Claim:

STRONGER HURRICANES

Based on data from an August 2005 paper, "Increasing destructiveness of tropical cyclones over the past 30 years," published in Nature by MIT's Dr. Kerry Emanuel. (Courtesy of Clear the Air, http://www.cleartheair.org)

"Now I’m going to show you, recently released, the actual ocean temperature. Of course when the oceans get warmer that causes stronger storms. We have seen in the last couple of years, a lot of big hurricanes. Hurricanes Jean, Francis and Ivan were among them. In the same year we had that string of big hurricanes; we also set an all time record for tornadoes in the United States. Japan again didn’t get as much attention in our news media, but they set an all time record for typhoons. The previous record was seven. Here are all ten of the ones they had in 2004. The science textbooks that have to be re-written because they say it is impossible to have a hurricane in the South Atlantic. It was the same year that the first one that ever hit Brazil. The summer of 2005 is one for the books. The first one was Emily that socked into Yucatan... And then of course came Katrina. It is worth remembering that when it hit Florida it was a Category 1, but it killed a lot of people and caused billions of dollars worth of damage. And then, what happened? Before it hit New Orleans, it went over warmer water. As the water temperature increases, the wind velocity increases and the moisture content increases... the consequences were so horrendous; there are no words to describe it."

- Al Gore, "An Inconvenient Truth"(1)

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Implications:

Global warming, causing an increase in sea surface temperatures, would also result in stronger and more intense tropical cyclones. These trends would lead to devastating effects on the "ever-growing concentration of population and wealth in the vulnerable coastal regions" (10). Ultimately, without government support and involvement, there would high human and economic losses from future hurricane disasters.

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General Information:

Hurricanes, typhoons, cyclones:

1. What are the major differences?
According to the Atlantic Ocreanographic and Meteorological Laboratory, “hurricane" and “typhoon” are all region-specific names for the same thing: strong “tropical cyclone”. (5)

2. What is a tropical cyclone, then?

(Courtesy of Union of Concerned Scientists, http://www.ucsusa.org/global_warming/science/hurricanes-and-climate-change.html)

Essentially, tropical cyclones form when two conditions are met, the creation of a low pressure center and existence of thunderstorms. Low pressure centers form when ocean temperatures increase, which leads the air pressure over the ocean to fall. It is this decrease in pressure that serves as the foundation of the low pressure center characteristic of tropical cyclones. In addition, thunderstorms are necessary for the birth of a tropical cyclone because thunderstorms provide strong winds and heavy rainfall.  Tropical cyclones gains momentum as warm, moist air rises, cools, and condenses to rain, releasing heat in the process. It is this cycle of evaporation and condensation that provide “energy” to strengthen the storm. (7) According to the ational Oceanic and Atmospheric Administration, "a tropical cyclone can be visualized as a giant vertical heat engine supported by mechanics driven by physical forces such as the rotation and gravity of the Earth" (5).

3. What are the intensity classifications for tropical cyclones?

Tropical depressions: Tropical cyclones that have maximum surface winds of less than 17 m/s (or 39 mph).

Tropical storms: Tropical cyclones that intensify and reach maximum surface winds of at least 17 m/3. Tropical cyclones are assigned names upon reaching this level.

However, if the tropical cyclone intensifies even more, and reaches maximum surface winds of 33m/s (or 74mph), then they are given region specific titles:

• “Hurricane”: Regionally specific to the North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline, or the South Pacific Ocean east 160E
• “Typhoon”: Northwest Pacific Ocean west of the dateline
• “Severe tropical cyclone”: Southwest Pacific Ocean west of 160E or Southeast Indian Ocean east of 90E
• “Severe cyclonic storm”: North Indian Ocean
• Tropical cyclone”: Southwest Indian Ocean (5)

4. What are the seven basins and what is their importance?

There are seven tropical cyclone "basins" where storms occur on a regular basis:
1. Atlantic basin, including the North Atlantic Ocean, the Gulf of Mexico, and the Caribbean Sea
2. Northeast Pacific basin.from Mexico to about the dateline
3. Northwest Pacific basin.from the dateline to Asia including the South China Sea
4. North Indian basin, including the Bay of Bengal and the Arabian Sea
5. Southwest Indian basin.from Africa to about 100E
6. Southeast Indian/Australian basin (100E to 142E)
7. Australian/Southwest Pacific basin (142E to about 120W)

Image of the Seven Bains (Curtesy of NOAA, http://www.aoml.noaa.gov/phod/cyclone/data/seven.html)

According to NOAA's National Hurricane Center, about 69% of tropical cyclones occur in the Northern Hemisphere, and only 31% occurs througout the Southern Hemisphere. In addition, about 12% of tropical cyclones occur in the Atlantic Ocean, 57% occur in the Pacific Ocean, and the other 31% occur in the Indian Ocean. (12)

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Support for Claim:

