Increase in Hurricane Activity Linked to Rising Ocean Temperatures

It has been acknowledged that Atlantic hurricane activity has increased a significant amount since 1995, but the question of course is: why? Thanks to Mark Saunders and Adam Lea of the Department of Space and Climate physics at the University College London, the answer is closer than before.

It is absolutely certain that Atlantic hurricane activity has increased since the 1980s. Based on the Accumulated Cyclone Energy index (ACE), the proportion of years with activity above the 1950-2000 mean has increased from 16% for the period of 1970-1994 to 82% for the period 1995-2005 (Saunders et al, 2008). This sudden rise in hurricane activity has two possible factors: sea surface temperature and an atmospheric wind field.

The purpose of Saunders and Lea’s study was to determine the contribution of sea surface temperatures alone. They collected several data: wind speed data, sea surface temperature (SST) data, monthly wind records, hurricane and tropical cyclone records, hurricane frequency models, and statistical models of sea warming. Through vigorous analysis, calculations, and interpretation, they removed the influence of atmospheric wind field and determined the following:

“Our results indicate that the sensitivity of tropical Atlantic hurricane activity to August–September sea surface temperature over the period we consider is such that a 0.5 °C increase in sea surface temperature is associated with a 40% increase in hurricane frequency and activity. The results also indicate that local sea surface warming was responsible for 40% of the increase in hurricane activity relative to the 1950–2000 average between 1996 and 2005.” (Saunders et al, 2008)

According to Saunders and Lea’s results, indeed warming sea surface temperatures are a significant contributing factor in increased hurricane activity; the results go further to prove that, in fact, even a 0.5°C increase in sea surface temperature can result in an alarming increase of 40% in hurricane activity.

However, the Atlantic hurricane activity has been interpreted as the result of two possible factors, one being rising sea surface temperatures linked to global warming trends, and the other, the return to the positive phase conditions of the Atlantic Multidecadal Oscillation (a naturally occurring oscillation of the North Atlantic Ocean). If indeed it is caused by only a natural occurrence, it is expected that hurricane activity levels will drop back down to normal within approximately 20 years. However, if linked to rising ocean temperatures caused by global warming, hurricane activity is expected to continue increasing through the twenty-first century (Saunders et al, 2008). Saunders addressing this, stating the following:

“Our analysis does not identify whether warming induced by greenhouse gases contributed to the increase in hurricane activity, but the ability of climate models to reproduce the observed relationship between hurricanes and sea surface temperature will serve as a useful means of assessing whether they are likely to provide reliable projections of future changes in Atlantic hurricane activity.” (Saunders et al, 2008)

Clearly, it is important to recognize that Atlantic hurricane activity levels are increasing significantly, and whether or not one wishes to address the issues of global warming, rising ocean temperatures should be a cause for alarm.

References

Saunders, M, et al. “Large contribution of sea surface warming to recent increase in Atlantic hurricane activity.” Nature. January 2008, 451, 557-560. doi:10.1038/nature06422.