La Niña rides wave of cooling oceans
Think of it as Mother Nature’s roller-coaster ride: the shift between the weather patterns known as El Niño and La Niña that, at their worst, can cause havoc worldwide.
El Niño — spurred on by a warming of the equatorial Pacific — has dried up rice crops across Southeast Asia, cocoa fields in Ghana, coffee in Indonesia and sugar cane in Thailand since last year. It contributed to the Western Hemisphere’s strongest hurricane on record and the planet’s warmest year since at least the 1880s.
Now the ocean’s surface is starting to cool, which may signal the start of a La Niña. Scientists say this pattern typically contributes to more hurricanes in the Atlantic, drought in Brazil and heavy rain in Indonesia and India. While it might give a boost to U.S. natural gas, it could hurt Australian coal operations and palm-oil output in Malaysia. For some areas, it may be worse than a typical El Niño.
“El Niño extremes are greater, while La Niña lasts longer,” said Kevin Trenberth, distinguished senior scientist at the National Center for Atmospheric Research in Boulder.
The cycles occur every two to three years on average and help regulate Earth’s temperature as the equatorial Pacific absorbs the heat of the sun during the El Niño and then releases it into the atmosphere. That can create a La Niña: a “recharge state” when “the whole Earth is cooler than it was before this started,” Trenberth said.
Forecasters on two continents have issued La Niña watches for this year. Australia’s Bureau of Meteorology says the odds are about 50 percent. The U.S. Climate Prediction Center’s bet is 75 percent by December, but it says formation also could come earlier: sometime between July and September.
Peruvian fisherman centuries ago were first to notice the ocean would often warm late in the year. They called the phenomenon El Niño, after the Christ child. Modern researchers came to realize its importance to global weather in the 1960s, when they recognized the link between warm surface water and corresponding atmospheric changes. They tweaked the name to El Niño/Southern Oscillation. La Niña was named about two decades later.
The patterns aren’t simply opposite sides of the same coin. “La Niña is more like a strong case of ‘normal,’ ” Trenberth said. If a region is typically dry, it could become arid in a La Niña.
If it’s usually wet, there may be floods.
So far, the United States hasn’t tried to predict how strong a La Niña might be. For both parts of the cycle, greater intensity means greater impact. The ebbing El Niño was one of the three strongest on record, generating the hottest global temperatures in more than 130 years, according to the U.S. National Centers for Environmental Information in Asheville, N.C. April marked the 12th consecutive month to set a new record.
El Niño also spurred the growth of Hurricane Patricia last year, which clocked winds exceeding 200 mph before going ashore in Mexico.
La Niñas typically produce more hurricanes, but that may not mean more losses: What matters most is where the storms hit, according to Peter Hoeppe, head of Munich Re’s Geo Risks Research/Corporate Climate Center in Germany. And La Niñas actually have lowered the Atlantic hurricane count in some years by bringing more African sand storms — which reduce the moisture hurricanes need — and cooler water into the tropics, he said.