1. IPCC Summary notes: “The surfaces of most tropical oceans have warmed by 0.25-0.5 degree Celsius during the past several decades. The intergovernmental Panel on Climate change considers that the likely cause of the rise in global mean surface temperature in the past 50 years is the increase in greenhouse gas concentrations… Some recent scientific articles have reported a large increase in tropical cyclone energy, numbers, and wind speeds in some regions during the last few decades in association with warmer sea surface temperatures. Other studies report that changes in observational techniques and instrumentation are responsible for these increases.” (6)

2. The consensus developed by the "global community of tropical cyclone researchers and forecasters as represented at the 6th International Workshop on Tropical Cyclones of the World Meteorological Organization, which took place during November 2006, stated among their list...agreement point six, "It is likely that ome increase in tropical cyclone peak wind speed and rainfall will occur if the climate continues to warm. Model studies and theory project a 3-5% increase in wind-speed per degree Celsius increase of tropical sea surface temperatures" (6).

Getting warmer. Annual mean SST anomalies relative to 1961 to 1990 (23) for 1870 to 2004, averaged over the tropical Atlantic (10°N to 20°N) (top) and the North Atlantic (30°N to 65°N) (bottom). Heavy lines are 10-year running means. (Curtesy of Science Magazine, http://www.sciencemag.org/cgi/content/full/308/5729/1753/F1) (11)

3. In a report on global warming and its effect on hurricane activity, the National Oceanic and Atmospheric Administration mention a hurricane simulation study carried out by Thomas R. Knutson and Robert E. Tuleya at NOAA's Geophysical Fluid Dynamics Laboratory. In this study, hurricanes were simulated based in projected climate changes that would result from an increasing build up of Co2. The simulation was based on projected CO2 build up for 80 years, at 1% per year (compounded). From this study, the scientists concluded that "The strongest hurricanes in the present climate may be upstaged by even more intense hurricanes over the next century as the earth's climate is warmed by ncreasing levels of greenhouse gases in the atmosphere" (GDFL, 2007). (6)

Comparison of simulated hurricane intensities for present-day (thin line) and future (thick line) climate conditions assuming an 80-year build-up of atmospheric CO2 at 1%/yr compounded. The results are aggregated from sets of experiments using nine different global climate model projections and four different versions of a high-resolution hurricane prediction model (Curtesy of Geophysical fluid Dynamics Laboratory, http://www.gfdl.noaa.gov)

4. There is also support for Gore's claim through dispelling existing counterclaims. According to a science article by M.E Mann and K.A Emanuel, hurricane trends in the Atlantic cannot be attributed to natural variability, known as the Atlantic Multidecadal Oscillation (AMO). In recent studies, AMO has been described as attributing increased hurricane activity "to a natural climate cycle" (Mann, 2006, 233) However, Mann and Emanuel point out the many inconsistencies with this claim. "Recent analyses...attribute the AMO as having a significantly greater influence on tropical North Atlantic SST" (Mann, 2006, 238). Therefore, how accurate is the AMO as an explanation for the variability in hurricane activity? In the end, Mann and Emanuel still conclude that "there is a strong historical relationship betwen trpical Atlantic SST and tropical cyclone activity extending back through the late 19th century. There is no apparent role of the AMO. The underlying factors appear to be the influence of (primarily anthropogenic) forced large-scale warming...(Mann, 2006, 241) (9)

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Counterclaim:

The E-Team

The National Center for Policy Analysis’ E-Team, is one of the largest collections of energy and environmental policy experts and scientists who believe in sound science and that economic prosperity and protecting the environment can go hand and hand. The Team seeks to correct misinformation and promote sensible solutions to energy and environment problems.

Support for Counter Claim

1. Not enough data to base claims
An argument brought up by E-Team member, H. Sterling Burnett, in his article “The Political Climate”, states that “hurricane physics, historical data and ongoing hurricane research indicate that there is scant, if any, evidence linking human caused global warming to the frequency or ferocity of hurricanes.” (2)

Support for this claim: There are many scientists who point to a lack of data as a factor that has been limiting research in this frield. For instance, Webster et al. in their study of changes in tropical cyclone characteristics in a warming environment, noted that their research was limited to data collected from the satellite era because “of the known biases before this period”. They also stress that an analysis based on longer periods of oscillation and trends has still not been attempted (13)

2. Hurricanes occur due to natural variability in climate
In the article, Burnett points out how at the 27th annual National Hurricane conference of Colorado, Dr. William Gray, “explained that nature s responsible for hurricane cycles, not humans”. Burnett also argues that 2004’s hurricane session is a part of a natural cycle that “scientists have been monitoring for more than 100 years”. Furthermore, he states that according to the history of hurricanes, the US’s current hurricane trends are similar to those from the 1930’s to the 1950’s, in which out of the 23 hurricanes that “hit the US mainland in the 1940s, 8 were category 3 or stronger storms", implying that there once was a trend of historically strong cyclone activity (2).

