The Energy Transition Show with Chris Nelder

Millions of Americans are sweltering under heat domes this summer, with temperatures soaring to record highs when weather systems stall. The grid feels the strain of these events too. This extreme heat often creates a precarious situation that pushes electricity demand to levels never seen before, while forcing generation out of service. But why does summer weather get stuck like this in the first place? And is climate change making it happen more often? For answers we can look to the North Atlantic jet stream, the high-altitude wind steering weather across North America and Europe. Our guest visualizes this as a ski-slope, where a steep gradient between temperatures keeps the jet racing fast and weather moving. Though, as the Arctic warms faster than the rest of the planet, the slope flattens, slowing the jet stream, which has it meandering in bigger waves. Slow weather becomes stuck weather. Whatever comes along, heat, rain, or drought, can then sit around for longer. Our host Chris Nelder dug into this mechanism in Episode #65, the ninth part of our climate science miniseries. That was back in 2018, years before "heat dome" became a household phrase. In this conversation, recorded February 2018, Valerie Trouet, of the University of Arizona's Laboratory of Tree-Ring Research, explains how she reconstructed the jet's summer position back to 1725 from the density of tree rings in the British Isles and the Balkans. As the planet warmed, the jet lunged north and south far more often. Jet stream excursions like this have increased sharply since the 1960s, looking nothing like the natural climate variability of the three-century record. Valerie Trouet shares with us how a five-millimeter core from a living tree reveals the climate's history. She also covers why the jet's slowdown makes more of an impact than how far it swings. Valerie's lab has continued publishing on this topic, and in a 2024 paper in Nature, her group took the reconstruction back to 1300 CE, reading jet behavior in seven hundred years of European harvest dates, grain markets, and mortality. Her former postdoc went even longer in a 2025 study tracing hemisphere-wide jet patterns across a full millennium, and so far, their frequency looks essentially unchanged on that extended timescale. Today's episode is one of our lagniappe releases, so the complete original conversation can be freely available for the entire Energy Transition Show audience.

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