A century's worth of records suggests that hurricanes are on the rise and a warming Atlantic is to blame

Using records dating back to 1855, hurricane researchers say they have uncovered an ongoing rise in the number of Atlantic hurricanes that tracks the increase in sea surface temperature related to climate change. Critics of such a link argue that this trend is merely because of better observations since the dawn of the satellite era in the 1970s. But the authors of the new study say the conclusion is hard to dodge.

"Even if we take the extreme of these error estimates, we are left with a significant trend since 1890 and a significant trend in major hurricanes starting anytime before 1920," say atmospheric scientists Greg Holland of the National Center for Atmospheric Research in Boulder, Colo., and Peter Webster of the Georgia Institute of Technology in Atlanta.

Update: You can read Holland and Webster's full paper here. [.pdf]. Chris Landsea (specialist with the National Hurricane Center) post a rebuttle here [.pdf] (interestinly enough, prior to the paper's release). Further discussion on both items can be found at Chris Mooney's blog, The Intersection.

More on this news item at National Geographic and New Scientist (UK). For further information, please see the links to the researchers' pages included above. Also, see Chris Mooney's recent book Storm World for more on the history of hurricane study, meteorology and climate science (my current reading).

[I'm going to be very strict in whatever I post here in the future. The public discussion for this seed is for related links and discussion of the science only. Non-related items, friendly or not, will be deleted unless relegated to a separate discussion. In other words, if you feel a need to comment on me or deny otherwise sound science, then clip this to some other group and start a new, private thread. Otherwise, your comment will be deleted. You have been warned. If you are in doubt, then don't post your comment.]

The government's ability to understand and predict hurricanes, drought and climate changes of all kinds is in danger because of deep cuts facing many Earth satellite programs and major delays in launching some of its most important new instruments, a panel of experts has concluded.

The two-year study by the National Academy of Sciences, released yesterday, determined that NASA's earth science budget has declined 30 percent since 2000. It stands to fall further as funding shifts to plans for a manned mission to the moon and Mars. The National Oceanic and Atmospheric Administration, meanwhile, has experienced enormous cost overruns and schedule delays with its premier weather and climate mission.

As a result, the panel said, the United States will not have the scientific information it needs in the years ahead to analyze severe storms and changes in Earth's climate unless programs are restored and funding made available.

Statements often appear in the media about suggesting that more extreme mid-latitude storms will result from global warming. For instance, western Norway was recently battered by an unusually strong storm which triggered many such speculations. But scientific papers on how global warming may affect the mid-latitude storms give a more mixed picture. In a recent paper by Bengtsson & Hodges (2006), simulations with the ECHAM5 Global Climate Model (GCM) were analysed, but they found no increase in the number of mid-latitude storms world-wide. Another study by Leckebusch et al. (2006) showed that the projection of storm characteristics was model-dependent. (Note that the dynamics of tropical and mid-latitude (often called 'extra-tropical') storms involve different processes, and tropical storms have been discussed in previous posts here on RC: here, here, here, and here).

The factors that control this are often confounding and so make this a tricky prediction. Simple arguments based on the expected 'polar amplification' and the fact that the surface temperature gradient between the tropics and the poles will likely decrease would reduce the scope for 'baroclinic instability' (the main generator of mid-latitudes storms). However, there are also increases in the upper troposphere/lower stratospheric gradients (due to the stratosphere cooling and the troposphere warming) and that has been shown to lead to increases in wind speeds at the surface. And finally, although latent heat release (from condensing water vapour) is not a fundamental driver of mid-latitude storms, it does play a role and that is likely to increase the intensity of the storms since there is generally more water vapour available in warmer world. It should also be clear that for any one locality, a shift in the storm tracks (associated with phenomena like the NAO or the sea ice edge) will often be more of an issue than the overall change in storm statistics.

Dr. Rasmus E. Benestad, a physicist and author at Real Climate, provides some detailed information on the complexities of climate change and how it affects tropical storms.

Anticipation of the 2006 hurricane season turned countless families here and in a vast swath of the Southeast into survivalists.

Households stockpiled ready-to-eat meals. They scarfed up emergency radios, propane stoves, satellite phones, shutters, candles, canned goods. Hordes plunked down $500 and up for home generators.

The predictions of another scary storm season and the memory of last year''s record-setting disasters inspired fear and a spending spree of hundreds of millions of dollars.

Since last year's devastating hurricane season, few issues have been more contentious than whether human-driven global warming is responsible for the increased intensity and frequency of these storms. Research reported online this week in the Proceedings of the National Academy of Sciences points the finger pretty directly, showing that human activities have warmed the oceans and thus helped breed stronger hurricanes.

Hurricanes are born in the warm waters of the tropical Atlantic and Pacific oceans, which are both getting warmer. Over the 20th century, ocean surface temperatures increased by between 0.32 degrees Celsius in the Pacific tropical region and 0.67 degrees C in the Atlantic tropical region. This has correlated with a twofold increase in category-4 and -5 hurricanes over the last 30 years. Some researchers maintain that these changes in sea surface temperature (SST) are within the natural variability of climate. Others say that the human-caused climate change is the culprit.

To figure out just how much people are to blame, atmospheric scientist Ben Santer of Lawrence Livermore National Laboratory in California and colleagues compared observed SSTs with the predictions of 22 global climate models. They ran the different models under various physical scenarios, including changes in solar irradiance, volcanic eruptions, and increased sulfate aerosols and greenhouse gas emissions. Only model simulations that included the known human-caused increases in greenhouse gases replicated the observed rise in SST. In total, the team found an 84% probability that two-thirds of the observed temperature changes were caused by human activities. There is no way of explaining the observed increases without positing a large human impact on these ocean temperatures, Santer says.

Emphasis added by me. I generally do not editorialize by highlighting sections of quotes such as this, but I find that the people who need to read that part the most seem to be the ones who never click on the link before leaving a comment.

Variously called hurricanes, typhoons or cyclones, depending on which ocean they form in, these storms rank among nature's fiercest. Huge, whirling tempests that form out at sea, tropical cyclones are assessed based on their strength in wind power. Those in the Atlantic are ranked on the Saffir-Simpson scale, developed in 1969 by scientists at the U.S. National Hurricane Center. The scale rates hurricanes by category [click here for the scale]. Even at their weakest, hurricanes generate winds in excess of 74 miles an hour. And stronger storms--such as last year's catastrophic Hurricane Katrina--wallop with winds greater than 131 miles an hour.

But despite the fact that tropical cyclones can release as much energy as 10,000 nuclear bombs, they spring from the same humble beginnings as any storm: a disturbance caused by converging winds. Atlantic hurricanes--named for Huracan, an evil deity of Central America's Tainos people--typically form when a thunderstorm blows off the coast of Africa, travels out to sea and gathers power over the eastern Caribbean. The storms, however, require high humidity, light winds in the upper atmosphere and warm seas to spin up to cyclonic strength. If one of these ingredients is missing, the storm will peter out.

It's no secret that 2005 was a ferocious hurricane season. A record 28 tropical storms and hurricanes--including four category-5s--lashed through the Atlantic, Gulf of Mexico, and Caribbean, leaving an appalling toll of death, misery, and destruction in their wakes. A new analysis shows that global warming was largely responsible for the number and intensity of the hurricanes. As global temperatures continue upward, we can expect more of the same, the authors warn.