What causes a heat wave?
A heat wave is defined by the National Oceanic and Atmospheric Administration as a period of unusually hot weather that lasts two or more days. To be considered a heat wave, the temperatures have to be outside the historical averages for a given area.
They form when high pressure systems trap warm air in a particular area. This forces air to sink and compress, creating a dome of heat, which increases temperatures at the surface.
Why do heat waves seem to be happening more often?
Scientists have long understood that human-induced climate change would cause the Earth to heat up.
“We always knew that climate change was going to bring more extreme heat days, and that was going to start earlier in the year,” says Dr. David Eisenman, professor of medicine at UCLA whose research focuses on the public health impacts of extreme heat. “And I think we’re seeing that now.”
The trend has become especially apparent over the last few years. Global temperatures from the past three years averaged more than 1.5°C above the pre-industrial level, and the last decade has been the warmest on record. (One or two years of global temperatures above 1.5°C does not mean the world has passed the Paris Agreement goal to limit warming to 1.5°C. Scientists determine long-term temperature changes on timescales of decades.)
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