Hurricane Lorenzo has become a record-breaking storm and an odd one too. My Forbes colleague Dennis Mersereau wrote an outstanding piece summarizing the status of the storm. While the storm poses no immediate threat to land, it could approach the Azores and eventually the British Isles next week. Mersereau wrote on September 28th:
Hurricane Lorenzo rapidly strengthened into a scale-topping category five hurricane on Saturday evening, with maximum sustained winds reaching an incredible 160 MPH. This breaks the record for both the easternmost and northernmost category five hurricane ever recorded in the Atlantic Ocean
At the time of writing, it is still a strong category 4 hurricane. Inevitably, this storm will evoke questions about climate change so let’s deal with what we know without all of the hype and innuendo.
Where Atlantic Basin hurricanes first became category 5 intensity in the record-keeping era.
Why is the climate change question going to come up? University of Miami’s hurricane expert Brian McNoldy wrote in his blog, “Only about 2% of Atlantic named storms ever achieve Category 5 status." Phil Klotzbach also tweeted the graphic above illustrating where Category 5 storms first reached that intensity. Hurricane Lorenzo is the blue dot. The bottom line is that Category 5 storms are already rare, and Hurricane Lorenzo is unprecedented in the record-keeping era. We just don’t see hurricanes at this intensity so far east and north because water temperatures are typically too cold and wind shear conditions can also be restrictive. I am old enough to remember the old Sesame Street rhyme “One of these things is not like the other” and now I am humming it.
An examination of sea surface temperature anomalies (departures from average normal conditions) reveals that waters are anomalously warm in the region of Hurricane Lorenzo and its projected path. McNoldy writes, “The water under Lorenzo when it was a Category 5 hurricane is about 28°C (82.4), which is about 1°C (1.8°F) warmer than average... just enough to give it that extra jolt.”
Global Sea Surface Temperature anomalies as of September 29 (00z)
As I pointed out in a 2017 Forbes article as Hurricane Ophelia made its way to Ireland, a 2013 study published in Geophysical Research Letters found that climate warming should result in more hurricanes affecting Europe. They attributed this conclusion to relatively high-resolution climate model simulations that project that Atlantic tropical sea surface temperatures would extend eastward in the Atlantic Ocean. A “dream team” of some of the world’s top hurricane experts published a 2014 study in Nature pointing to a poleward shift in where hurricanes were strengthening. Their reasoning was related to shifts in potential intensity and wind shear structure in the atmosphere. Though Hurricane Lorenzo is only one data point, it is certainly consistent with these findings.
Projected path of Hurricane Lorenzo
Candidly, I find arguments affirming or refuting hurricane-climate change linkages based on 1-storm logic to be a bit tiring. It is important not to frame things in terms of “Was that storm caused by climate change?” because the cherry-picked rationales from all flanks will start popping up like weeds in a lawn. I prefer to use guidance from the NOAA Geophysical Fluid Dynamics website on hurricanes and climate change. The website is well-maintained, updated, and includes perspectives from the scientific literature rather than social media. Here are some key summaries from that website (Bookmark it):
- Sea level rise has a significant anthropogenic contribution and will mean more coastal inundation, on average, in tropical cyclones compared to past storms at lower sea levels.
- Tropical cyclone rainfall rates will likely increase due to warming and increased moisture. Folks, this is basic physics if you understand the Clausius-Clapeyron relationship and consider new studies showing that hurricanes are stalling or slowing down more frequently. .
- Tropical cyclone intensities and destructive potential per storm will increase globally, on average, but storm size relationships are more uncertain
- The proportion of storms that reach very intense (Category 4 and 5) levels is likely to increase as a result of anthropogenic warming over the 21st century, but there is less confidence changes in the number or frequency Category 4 and 5 storms. In terms of the number of storms of all categories, most models project very little change or a slight decrease. However, when they happen, on average, they are likely to be stronger."
This is not my opinion but what the best published science says.
Hurricane Lorenzo in the Atlantic on the morning of September 29th, 2019
Updated: An original post included a Tweet from Ryan Maue that has been removed.
