El Niño and global warming are mixing in alarming ways
AFTER YEARS of praying for more rain, Californians unexpectedly found themselves wishing for less this week, when tropical storm Hilary blew in from Mexico on August 21st. Rainfall records were smashed in Los Angeles and San Diego. Death Valley, farther inland, was deluged with as much rain in a day as it normally receives in a year.
Inundated roads completely cut off the nearby city of Palm Springs for a time. Hurricanes and tropical storms hit California only very rarely: none had even come close since 1997, and the previous one to make landfall was in 1939. Most of the few that have reached the state, however, including Hilary, have coincided with El Niño, a weather pattern that temporarily raises global temperatures while redistributing heat and moisture around the world.
Meteorologists predict that the current El Niño, which began in June, will be a strong one—perhaps as severe as the one that ended in 2016, which helped make that year the hottest ever recorded. If they are right, the record is almost certain to fall this year or next. “We are in uncharted waters," says Maarten van Aalst, director of the Dutch meteorological agency and former head of the Red Cross Red Crescent Climate Centre.
“We have never had an El Niño on top of so much global warming, so we don’t know what is going to happen." El Niños form and eventually dissipate owing to interactions between the trade winds that blow to the south of the equator and the ocean beneath them. The resulting accumulations of hotter- or colder-than-average water and high or low pressure in the atmosphere affect temperatures, winds and rainfall. Most of the time, the trade winds blow warm water from the central Pacific westward, towards Australia and Asia.
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