Climate change and bomb cyclones: What do we know?

In the United States, December 2022 will be a memorable holiday season. The holiday of the “bomb cyclone” — a massive winter storm that has so far affected over 200 million Americans. It disrupted travel with at least 3,000 canceled flights, caused widespread power outages and plunged much of the country into dangerously cold conditions.

The brutal conditions brought to life the words of the poet Christina Rossetti:

“In the bleak mid-winter
Frosty wind made moan
Earth stood hard as iron,
Water like a stone”

Inevitably, there will be politicians who use events like winter storms to argue that global warming is not happening. Remember Sen. James Inhofe’s (R-Okla.) infamous snowball on the floor of the U.S. Senate? In the worldview of such politicians, a severe winter storm proves conclusively that humans do not cause planetary warming.

This worldview is wrong. Dangerously wrong. Falsely equating a ball of frozen water to “disproof” of global warming is a snowball of ignorance — a snowball that can grow inexorably, accreting conspiracy theories, influencing millions. Such scientific ignorance is every bit as harmful to U.S. citizens as the deep-freeze conditions of the December 2022 bomb cyclone.

It’s just as dangerous to claim perfect understanding — to assert that climate scientists fully understand the links between global warming and the frequency and intensity of bomb cyclones. I wish that were the case. It isn’t. Understanding those complex links is work that is still at the cutting edge of climate science.

So, what do climate scientists know with confidence about possible interactions between the changing climate and the behavior of severe winter storms?

In “As you Like It,” Shakespeare wrote this memorable line:

“All the world’s a stage, and all the men and women merely players.”

That’s an apt metaphor here. Climate is the grand planetary stage on which all weather plays out. The weather includes the storms, floods, droughts, heat waves and bomb cyclones — all are players on the climate stage.

This stage is gradually changing. Human activities have altered Earth’s climate, warming global-average surface temperature by nearly 2 degrees Fahrenheit over the past 150 years. A couple of degrees of warming might not sound like a big deal — but it is a big deal in the context of natural temperature changes over millennia.

While global-average surface temperature is a valuable number to track, the geographical patterns of climate change are of even more interest to someone like me. I study these patterns with colleagues around the world. Patterns have power. They help us to identify distinctive human “fingerprints” embedded in the noise of natural climate variability. Human fingerprints are ubiquitous. They are in the ocean, on land, in the atmosphere and in the changing seasons.

In thinking about global warming and bomb cyclones, one major question is how global warming affects Earth’s atmospheric circulation patterns. Circulation patterns are a key influence on extreme weather events. Some of the human fingerprints that climate scientists have identified — like changes in surface pressure patterns — are directly linked to changes in atmospheric circulation patterns.

Other evidence for atmospheric circulation changes is more indirect. In the Northern Hemisphere, the Arctic has warmed by four times the global average, reducing the temperature gradient between the warmer tropics and cooler Arctic. The strength of this temperature gradient influences atmospheric circulation patterns, and perhaps even the “waviness” of the jet stream. In turn, the meanderings of the jet stream can affect the southward transport of cold Arctic air masses in winter.      

The wintertime meeting of such frigid Arctic air with warm, moist air is one of the ingredients of a bomb cyclone. We know with confidence that human-caused warming is moistening Earth’s atmosphere, thus changing a component of the bomb. Experimenting with bomb components is unwise.  

Let’s get back to our theater metaphor. We have some bad weather actors on the climate stage. Actors like droughts, heat waves, floods and bomb cyclones, which can cause great harm. By burning fossil fuels and increasing levels of heat-trapping greenhouse gases, we’ve changed key features of the climate stage: the lighting; the height; the tilt of the floor. The idea that the weather actors would be blissfully unaware of these stage changes is not credible. The actors are changing their old lines. Behaving differently.

Going forward, we need to better understand links between human-caused climate change and the “bad weather actors” mentioned above. Some of this work already exists — but much more remains to be done.

Ultimately, our collective decisions will affect the climate stage, the weather actors on it and whether the unfolding play is a tragedy of the commons or has a better conclusion. We all get to write the ending.

Ben Santer is a climate scientist, a visiting researcher at UCLA’s Joint Institute for Regional Earth System Science and Engineering, as well as a John D. and Catherine T. MacArthur fellow. He was the lead author of Chapter 8 of the 1995 report of the Intergovernmental Panel on Climate Change (IPCC) and has been a contributor to all six IPCC reports.