Question 9

Are hurricanes, other tropical cyclones and associated extreme weather events increasing in severity and frequency?

1st expert response by Professor William Gray

William M. “Bill” Gray (born 1929) is a pioneer in the science of forecasting hurricanes.[1] In 1952 he received a B.S. degree in geography from George Washington University, and in 1959 a M.S. in meteorology from the University of Chicago, where he went on to earn a Ph.D. in geophysical sciences in 1964. Dr Gray is Emeritus Professor of Atmospheric Science at Colorado State University (CSU), and head of the Tropical Meteorology Project at CSU’s Department of Atmospheric Sciences. He served as a weather forecaster for the United States Air Force, and as a research assistant in the University of Chicago Department of Meteorology. He joined Colorado State University in 1961. He has been advisor of over 70 Ph.D. and M.S. students. Dr Gray is noted for his forecasts of Atlantic hurricane season activity. He pioneered the concept of “seasonal” hurricane forecasting—predicting months in advance the severity of the coming hurricane season. Dr Gray and his team (including Christopher W. Landsea, Paul W. Mielke Jr., and Kenneth J. Berry, among others) has been issuing seasonal hurricane forecasts since 1984.

Has Global Warming Been Responsible for any Changes in Global Tropical Cyclone Frequency and Intensity? (Answer, NO)

Recent arguments concerning global warming’s influence on causing tropical cyclones (hurricanes-typhoons) to become more frequent and more intense has been given much coverage in the media and by some published papers which claim a valid linkage.  But observational data shows no such linkage.  Despite the global warming of the sea surface that has taken place between the mid 1970s to the late 1990s and the general global warming of the last century, the global numbers of tropical cyclones and hurricanes and their intensity have not shown any significant trends except for the Atlantic where multi-decadal circulation variations in the ocean drive large multi-decadal variations in major hurricane (Cat 3-4-5) numbers.

Net global Accumulated Cyclone Energy (ACE) of tropical cyclones (as measured by the integrated sum of each cyclone’s maximum wind speed squared (Vmax2) has shown a distinct decrease since the early 1990s and no trend since 1979 (Fig.1).  This lack of upward trend has occurred despite the continuous rise in atmospheric CO2 amounts.  Klotzbach (2006) also investigated global tropical cyclone activity in all six of the world’s tropical cyclone basins and did not find an upward trend in tropical cyclone frequency and intensity between 1986 and 2005 despite an upward trend in global tropical sea surface temperatures.


Figure 1:  Monthly sum of the globe’s tropical cyclone-generated Accumulated Cyclone Energy (ACE) (Vmax2) from January 1979 through November 2012

Theoretical considerations do not support a direct association between sea surface temperatures and hurricane intensity.  In a global warming or in a global cooling world, the atmosphere’s upper air temperatures will warm or cool in unison with the sea surface temperatures.  Vertical lapse rates will not be significantly altered.  We have no plausible physical reasons for believing that hurricane frequency or intensity will significantly change if global ocean temperatures were to continue to rise.  It is possible that rising future atmospheric CO2 levels may cause a small effect on global tropical cyclone activity.  But any such potential influence would be too small to ever be detectable, and at this point, we have no idea what the sign (plus or minus) of this influence would be.

Atlantic Ocean Considerations. The Atlantic has seen a very large increase in major hurricanes during the 15-year period of 1995-2009 (average 3.7 per year) in comparison to the prior 25-year period of 1970-1994 (average 1.5 per year).  This large increase in Atlantic major hurricanes is a result of the multi-decadal increase in the Atlantic Ocean thermohaline circulation (THC).  The THC is not related to global mean sea surface temperatures or to global CO2 increases.   Changes in ocean salinity are believed to be the driving mechanism.  The THC is the Atlantic component of the global ocean Meridional Overturning Circulation (MOC).

For instance, in the quarter-century period from 1945-1969 when the globe was undergoing a weak cooling trend, the Atlantic Ocean THC was strong, and the Atlantic experienced 80 major (Cat 3-4-5) hurricanes and 201 major hurricane days.  By contrast, in a similar 25-year period from 1970-1994 when the globe was undergoing a general warming trend and the Atlantic THC was weak, there were only 38 major hurricanes (48% as many) and 63 major hurricane days (31% as many) (Figure 2).  Long period normalized damage estimates indicate that landfalling major hurricanes, although accounting for only 20-25 percent of all hurricanes and tropical storms account for about 80-85 percent of all cyclone spawned destruction.


Figure 2:  Tracks of major (Category 3-4-5) hurricanes (Vmax > 50 ms-1) during the 25-year period of 1945-1969 when the globe was undergoing a weak cooling versus the 25-year period of 1970-1994 when the globe was undergoing a modest warming.  CO2 amounts in the later period were approximately 18 percent higher than in the earlier period.  Major Atlantic hurricane activity was only about one-third as frequent during the latter period despite warmer global temperatures and higher CO2 amounts.