Support for Claim: It is true that hurricane cycles oscillate- they are after influenced by other factors that vary over time as well. Even looking at the carbon dioxide levels from 500 million years ago, we can note great variations and oscillations.

The following figures shows estimates of the changes in carbon dioxide concentrations during the Phanerozoic millions of years ago. The three model estimates are based on geochemical modeling: GEOCRAB III (Berner and Kothavala 2001), COPSE (Bergmann et al. 2004) and Rothman (2001). The three models are compared to the carbon dioxide measurement database of Royer et al. (2004) and a 30 Myr filtered average of those data. (Curtesy of Wikipedia, http://www.globalwarmingart.com)

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Analysis of Arguments:

Both sides point to very important arguments, and ultimately both are neither completely correct or completely incorrect. As the first of the consensus statements put out by the World Meterological Organizations states, "Though there is evidence both for and against the existence of a detectable anthropogenis signal in the topical cyclone climate record to date, no firm conclusion can be made on his point" (GFDL, 2006) (6). However, there seems to be a general agreement in the scientific that coastal regions will be extremely vulnerable. Even the E-Team has recognized that coastal areas are much more populated than they used to be. There are scientists who feel that the debate is focusing on the wrong issue- according to Kevin Ternberth, "The key scientific question is not weather there is a trend in hurricane numbers and tracks, but rather how hurricanes are changing" (Ternberth, 2005, 1753) (11). Therefore, "it is vital to also gain a physical understanding of the changes in hurricane activities and their origins" (Ternberth, 2005, 1754).(11)

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Possible Outcomes:

If the general perception that "warming may lead to an upward trend in tropical cyclone destructive potential, and - taking into account an increasing coastal population- a substantial increase in hurricane-related losses in the 20th century" (Emanuel, 2005, 6868) is indeed true, then drastic measures must be taken to strengthen vulnerable coastal areas (4). According to Emanuel, "Private property insurance is heavily regulatrd by each state, and political pressure keeps rates low in hig-risk regions like tropical coastlines, thus encouraging people to build flimsy structures there... Federal flood insurance pays for storm surge damage, and like private insurance, its rates do not reflect the true risk (Emmanuel, 2006) (3).

References

1. Guggenheim, D. (director). An Inconvenient Truth [Motion Picture]. Hollywood, CA: Paramount.  

2. Burnett, H. S. (2005, November). The Political Climate. E-Team. Retrieved November 28, 2007, from http://eteam.ncpa.org/commentaries/the-political-climate   

3. Emanuel, K. (2006, January). Anthropogenic Effects on Tropical Cyclone Activity. MIT. Retrieved on November 28, 2007, from http://wind.mit.edu/~emanuel/anthro2.htm  

4. Emanuel, K. (2005). Increasing Destructiveness of Tropical Cyclones Over the Past 30 Years. Nature, 436.4:  686-688.    

5. National Oceanic and Atmospheric Administration: Hurricane Research Division (2007). FAQ: Hurricanes, Typhoons, and Tropical Cyclones. Retrieved on November 28, 2007, from http://www.aoml.noaa.gov/hrd/tcfaq/A1.html  

6. Geophysical fluid Dynamics Laboratory: National Oceanic and Atmospheric Administration (2007, November).Global Warming and Hurricanes. Retrieved on November 28, 2007, from http://www.gfdl.noaa.gov/~tk/glob_warm_hurr.html 

7. Union of Concerned Scientists (2007). Hurricanes and Climate Change." Retrieved on November 28, 2007, from http://www.ucsusa.org/global_warming/science/hurricanes-and-climate-change.html 

8. Landsea, C.W., Harper, B., Hoarau, K., & Knaff, J (2006). Can We Detect Trends in Extreme Tropical Cyclones?” Perspectives 313, 425-453.  

9. Mann, M. E., & Emanuel, K.A. (2006). Atlantic Hurricane Trends Linked to Climate Change. Eos 87, 233+.    

10. Massachusetts Institute of Technology (2006). Statement on the US Hurricane Problem." MIT. Retrieved on November 28, 2007, from http://wind.mit.edu/~emanuel/Hurricane_threat.htm 

11. Trenbarth, K (2005). Uncertainty in Hurricanes and Global Warming. Science 208, 1753-1754. 

12. National Oceanic and Atmospheric Administration (2007, December). Tropical Cyclone Heat Potential. Retrieved on December 2, 2007, from http://wind.mit.edu/~emanuel/anthro2.htm

13.  Webster, P. J., G J. Holland, J. A. Curry, and H. R. Chang. "Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment." Science 309: 1844-1846.

V1003 Science and Society. Professor deMenocal Fall 2007. Kimberly Wu, Ryan Delgado, Isaiah Powell, and Cindy Choung