On the heels of Harvey’s devastating romp across southern Texas, Florida prepares for the possibility of getting slammed by an even stronger hurricane, Irma. Here is a prediction: if Irma destroys the Florida coast, many climate profiteers will rush to blame it on manmade global warming – just as they did with Harvey.
Prior to Harvey, which made landfall as a Category 4 storm, the U.S. had gone a remarkable 12 years without being hit by a hurricane of Category 3 strength or stronger. Since 1970 the U.S. has only seen four hurricanes of Category 4 or 5 strength. In the previous 47 years, the country was struck by 14 such storms.
Nevertheless, the fake news about Irma is bound to come. However, there are perfectly natural variations that can entirely explain the observed tropical storms. These tropical cyclones only arise during the warm season because they need a sea surface temperature above 26 degrees Celsius (about 79 Fahrenheit). Given that, it only makes sense that global warming will lead to more intense storms, right?
Negative Feedback Balances Climate Change
Not so fast. There are many forms of negative feedback – that is, effects that diminish the processes that created them – involved in climate change. For example, when surface temperatures increase, water evaporates, and we see an increase in clouds in the lower atmosphere, which in turn contributes to a slight cooling of surface temperatures – a natural balancing act. These feedback mechanisms can rapidly cool the surface temperature once it exceeds a certain threshold. The various feedback systems, both positive and negative, by which the climate regulates itself aren’t entirely understood, but there is no simple relationship between global temperature and extreme weather.
History Doesn’t Support the The AMO is More to Blame for Harvey and Irma than Man-Made Global Warming Theory
Additionally, there exist historical reconstructions of tropical cyclone energy dating back to 1851, and the data does not show any clear warming trend. Instead, there is a distinct cyclical pattern with peaks and troughs. The activity peaked around 1890, 1960 and 2000 with lulls in-between. See figure below.
The AMO is More to Blame Than Global Warming
Obviously, such variation cannot be due to our greenhouse gas emissions; they must be entirely natural in origin. So what could explain it? Chemical engineer Michel de Rougemont has put forth an interesting hypothesis. He noted that storm activity waxes and wanes with what is called the Atlantic Multidecadal Oscillation (AMO). Most people have heard of El Niño. The AMO is a somewhat similar phenomenon in the Atlantic Ocean. It affects the sea surface temperature, and could, therefore, have an impact on storm formation. De Rougemont has found a near perfect correlation between the hurricanes and the AMO. See graph below.
While the exact mechanism underlying such a phenomenon is not yet identified, it is far less speculative to posit a causal connection between known climate cycles and extreme weather than to blame it on humans – especially given the historical data. If the theory is confirmed, this bodes well for climate prediction, as it could enable us to predict peak storm activity many decades in advance. Imagine being able to inform local governments in vulnerable areas that we know that the next peak in weather activity will be 25 years from now and that they better have proper storm protection finished by then. Now, that would be useful.