 and 1994 there was no long term variation in the number of storms and then the number increased signficiantly in 1995. This corresponds with and increase in sea temperatures Holland argues. Others contend that there are cycles of 30 to 40 years of quiet followed by 30 to 40 years of business.
• Chris Landsea at NOAA's National Hurrican Center claims that the reason the number of hurricanes seems to be increasing is due to fact that storms previously not picked up by meteorologists are now better detected due to new technology. He claims there are many "missing storms" in old data.
• Brian Soden (from the University of Miami in Florida) used 18 climate models to study this issue. He claims that an increase in vertical wind sheer caused by climate change will counter balance the warming effect. He says that in the upper atmosphere westerly winds will increase "sheering" against easterly winds in the lower atmosphere, which is what he calls a change in the Walker circulation. He says this will occur in some areas more than others. He compares this change to the similar shifts in Walker circulation during El Nino years. Emanuel counter-argues that sensitivity to windsheer is probably overestimated stating that a 10% increase in water temperature results in a 65% increase in the intensity of storms while a 10% increase in wind sheer resuls in only a 12 % decrease in the intensity of storms.
• The media also influences the issue. For example the media always publicizes big hurricanes and big hurricane years but ignored that fact that 2007 was one of the calmed hurricane seasons in the North Atlantic in 30 years. Some argue that this is because a slow warming does not make for memorable images on tv and when judging risks, due to the avalability heuristic, we gauge a danger according to how many examples of ti are available in out minds. Therefore, some believe, that the manipulation by the media helps the fight to end global warming

Long story short, no one knows for sure whether the increase in hurricanes and tropical storms is caused by climate change. Both the inaccuracy of climate models and the lack of sufficient hurricane records result in the inability to know what is really going on, however, the general concensus among scientists is that whether or not the number of storms is increasing, their intensity definately is. Therefore, we can't wait for more data, we have to act now! As for the inconvenient truth, a very disputed issue is presented as fact by Al Gore, which in my eyes is an issue especially when so many people will believe what he says. He isn't talking to a scientifically knowledgable audience and should be careful not to manipulate their views. All in all, however, his view is supported by many scientists, even if it is just a theory. Right now theory is all we have and people wont act off just theory, but we have to act. So maybe, as far as the movement to end climate change is concerned, presenting theory as fact is a necessity. We can decide later whether the manipulation of the general public was worth it or neccessary, after we get global warming under control.

Articles used (not a real bibliography, just some imporant information in case we want to use the articals in the future):

"Wind Sheer may Cancel Climate's Effect on Hurricanes" from NewScientist.com by Phil McKenna published in April 2007.

"In 2008, a 100% Chance of Alarm" from the New York Times by John Tierney published in January 2008

"Tropical Storms Stepping up with Climate Change" from NewScientist.com by Jeff Hecht pubished in September 2007

"Global Warming link to Hurricanes Likely but Unproven" from NewScientist.com by Catherine Brahic published in December 2006

"Coral Reveals Increased Hurricanes May be Norm" from NewScientist.com by Catherine Brahic published in June 2007

"Climate Myths: Hurricane Katrina was Caused by Global Warming" from NewScientist.com by Emma Young published in May 2007

"Hurricane Expert Reconsiders Global Warming's Impact" from Chron.com by Eric Berger published in 2008

"Analysis: Will Warming Really Lead to Fewer Atlantic Hurricanes" from New Scientist Journal by Fred Pearce published in May 2008

"Is Global Warming Worsening Hurricanes?" from Time.com by Bryan Walsh published in September 2008

"Is Global Warming Making Hurricanes Worse" from NationalGeographic.com by John Roach published in August 2005