World Cup heat, humidity in US 'virtually impossible' without climate change: study

WASHINGTON: Extreme heat and humidity affecting large parts of the United States during the World Cup and ahead of Fourth of July celebrations would have been virtually impossible without climate change, according to a study released on Friday by the World Weather Attribution group.

The research examined a heat wave linked to a strong heat dome, a high-pressure system that is trapping warm, moist air over much of the central and eastern United States as well as southern Canada. The study said such weather systems are common, but climate change is now making them produce higher temperatures.

Across many of the affected areas, daytime temperatures are rising above 100 degrees Fahrenheit, or 38 degrees Celsius, while humidity is making conditions feel even hotter. The researchers assessed heat stress using Wet Bulb Globe Temperature, or WBGT, an index they said gives a better measure of dangerous conditions than air temperature alone. Forecast WBGT readings are expected to reach record highs in much of the area covered by the study.

Using climate models, the researchers compared the present-day world shaped by human-caused heat-trapping emissions with a world without them. The study said those emissions have raised global temperatures by 2.5F, or 1.4C, since before the industrial age. It found that in a world without climate change, the forecast WBGT levels would have been so unusual as to be virtually impossible, occurring at most once every 5,000 years.

The study added that even under current climate conditions, the event remains exceptionally rare, estimating it as a one-in-200-year occurrence, while noting a high degree of uncertainty because of its severity. Researchers also tested whether developing El Nino conditions in the Pacific could explain the event, but found that its effect over northeastern North America was a minor cooling influence.

Imperial College London researcher Theodore Keeping, who co-authored the study for World Weather Attribution, said the findings underscored how much the country’s climate has changed.