How has climate change altered US heat extremes?

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Climate Change Has Made Extreme US Heat Waves "Virtually Impossible" Without Human Influence

A new study by the World Weather Attribution (WWA) group indicates that the current extreme heat and humidity affecting parts of the United States would have been "virtually impossible" without human-induced climate change. The research compared climate models of the world with and without human-caused heat-trapping emissions to assess the impact on recent heat events. This analysis highlights a significant shift in the likelihood and intensity of such weather phenomena due to global warming.
Increased Likelihood of Extreme Heat Events

In a hypothetical world without climate change, the extreme Wet Bulb Globe Temperatures (WBGT) observed during the recent heat wave would have occurred at most once every 5,000 years. This suggests that such conditions were vanishingly rare in pre-industrial times. The study's findings underscore the profound impact of anthropogenic emissions on increasing the frequency of dangerous heat conditions.
Current Conditions as a Rare Event

Even within the context of the current climate, influenced by human activity, these extreme heat and humidity conditions are estimated to be a one in 200-year event. While this still represents a rare occurrence, it is significantly more probable than in a world without climate change. The researchers noted a high degree of uncertainty in this estimation, given the exceptional nature of the event.
Role of Human Emissions and Heat Domes

The heat wave is primarily driven by a "heat dome," a high-pressure system that traps warm, moist air. Human-induced emissions have caused global temperatures to rise by approximately 2.5 degrees Fahrenheit (1.4 degrees Celsius) since before the industrial age. This background warming exacerbates the effects of natural weather patterns like heat domes, leading to higher observed temperatures, with daytime readings in affected areas topping 38 degrees Celsius.
Ruling Out Natural Variability as Primary Cause

Researchers specifically tested the influence of El Niño conditions, a natural climate phenomenon, on the current heat wave. Their analysis found that El Niño had only a minor cooling effect over northeastern North America, effectively ruling it out as the primary driver of the extreme heat. This further strengthens the conclusion that human-caused climate change is the dominant factor behind the intensity and likelihood of the observed heat and humidity.

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How has climate change altered US heat extremes?

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