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This figure shows the history of the tropical storms, hurricanes, and major hurricanes (Category 3+) in the North Atlantic derived from the analysis of the National Hurricane Center [1] archive copy at the Wayback Machine. Thick lines are 10-year moving averages. Also indicated are major milestones in the techniques used to identify and analyze hurricanes as reported by Neumann et al. (1999).

Long-term fluctuations are evident in all three records. These may be attributed both to natural fluctuations, such as the Atlantic Multi-decadal Oscillation, and artificial factors associated with changing methods and techniques of observation.

For more than half the record, it is likely that hurricanes were undercounted due to the failure of any trained observer to encounter the storm. Similarly, the intensity may be understated if no observer encountered the eye wall. The fact that hurricanes often obtain their strongest state in the open ocean only increases the possiblity that past storms were miscategorized, though hurricane reanalysis projects do attempt to estimate likely storm intensities. Symptomatic of this, only 5 of the 36 Category Five storms observed in the North Atlantic were reported prior to the use of aircraft in studying hurricanes. In contrast, the techniques used to study storms in the past (e.g. inferring wind intensity from pressure and/or size of waves) may also have overestimated some storm intensities (Emanuel 2000). For many purposes, only the record known since the availability of satellite imagery in the 1960s is considered sufficiently reliable for analysis. It should also be noted that only in the North Atlantic does any attempt at systematic records exist for periods earlier than the 1940s.

Despite the limitations reported above, some researchers have pointed to the recent increase in storm activity and similar changes in other basins as indicative of some significant form of climate change (Webster et al. 2005), and occuring in association with changes in sea surface temperatures (Emanuel 2005). However, it is not possible to definitatively attribute these change to global warming or any other factor. Models suggest that global warming will lead to a modest increase in storm intensity (Knutson and Tuleya 2004), but that scale of the changes expected as a result of warming in the 20th century would probably be impossible to detect with the existing records.

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This figure was prepared by Robert A. Rohde from published data and is made available under the Global Warming Art license.

Image from Global Warming Art

This image is an original work created for Global Warming Art. Please refer to the image description page for more information.

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References

• Neumann, Charles J., Brian R. Jarvinen, Colin J. McAdie, and Gregory R. Hammer (1999). "Tropical Cyclones of the North Atlantic Ocean 1871-1998". Historical Climatology Series 6 (2).
• Emanuel, K. A. (2000). "A statistical analysis of tropical cyclone intensity". Monthly Weather Review 128: 1139-1152.
• Knutson, Thomas R. and Robert E. Tuleya (2004). "Impact of CO2-Induced Warming on Simulated Hurricane Intensity and Precipitation:Sensitivity to the Choice of Climate Model and Convective Parameterization". Journal of Climate 17 (18): 3477-3494.
• P. J. Webster, G. J. Holland, J. A. Curry, H.-R. Chang (2005). "Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment". Science 309 (5742): 1844-1846.
• Kerry Emanuel (2005). "Increasing destructiveness of tropical cyclones over the past 30 years". Nature 436: 686-688.

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