Bringing up baby

IT IS a long way from the western Pacific Ocean to the flooded streets of Buenos Aires where, this month, the city’s Good Samaritans have been distributing food and candles by kayak after some unseasonably heavy rain. But there is a link. Its name is El Niño.

El Niño (Spanish for “The Boy”) is a Pacific-wide phenomenon that has global consequences. A Niño happens when warm water that has accumulated on the west side of the Pacific floods eastward with the abatement of the westerly trade winds which penned it up. (The long, dark equatorial streak on the map above, which shows sea-surface temperatures for August 10th-16th, indicates this.) The trade winds, and their decrease or reversal, are part of a cycle called ENSO (El Niño Southern Oscillation—see article).

The consequences of this phase of ENSO include heavy rain in south-eastern South America, western North America and eastern Africa, and drought in Australia, India and Indonesia. Another consequence, around Christmastide, is the sudden disappearance of the food supply of the Pacific anchoveta—and thus of the livelihoods of Peruvian fishermen. It was these fishermen who gave the phenomenon its name, the Boy in question being the young Jesus Christ.

El Niño-watchers at America’s National Oceanic and Atmospheric Administration (NOAA) noted worrisome ENSO-related changes in both sea temperature and air pressure earlier this year. They declared the return of the Boy in March. Australia’s Bureau of Meteorology decided to wait until May. Such forecasts can be wrong. Despite signs of the phenomenon last year, no monstrous event actually emerged. But during July the surface temperature of the central equatorial Pacific was almost 1°C higher than expected, and its equivalent in the eastern Pacific was more than 2°C above expectations. Among other things, that puts the temperatures in these areas well above the 26.5°C minimum needed for the formation of tropical storms. Right on cue, on July 12th, six such cyclones spun in the Pacific—more than on any previous day in over four decades.

Wet, wet, wet

Mike Halpert, the deputy director of NOAA’s Climate Prediction Centre, believes the current Niño could be among the strongest since records began in 1950. At the moment, the title is held by the one that straddled 1997 and 1998. This is reckoned to have killed 21,000 people and wreaked $36 billion of damage on houses, bridges and culverts. Such destruction could occur again if the trade winds relax still more, which Kevin Trenberth of America’s National Centre for Atmospheric Research reckons might happen in September.

That would pose problems to areas already too wet, such as Argentina. But it would also affect some dry places. In California four years of drought and huge wildfires have left the landscape vulnerable to damage by deluge. Precipitation onto the denuded land may well trigger mudslides and floods. Nor will the extra rain necessarily break the state’s drought, for the water will quickly find its way back to the Pacific. What California really needs is snow in the Sierras, where it will stay put, melt slowly, and thus replenish the reservoirs. But snow seems a remote possibility, thanks to the Pacific’s unusual Niño-induced warmth.

California aside, though, the United States tends to benefit from Niños. Increased Pacific storm activity is matched by decreased activity in the Atlantic. That means fewer hurricanes hit America’s east coast. The yields of farms in the Midwest improve too, thanks to milder weather. A recent study by Paul Cashin and Mehdi Raissi of the International Monetary Fund, and Kamiar Mohaddes of Cambridge University, cites the 1997-98 event as adding $15 billion to America’s economy.

Other countries, however, may be less lucky if this year’s Niño is a whopper. Indonesia could dry up, hurting coffee harvests and palm oil production (see article). Its hydroelectric-power supply might stall. And forest fires across its parched landscape would add up to 2 billion tonnes of carbon dioxide to the atmosphere (equivalent to 5% of worldwide human-related releases of the gas for the year), according to Simon Lewis of University College, London. Soyabeans in India, wheat in Australia and rice in China could also suffer. Between 1984 and 2004, according to a study published in May 2014, almost a quarter of the world’s harvested areas saw yields affected by Niño-related phenomena.

A Niño may also bring disease. In 1997 and 1998, heavy rain in Kenya and Tanzania created stagnant pools ideal for the larvae of malaria-carrying mosquitoes, and also, by damaging roads, made the distribution of drugs, insecticides and bed nets difficult. That could happen again.

One other consequence of a strong Niño may be to test the nature of recent climate change. A Niño’s rapid release of stored heat produces sudden global warming. It is, many climatologists believe, no coincidence that a recent apparent pause in global warming coincides with the quiet period since the last big Niño. There have been four sets of weak Niño-like conditions since 1998, but nothing full-blown—and between 1999 and 2013 the Earth’s surface temperature rose at a rate of just 0.04°C a decade, compared with the 0.18°C increase of the 1990s.

Truth or dare

Many of those sceptical of the extent of human-created climate change point to the pause as evidence of earlier rises being part of a natural cycle that has now peaked. Those who think human activities are changing the climate a lot believe excess heat has been sequestered during the pause, probably in the oceans, and is sitting there waiting to be released. Last year, for example, was the hottest in recorded meteorological history, a record assisted by the partial spilling, Niño-like, of the Pacific’s warm pool (even though no full-blown Niño developed). If ENSO does go the whole hog this time, it may be possible to find out who is right.