Climate Change And This Winter's Crazy Weather

What role did climate change play in this winter’s US freezes, heat, and drought?

This winter, the eastern USA was hit by frigid cold weather, although at the same time, the western states (and most of the rest of the world) were relatively toasty.

[.....]

The jet stream plays a key role here. Jet streams are bands of fast-moving air currents about five to seven miles above Earth’s surface. The polar jet stream influences weather in North America, and in turn is influenced by changes in the Arctic due to human-caused global warming.

The Arctic is the fastest-warming part of the planet, in large part because sea ice is disappearing so rapidly. White ice is reflective, but dark oceans aren’t. When sea ice sitting on top of the ocean melts, the Arctic surface becomes less reflective, absorbing more sunlight, which in turn melts more ice in what’s known as a “positive feedback.” Because the colder Arctic is warming faster than the warmer area to its south (e.g. North America), the temperature difference between the regions is shrinking.

That temperature difference is a big part of what normally keeps the jet stream strong and moving in a straight west-east line. When it shrinks, that allows more and larger wobbles (waves) to form in the weakened jet stream. As a result, weather patterns can get stuck as those waves slow down in the weaker jet, and the weather systems can become quasi-stationary or “blocked.” Picture a river with a slower current having more and larger meanders than a faster flowing one.

Consequences: Drier West Coast, cold weather in the East

While this is a topic of active research and significant uncertainty, a 2018 study published in “Nature Communications” found additional evidence that the jet stream has become increasingly wavy over the past 50 years, to a degree unprecedented in the past 290 years, which “can generate more frequent mid-latitude blocking patterns and facilitate persistent periods of extreme weather.”

 So we can continue to expect the weird winter weather, or worse, and climate change advances.