The North American heatwave shows how climate change will affect our weather

The record-breaking US Pacific north-west heatwave killed almost 200 people in early July 2021 after extreme temperatures hit the normally moderate region. — US National Aeronautics and Space Administration

In mid June, it rained over the western Pacific Ocean near Japan. There was nothing especially remarkable about this rain event, yet it made big waves twice.

First, it disturbed the atmosphere in just the right way to set off an undulation in the jet stream – the river of very strong winds in the upper atmosphere – that atmospheric scientists call a Rossby wave (or a planetary wave). Then the wave was guided eastwards by the jet stream towards North America.