In recent years, tropical storms, depressions and hurricanes dominated the news media like never before. Their intensity was stronger, their devastation, more widespread. Demolished buildings, power outages and deaths lay in their wake.
The impression exists that hurricanes will progress to do even greater damage in the future. Is this all simply impression based on emotional reaction? Or is there hard evidence – backed up by scientific data – to link the severity of hurricanes to the ongoing process of global warming?
Statistical Relationships between Global Warming and Hurricanes
Atmospheric scientists refer to a measure called the power dissipation index (PDI) when talking about hurricane activity in the Atlantic Ocean. The PDI factors in storm frequency, intensity and duration. Another highly relative statistic they consider is the SST, i.e. sea surface temperature. Although no premature assertions of causation are on the table, researchers do note that these two significant measurements are rising in tandem.
The relationship between increasing PDI and rising SST is not an ironclad fact. Yet. Still, there is plenty of climatologic smoke suggesting the presence of atmospheric fire. Establishing causation is a more complicated feat.
The trouble rests in the problematic presence of two SSTs. The Atlantic SST, when compared to hurricane activity, implies a strong connection between greenhouse gas emissions and heightened PDI. Yet relative SST – that is, the sea surface temperatures in the localized zone of the tropical storm – demonstrates a somewhat weaker link with power dissipation.
To be sure, a correlation is visible, but not as vivid or striking as with the broader Atlantic SST. Clearing up the discrepancy requires a larger scope of study, extending deeper into the past. Going beyond a 50 year window of history might yield some clues.
What does the historical record say about global warming and hurricanes? Stretching back to the late 19th century, some proportional relationship between climate change and hurricane severity is discernible. It was in the 1860s when a physicist named John Tyndall recognized the existence of a greenhouse effect and when Swedish researcher Svante Arrhenius determined carbon dioxide could significantly exacerbate it.
Dovetailing with the Industrial Revolution, extant records show an increasing trend in hurricane frequency and a rise in sea level temperatures. On the face of it, this fuels the theory of clear connection. While such events are difficult to write off as mere coincidence, the data does not prove direct influence.
One circumstance that prevents certainty on this issue is the spotty reporting of at-sea storms. Shipping lanes were far less travelled in the decades leading up to the 1880s, for example. Without satellite technology, hurricanes were only detected by witnesses. It stands to reason that there could have been many earlier offshore hurricanes that simply went sight unseen. Therefore, any ascending trend in tropical storms can, in part, credit improving powers of observation.
Limiting the research to hurricanes that make landfall reveals no uptick in frequency. So, the concept of greater historical context could close the deal in cementing the link between greater hurricane power and sea surface temperatures. The fact remains, nonetheless, that scientific observation was too limited to yield accurate data.
Computer Models on Global Warming and Hurricanes
Computer modeling more starkly underscores the strangely symbiotic relationship between global warming and hurricanes. In the 1960s, scientists began modeling climate changes from the pre-industrial era to the present. Calculating for humidity, cloud cover, water vapor and atmospheric convection, among other variables, they discovered that each component reacted when one element changed. They were able to quantify and map these reactions thereby allowing for projection into the future. In so doing, they could adjust one of the determinants and predict how the others would respond.
Using the dawn of the industrialization period as a starting point, models indicate that atmospheric CO2 increased by 50 percent. Global temperatures rose, on average, by one degree Celsius. The first climate model saw this coming. The question remains as to whether subsequent models are as accurate as the first one. If they are, towns, cities and nation-states will have to take stronger and more lethal hurricanes seriously, and plan accordingly.
The models, however, are not without critics, who point to dire predictions that are yet unrealized. While improvements in and tweaking of models are ongoing, few can dispute that technological illustrations have enjoyed some success. Present-day models forecast a continued climbing of SSTs and responsive uptick in PDIs.
Leaving computer models aside, hurricane watchers see unusual unfolding of these dangerous weather systems. One striking example is the slow movement – a stalling, in fact – of Hurricane Harvey over southern Texas in the early autumn of 2017. Climate activists have long contended that human activity is implicit in a widened high-pressure system over the southern United States. and a jet stream realigned to the north. Both of these phenomena, in turn, lessen the momentum for tropical storms to move through quickly. Hence, the storm sits atop a region, raining and raining…and raining.
Again, such slowdowns, with all of the disastrous flooding that ensued, could just be anomalies. To link global warming and hurricanes on the basis of atypical movement requires more time and study. Definite patterns might be there but they are as yet unidentified. In any case, hurricane trajectories and tempos are worth looking at. For many years, two giants in the philosophy of science argued over how to deal with anomalies. Are they explainable within a given theory or do they falsify it? The speed, direction and expansiveness of brutal storms reignites this dispute.
Evidence strongly suggests a relationship between global warming and hurricanes. But a causal connection between rising temperatures and hurricane ferocity is not yet confirmed. An important rule of thumb is to act on the compelling suggestion while relentlessly pursuing scientific truth. It might solidify the suspicions of climate activists. It might, on the flip side, undermine them. Either way, we have nothing to fear from honest inquiry.