Some climate scientists have been unwilling to connect Climate Destabilization to the jet stream over the US getting wild-weather curvy, because there have been so few years to collect data. The Pacific North American teleconnection is a pattern of climate variability with positive (curvy jet stream) and negative (flat jet stream) phases. New evidence shows that a decreased equator to pole temperature gradient in the past resulted in the same pattern. It's now clear that the wild weather of warm Alaska and cold Eastern US in Winter isn't accidental.
The new study shows the jet stream pattern that brings North American wintertime weather extremes is millennia old -- "a longstanding and persistent pattern of climate variability," Bowen says. Yet it also suggests global warming may enhance the pattern so there will be more frequent or more severe winter weather extremes or both.
Human-caused climate change is reducing equator-to-pole temperature differences; the atmosphere is warming more at the poles than at the equator. Based on what happened in past millennia, that could make a curvy jet stream even more frequent and-or intense than it is now, he says.
The Pacific North American teleconnection, or PNA, "is a pattern of climate variability" with positive and negative phases, Bowen says.
"In periods of positive PNA, the jet stream is very sinuous. As it comes in from Hawaii and the Pacific, it tends to rocket up past British Columbia to the Yukon and Alaska, and then it plunges down over the Canadian plains and into the eastern United States. The main effect in terms of weather is that we tend to have cold winter weather throughout most of the eastern U.S. You have a freight car of arctic air that pushes down there."
The jet stream pattern -- whether curvy or flat -- has its greatest effects in winter and less impact on summer weather, Bowen says. The curvy pattern is enhanced by another climate phenomenon, the El Nino-Southern Oscillation... [emphasis mine]
For me this isn't all bad news. Cold winters where I live will help to prevent dengue from moving this far north, and help to keep tick populations from exploding.