The most reliable long-period hurricane records we have are the measurements of US landfalling tropical cyclones since 1900 (Table 1).  Although global mean ocean and Atlantic sea surface temperatures have increased by about 0.4oC between these two 55-year periods (1900-1954 compared with 1955-2009), the frequency of US landfall numbers actually shows a slight downward trend for the later period.  This downward trend is particularly noticeable for the US East Coast and Florida Peninsula where the difference in landfall of major (Category 3-4-5) hurricanes between the 44-year period of 1922-1965 (24 landfall events) and the 44-year period of 1966-2009 (7 landfall events) was especially large.  For the entire United States coastline, 38 major hurricanes made landfall during the earlier 44-year period (1922-1965) compared with only 26 for the latter 44-year period (1966-2009).  This occurred despite the fact that CO2 averaged approximately 365 parts per million (ppm) during the latter period compared with 310 ppm during the earlier period.  I and most of my colleagues who study hurricanes and typhoons believe that observational evidence does not support a linkage between tropical cyclone frequency or intensity and rising levels of atmospheric CO2 or global sea surface temperature changes.

Table 1:  U.S. landfalling tropical cyclones by intensity during two 55-year periods.

YEARS Named Storms Hurricanes Intense Hurricanes (Cat 3-4-5) Global Temperature Increase
1900-1954 (55 years) 208 113 44 +0.4oC
1955-2009 (55 years) 184 90 36

Klotzbach, P. J., 2006:  Trends in global tropical cyclone activity over the past twenty years (1986-2005).  Geophys. Res. Lett., 33, L10805, doi:10.1029/2006GL025881.
Klotzbach, P. J. and W. M. Gray, 2009:  Summary of the 2009 Atlantic Tropical Cyclone Activity and Verification of Authors’ Seasonal and 15-Day Forecasts. 49 pp. (
Maue, R. N., 2009:  Northern Hemisphere tropical cyclone activity.  Geophys. Res. Lett., 36, L05805, doi:10.1029/2008GL035946.

2nd expert response by Dr Madhav Khandekar

Dr Madhav Khandekar is a retired Meteorologist, formerly with Environment Canada (over 50 years in weather and climate science)

Historical incidence of tropical cyclones

This compilation of the incidence of hurricanes and tropical cyclones (TC) demonstrates that there has been no increase in the frequency or intensity in recent years. (Dates When records were set for various  Hurricane  parameters, based upon observed data and compiled from various web sites of agencies listed below*).

1). Most intense TC defined by central pressure. Typhoon Tip on 12 October 1979 in North West Pacific with a value of 870 hectopascals. Note that the lower the central pressure, the greater is the intensity.  By comparison, Hurricane Katrina of August 2005 is ranked number 54.  It does not solely can claim even this low rank, as it shares this spot with another TC. This means that there were at least 53 other TC that were stronger than Katrina.

2).Maximum sustained wind speed 85 meters per second, all the following TC can claim this record: Typhoon Tip on 12 October 1979. Typhoon Keith in 1997, Typhoon Vera in 1959, Typhoon Sara of 15th September 1959, Hurricane Camille in 1969 and Hurricane Allen in 1980.

3). Largest TC in size. Typhoon Tip on 12th October 1979 had a radius of 1,100 KM.

4). Smallest TC in Size. Hurricane Tracy on 24 December 1974 in Australia had a radius of 50 KM.

5). Which TC lasted the longest in the Pacific basin? Typhoon John lasted 31 days during August-September 1994.

6). Which TC lasted the longest in the Atlantic basin? Hurricane Ginger in 1971 lasted 27.25 days.  Some web sites give 30 days. Hurricane Inga in 1969 lasted 24.75 days.

7) Which TC lasted the longest in the south Indian Ocean? TC Elinor in 1983 lasted 20 days.

8). Most rapid intensification. Super Typhoon Irma on 15 May 1966 in the North West Pacific intensified by 51 hpa in 8 hours. and by 97 hpa in 24 hours.  Typhoon Forrest in North West pacific in September 1983 deepened from 976 to 876 hpa in just less than 24 hours.

9). Highest Storm surge. Bakergunj cyclone, Bangladesh , 1876, 13.6 m. Some web sites listed a value as high as 15 m for the Mahina cyclone of 5 March 1899 in Bathurst Bay , Australia . They also suggested that part of this might be wave set up. The Bhola cyclone of November 1970 in Bangladesh generated a peak surge of about 13 m. By comparison, the peak surge from Hurricane Katrina in 2005 was 8.5 m.

