It’s peak North Atlantic hurricane season again and much is being made of a supposedly increased hurricane threat due to man-made global warming.
It’s a contentious issue, to say the least. JunkScience.com has tried to slice through a little of the overblown rhetoric to see what, if any, cold, hard facts are available.
If you look at a graph from the Chronological List of All Hurricanes Which Affected the Continental United States: 1851-2005 compiled by the National Oceanic and Atmospheric Administration, the years 2004-2005 represent the only time in this relatively short record that there have been two consecutive years with more than four hurricanes making U.S. landfall.
This, however, does not constitute proof of global warming-enhanced, landfalling hurricane activity.
Since 1928 -- the mid-point of the period 1851-2005 -- there have been 134 landfalling hurricanes as compared to 145 landfalling hurricanes prior to 1928. So there’s actually been a significant decrease in hurricane frequency though global temperatures likely have warmed somewhat since 1928.
There also hasn’t been an increase in the number of stormy seasons. Pre-1928, there were nine years with three or more hurricanes compared to only five years with three or more hurricanes post-1928.
There appear to have been more category four and category five storms post-1928 as compared to pre-1928 (12 vs. 9). But since that difference depends on measurements of maximum hurricane wind speeds, it could easily be questioned given dramatic technological improvements in modern hurricane data collection.
Looking at the data by decade, it’s apparent that the anomalously quiet 1920s were followed by surging landfalling hurricane frequency in the 1930s and 1940s. But after the 1940s, the remainder of the 20th century was rather quiet.
The statistics for 2004 and 2005 may look ominous at first blush, but we have no way of knowing how the remainder of the decade will ultimately pan out. With annual landfalling hurricane counts of 0, 1, 2, 6 and 6 for the period 2001-2005, it could be a big decade -- or not.
The question originally posed, of course, was whether the increasing atmospheric carbon dioxide is associated with more or more-severe landfalling hurricanes. To answer this question, we plotted storms against atmospheric carbon dioxide levels.
Curiously, the post-World War II period of increasing fossil fuel use and associated increase in atmospheric carbon dioxide is concurrent with the most sustained lull in landfalling hurricane activity throughout the record. While this doesn’t disprove any association between global warming and landfalling hurricane frequency or intensity, it lends no support to the contention either.
It then strongly looks as though 2004-2005 was simply an unlucky anomaly since hurricane trends bear no similarity to the annual atmospheric carbon dioxide trend and, by extension, to global warming.
The last time there were 15 landfalling hurricanes in a four-year period was back in the 1880s. Even so, the entire 1880s ended up having only one or two more landfalling hurricanes than the preceding and subsequent decades. History, therefore, cautions us against jumping to rash conclusions about whether the opening decade of the Third Millennium will likely become a record-breaker. We'll have to wait and see -- but history suggests it's somewhat unlikely.
Finally, we’ve also plotted a new graph of global temperature data -- from the UK’s Hadley Centre for Climate Prediction and Research -- against atmospheric carbon dioxide data -- from Mauna Loa, Hawaii, the longest continuous record of atmospheric carbon dioxide concentrations available in the world.
The graph shows very little change in either global temperature or atmospheric carbon dioxide level since 1850. That’s because we plotted the ranges on scales that better suit planetary history as opposed to the global warming lobby’s fascination with dramatized illustrations of relatively small temperature change over short time periods. Temperatures are plotted in degrees Kelvin, the absolute temperature scale, and carbon dioxide levels are plotted in terms of their historical range, which has been more than an order of magnitude greater than current levels.
Has the planet warmed over the last two centuries? Almost certainly it has. But we can say with equal certainty that, from a planetary perspective, it hasn’t warmed very much and, when viewed on a more appropriate scale, nowhere near the “dangerous” levels claimed by alarmists. And no one knows with any certainty why the warming has occurred.
This is why the United Nations Intergovernmental Panel on Climate Change’s (IPCC) estimate of average global temperature change – 0.6 ± 0.2 degrees Centigrade during the 20th century – is really a trivial matter when viewed in the proper historical context. Simply put, a change in absolute planetary mean temperature of 0.2 percent is unlikely to have caused catastrophic climate change.