In the last few years, teams of scientists have developed a consistent protocol for rapidly analyzing the influence of climate change on extreme weather events. Within a week of the disaster, reports have been available to inform the conversation about whether we can expect more events like it in the future.
But on Wednesday, we saw the first example of something new—an analysis published the event even happened. A group led by Stony Brook University’s Kevin Reed ran a very simple computer model experiment on Hurricane Florence—which isn’t due to make landfall until Friday—and quickly released the top-line results.
The rapid studies we’ve been seeing are done by examining the historical weather record to estimate how rare and extreme a given storm or heat event would be in that area of the globe. From there, climate model simulations are used to see if climate change is expected to change the frequency of that type of event.
Future-casting
In this case, there’s obviously no data available for a thing that hasn’t happened yet. Instead, the researchers focused on a much more limited question that is faster to answer: how does a warmer world change this storm?
In the counterfactual world where global warming never happened, it’s impossible to say if Hurricane Florence would even have been born. Even small changes can have complex consequences on the atmosphere, such that events would play out completely differently.
But that’s not the point. Since Hurricane Florence occurring in this warmer world, we can simply examine the effect of warmer temperatures.
To do this, the researchers took the current state of the world on Tuesday, dropped that into their model as a starting point, and pressed play to simulate ahead to Sunday. For a comparison simulation, they took those starting conditions and essentially subtracted out global warming. In this counterfactual world, the storm looks significantly different.
Hurricanes are fueled by energy from the evaporation of warm seawater, so it’s no surprise that warmer sea surface temperatures should give the storm a boost. The size of the boost in this case is pretty remarkable, though. The model analysis showed the real-world Florence dumping near the coast than it would in a world without human-caused warming.
Bigger and wetter
The basic scaling of rainfall with the increased moisture available in a warmer atmosphere means you expect to see at least a six-percent increase. Studies have shown that add-on effects can put that number in the neighborhood of 15 percent for storms like hurricanes, and one study estimated a whopping 38 percent increase for Hurricane Harvey, for example. Still, 50 percent is even greater, and the team has not yet shown what factors caused such a large increase in the model simulation.
The modeled hurricane clearly stays stronger when simulated under current-day conditions, but it’s also larger. The diameter of the storm is about 80 kilometers (50 miles) greater than in the cooler simulation, which would translate into higher storm surge flooding on the coast.
Team member Michael Wehner told Ars that the team is working to repeat this analysis with updated observations as the storm barrels down on the Carolinas, so we’ll get to see how similar the results are for each iteration. The researchers also plan to repeat their work after the storm and carefully compare with the “forecast” analyses. That will help show how useful this trial run of pre-storm analysis was.
For their part, the group behind the within-one-week studies explained Thursday that they won’t be providing an analysis of Hurricane Florence in the near future (for reasons ranging from complex historical data to swamped workloads). But they did comment on these pre-storm results, writing, “More analyses are needed to assess the robustness of this quick analysis, although the basic result that global warming increases the precipitation is a very robust one supported by observations and modelling studies.”
