At some point during this season’s particularly burly winter, you may have found yourself wondering: what happened to global warming?
A third of the country saw near all-time record lows with the arrival of the “polar vortex” which plunged the Midwest into a particularly deep cold.
Turns out that this winter may have been triggered by climate change induced factors from all the way down in the tropical West Pacific, according to a new Insights article, published May 22 in the journal Science.
We broke down Oxford climate physicist Tim Palmer’s recipe for a cold Midwest winter into three simple steps.
Palmer likens getting a cold winter in a warming world to pulling a black card from a deck. The catch being that as the climate warms, the black cards are disappearing. Still, these frigid and terrible winters can happen. Here’s how:
Step One: Stir up the jet stream
Local weather conditions are heavily influenced by the Northern Hemisphere jet stream, a river of air that zips around miles above Earth’s surface. This stream is not a straight line, but moves along in ripples or waves, as you can see in the GIF above.
“Regions above which the jet stream is flowing from the north are likely to experience cold weather. Conversely, in regions above which it flows from the south, the weather is likely to be relatively warm,” wrote Palmer.
The bigger these ripples or waves are, the stranger our weather gets. The size of these ripples is partially controlled by how much energy the stream can commandeer. Crudely put, when certain areas become warmer, that excess heat can push a wave into the Jetstream.
Step Two: Add heat
Western Tradewinds have increased across the tropical Pacific, triggering ocean currents that draw heat from human-made greenhouse gases deep into the ocean. This has caused a slowing in global temperature rise since 1990. Some called it the global warming “pause.”
But these intensified trade winds have actually caused a warm water “pile up” in the waters of the tropical West Pacific, an area of the world known to have a large influence on global climate.
Man-made local warming contributes a comparatively small amount of heat to the warm water pile up. But, that little bit of heat seems to have been enough to tip the system over the edge.
Typhoons can be built from this excess heat. “Consistent with this, there was a very active typhoon season over the tropical West Pacific in 2013,” wrote Palmer. Typhoon Haiyan, which devastated the Philippines last November, was among the strongest tropical cyclones in recorded history.
This heat can also push the jet stream creating a large wave. In the case of this last winter, the heat bent the stream to just the right size and position to leave regions like the Midwest in prime position to receive cold weather from the Arctic — namely what we called the “polar vortex.”
This isn’t the last we’ve seen of these weird-weather anomalies.
Step Three: Add El Niño
Studies indicate that the warm phase of El Niño is on its way, which will weaken the trade winds. Weakening trade winds will mean the climate change “pause” may be coming to a close and temperature rise will speed up again.
Goodbye cold Midwest winters, at least for a little while.
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