10). Greatest amount rainfall in 12 hours. At La Reunion in south west Indian Ocean from cyclone Denise  during 7 to 8 January 1966 with a total of 114.4 cm. By comparison, the amount of rain that fell in Philippines from a tropical storm on 26 Sept 2009 was 42.5 Cm.

11). Greatest amount of rainfall in 24 hours. Same place and same cyclone and same dates with a total of 182.5 cm

12). Greatest amount of rainfall in 48 hours.  Un-named TC at the same location during 8 to 10 April 1958 with a total of 246.7 cm.

13). Greatest amount of rainfall in 72 hours.  From TC Gamede at the same location during 1 to 3 March 2007, with a total of 392.9 cm. Another web site lists a different value of 324 cm from TC Hyacinthe during January 1980.

14). Greatest amount of rainfall during a 10 day period. From TC Hyacinthe at the same place during 18-27 January 1980.

15). Which TC travelled the farthest in the Atlantic . In 1966 Hurricane Faith travelled 12,500 Km.

16). Which TC travelled the farthest in east Pacific. Typhoon John in 1994 travelled 13,000 Km.

17). Which TC travelled the farthest in west pacific. Typhoon Ophelia in 1960 travelled 13,500 Km.

18). Which TC has been at category 5 for the longest time in the west Pacific. Nancy, 1961, (5.5 days), Karen, 1962, (4.25 days), Sally, 1954, (4 days), Dinah, 1959, (3.75 days), Nina, 1953, (3.5 days).

19). Which TC has been at category 5 for the longest time in east Pacific. Typhoon Paka in 1997 was for 2.5 days.

20). Which TC was at category 5 for the longest time in the north Atlantic. Hurricane Allen in 1980 was for 3 days. Hurricane Dog in 1950 was for 2.5 days.

21). Maximum number of deaths from a TC storm surge. About 300,000 in Bangladesh in November 1970.

22). Maximum damages (in 2005 US dollars) anywhere on the globe from a TC.
1926 Great Miami Hurricane. 157 Billion (another web site gives a value of 140 B.
1900 Galveston hurricane. 99.4 B. Another web site gives a value of 92 B.
2005. Hurricane Katrina.  81 B.

23). Number of major hurricanes in one season in the Atlantic.  8 in 1950.

24). Most active hurricane season ever for continental USA.  7 land-falling hurricanes in 1886.

25). Most active typhoon season ever in northeast Pacific.  27 in 1992.

26). Most active typhoon season ever in the North West Pacific. In 1964, a total of 39 tropical storms, out of which, 13 remained as tropical storms, 19 developed into typhoons and 7 intensified into super typhoons.

27). Deadliest hurricanes in the USA .  A hurricane hitting Galveston (Texas ) in 1900 caused a loss of life estimated to be between 8,000 and 12,000. The 1928 Florida Hurricane caused loss of life 2,500 to 3,000. Katrina of 2005 caused loss of life of about 1,500.

28). Most intense hurricane to ever strike USA .  Florida Keys in 1935 at category 5 had a central pressure of 892 hpa. Hurricane Camille in 1969 at category 5  had a central pressure of 909 hpa. By comparison, Katrina of 2005 at category 3 had a central pressure of 920 hpa.

29).   Earliest hurricane ever in north Atlantic was on 7 March in 1908(Noting that the hurricane season in the Atlantic is from 1 June to 30 November).
30). Latest hurricane ever in the north Atlantic was on 31 December 1954. TC Alice persisted until 5 January 1955.

31). Earliest date in the season for a hurricane to strike USA . Alma  on 9 June 1966.

32). Latest date in the season for a hurricane to strike USA . Near Tampa , Florida on 30 November 1925.

33). Largest number of hurricanes in the Atlantic at the same time 4 on 22 August 1893 and also on 25 September 1998.

34). Highest ACE (Accumulated Cyclone Energy) for a single storm in the Atlantic was 73.6 from Hurricane San Siriaco in 1899.

35). Season with the highest ACE in the North West Pacific. No value was given, but the web sites mention that it is the highest ever. The web sites mention 2nd highest ever was in 1992, but no value was given. The 3rd highest was in 1997 with a value of 594.1. From this one may deduce that the highest value in 1965 could be about 600. By comparison, the season in 2005 in which Katrina occurred had an ACE of 248, which is less than half of the highest seasonal ACE ever on the globe in 1965.

36). Farthest latitude ever reached by a TC.  Hurricane Faith in 1966 reached up to 62.5 deg N.

37). Farthest latitude at which a tropical storm intensified into a hurricane.  An un-named typhoon in central Pacific in 1975 it was a storm at 32 deg N. and became a hurricane at 40 deg N.

