Climate Change is Increasing the Likelihood of Worst-Case Scenarios

Featured Image: Hurricane Delta shortly before making landfall over the Yucatan Peninsula (2020). Image Credit: CIRA/RAMMB.

K. T. Bhatia, Vecchi, G. A., Knutson, T. R., Murakami, H., Kossin, J., Dixon, K. W. & Whitlock, C. E. (2019).  “Recent increases in tropical cyclone intensification rates.”  Nature Communications, 10.

Why is rapid intensification such a problem?

Hurricane forecasting has actually come a long way in the last few decades.  Track forecasts, or predictions of where hurricanes will go, have appreciably improved, but one outstanding difficulty is the question of how fast the hurricane wind speeds will be.  Rapid intensification is especially scary because it involves an abrupt increase in the strength and danger of a hurricane, while also being exceptionally difficult to forecast.  Meteorologists with whom I’ve spoken worry quite a bit about what they call the worst-case scenario, which is that a hurricane could undergo rapid intensification right before landfall, leaving those on the ground unwarned and unprepared for a dangerous natural disaster.

Flooding after Hurricane Harvey. Image Credit: AP Photo/David J. Philip.

Even though rapid intensification is relatively uncommon, it still has an outsized impact on the climatology, or statistics, of hurricanes.  Most Category 4 or 5 hurricanes reached their strength by undergoing rapid intensification at least once during their lifetime.  Hurricane researchers broadly agree that hurricanes will become more intense as a consequence of global warming (meaning there will be a greater frequency of Category 4 or 5 storms in the future), which leaves many of us to wonder if rapid intensification will become more common, too.

Earlier this year, Hurricane Laura also underwent rapid intensification before making landfall in Louisiana, not far from where Delta is forecasted to make landfall today. Image Credit: Wikipedia/NOAA.

How will climate change affect rapid intensification?

Since satellite technology only came into widespread use in the 1980s, we don’t actually have that many years of data on hurricanes.  This lack of data makes it difficult to spot trends because there’s a poor signal-to-noise ratio, meaning that random variations and short-term oscillations swamp out the signal from climate change.  This has motivated a number of researchers to address the climate change question by conducting modeling studies, or computer simulations, to forecast hurricanes under changing climate conditions.  Unfortunately, the answer that is emerging from this body of work appears to be that yes, rapid intensification will become more likely as the oceans warm and provide more fuel for hurricanes to intensify.  Even more worryingly, a 2019 study by Kieran Bhatia et al. suggests that climate change is already here: in defiance of the conventional wisdom that we haven’t been taking data very long, a trend in increasing intensification rates is already starting to stand out from the noise.

Left to right: Hurricanes Katia, Irma, and Jose (2017).  Hurricanes Irma and Jose, and soon after Hurricane Maria, all underwent rapid intensification.  Image Credit: Wikipedia/NOAA View Global Data Explorer.

To differentiate between the signal (i.e., changes due to climate change) and the noise (i.e., random or internal variability), the researchers used a combination of hurricane observations and very high-resolution climate models.  In order to gauge what the effects of noise should look like, the researchers ran the climate model under a scenario in which there was no anthropogenic climate change, but there was internal noise and variability.  Then they compared the simulated intensification rates of the hurricanes in this model to what we observe in real life.  Compared to the model, observed hurricanes in the Atlantic have been starting to intensify much more rapidly in the last 40 years.  

The researchers urge caution – not all sources of internal variability may have been captured by the model, and more years of data would strengthen our certainty in their conclusions.  However, they also emphasize that, according to their results, the observed increase in hurricane intensification rates cannot be explained solely by internal variability and noise.  Which is to say: odds are that we are already observing the signal — the impacts of climate change.

So where does this leave us?

Although this post is about hurricanes and rapid intensification, climate change is affecting severe weather and natural hazards of many forms.  One of the most concerning things about climate change is how it impacts the tails of distributions, or extreme events that are both very damaging and (formerly) very unlikely.  From droughts to floods to fires, extreme events are becoming more likely as a result of climate change.  And as 2020 has shown us, disasters never quite operate in isolation, but rather project onto and exacerbate existing injustices and inequalities.  “Everywhere you look,” says climate justice writer Mary Annaïse Heglar in a recent essay, “there’s some calamity wrapped in a tragedy inside an injustice – like nesting dolls.”

I think it’s really natural to feel overwhelmed (I do!) in the face of how much work we have to do.  One of my favorite descriptions for that feeling comes from a climate scientist named Raymond Pierrehumbert, whom I once heard refer to our current situation as “humanity’s final exam.”  As a student who’s definitely had to get through that anxiety spiral of not wanting to start studying for a test because I thought I’d fail anyway, I thought this was a really resonant metaphor.  We may not get 100% on our exam, but that doesn’t mean our efforts are wasted.  Every step we take and every degree of warming we prevent will save millions of lives.

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Rohini Shivamoggi

I'm a PhD student studying atmospheric sciences at MIT. I study the formation of secondary eyewalls in hurricanes, which hopefully will help us improve our forecasts of hurricane intensity. Before I got to MIT, I grew up in Florida and studied Chemistry and Physics at Harvard University. My other interests include weather forecasting, photography, and encouraging diversity in STEM! You can find me on Twitter @RShivamoggi.

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