38). Maximum number of TC in one season in the north Indian Ocean.  10 in 1893, 1926, 1930, and 1976.

39). Minimum number of TC in one season in the north Indian Ocean.  1 in 1949.

40). Strongest horizontal pressure gradient. 5.5 hpa per Km in Hurricane Tracy near Darwin , Australia on 24 December 1974. Also 5 hpa per Km in Hurricane Inez in north Atlantic on 28 September 1966.

41). Highest wind wave generated by a TC.   34 m in North West pacific during 6th to 7th 1933. Also 25 m on 26th September 1935 in North West  Pacific.

42). Strongest wind gust in a TC.  78 meters per second at Chetumal , Mexico , on 28th September 1953. There might be a mistake in this value given by the web site of the Australian Bureau of Meteorology (Bureau of Meteorology Research centre). Usually the wind gust should be greater than sustained wind speed.  This record value for wind gust quoted here is less than the record for the maximum sustained wind speed of 85 m per sec for typhoon Tip. 43). Largest eye. TC Kerry in the Coral Sea on 21 Feb 1979 had an eye radius of 90 Km.

44). Smallest eye.  Hurricane Tracy on 24 December 1974 near Darwin, Australia had an eye of radius 6 Km.

45). Warmest eye at 700 hpa level.  30 deg C for super typhoon Nora in 1973 in North West pacific.

46). Warmest eye at 500 hpa level.  16.6 deg C for super typhoon Marge in August 1951 in North West Pacific.

47). Maximum vertical motion in a TC.   25 to 35 meters per second in TC Hilda in the Coral Sea  on 1 March 1990.

48). Most warnings ever issued for a TC.  79 for typhoon Rita in 1972 in North West Pacific. This typhoon lasted for 20 days.

49). Most damage from a TC at one location.  24 December 1974 at Darwin , Australia  from Hurricane Tracy . More than 80% of all homes in Darwin and vicinity were completely destroyed.

50) Maximum rubble ever piled up by a TC.  The storm surge and wind waves from Hurricane Bebe on 21 October 1972 at Funafuti Atoll (8 deg S, 179 deg E) raised a permanent rubble rampart 18 Km in length, 37 m in width and 3.5 m in height.

51). Best ship observations ever made of the surface structure of a TC.  Caught in a typhoon in North West Pacific, on 26 September 1935, officers of the Japanese Imperial navy collected the first and possibly still the most comprehensive set of observations.

52). Hot air produced from a TC.  A localized region of extremely warm Stratospheric air with 240 hpa temperature anomaly of 18 deg C attained over a distance of 13 Km at the end of a cloud band outside the eye of TC Kerry in Feb 1979 in the Coral sea, was measured by a Meteorologist in the cockpit of a Boeing 747 Jet liner and caused a major scare as the jet engines lost substantial power. In a similar incident, on the same day, in Western Australia, a jet liner descended to 3 Km altitude, before re-gaining engine power.

53). Year in which maximum number of tropical cyclones affected the east coast of India. 1922 with a total of 5.

54). Year in which maximum number of tropical cyclones affected the west coast of India was1908 with a total of 2.

55). Accumulated Cyclone Energy. How it varied between 1979 and 2009 (From the blog of Prof. Pielke Jr. ).

* US National Weather Service
* Hurricane Research Center, Miami, USA
* Atlantic Oceanographic and Meteorological Laboratory, USA.
* Australian Bureau of Meteorology.
* India Meteorological Department.
* SAARC (South Asian Association for Regional Cooperation), Meteorological Research Center, Dhaka, Bangladesh.
* Florida State University
* Bangladesh Meteorological Department
* National Oceanic and Atmospheric Administration, USA
* .World Meteorological Organization, Geneva.
* National Ocean Survey, USA.
* Hong Kong Observatory…
* Regional Meteorological Center-New Delhi, India.
* Inter-Governmental Oceanographic Commission of UNESCO, Paris, France.
* Bureau (Australian) Meteorological Research Center, Melbourne.
* Meteorological Services of Canada.
* U.K. Meteorological Agency
* Meteo France
* Indian Institute of Tropical Meteorology, Pune.
* Louisiana State University, Baton Rouge.
* National Institute of Oceanography, Goa, India.
* Joint Typhoon Warning Centre, Guam.
* CSIRO Marine & Atmospheric Research Laboratory, Hobart, Tasmania.
* WMO Regional Specialized Meteorological Center, Tokyo Typhoon Center, Japan Meteorological Agency.
* Fiji Meteorological Service, Nadi.
* China Meteorological Agency.
* Korea Meteorological Agency.
* Korea Ocean Research Development Institute, Ansan.
* Department of Meteorology & Hydrology, Myanmar.
* Department of Meteorology, Sri Lanka.
* Pakistan Meteorological Department.

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