The possibility of a record-strength El Ni帽o climate pattern this year is raising alarm among climate scientists, who are watching Pacific Ocean temperatures closely. Even a weaker El Ni帽o on top of human-driven global warming could have sweeping consequences for the climate, ranging from coral reef bleaching in Australia to flooding in East Africa, and also cost the global economy trillions of dollars.
鈥淲e have enough climate madness going on elsewhere without adding an El Ni帽o to it,鈥� says at the University of Colorado Boulder.
El Ni帽o, which occurs when sea surface temperatures in the eastern tropical Pacific Ocean rise 0.5掳C above the long term average, arrived around two months earlier than usual in May, following an unusual streak of three La Ni帽a years. Historically, this cycle of surface temperatures 鈥� known as the El Ni帽o Southern Oscillation (ENSO) 鈥� shifts between the warm El Ni帽o state and the cool La Ni帽a state every two to seven years, with neutral years in between.
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In the years since the last strong El Ni帽o in 2015-16, the Pacific has accumulated record amounts of heat, both from global warming and from natural oscillations in the ocean, says at the US National Oceanic and Atmospheric Administration (NOAA). The switch to El Ni帽o means much of that heat comes pouring back out into the atmosphere. 鈥淭he lid is off on the ocean,鈥� he says.
All that heat has already begun to have some influence on global weather, with predictions that it could make 2024 the first year global average temperatures surpass 1.5掳C of warming. But the new El Ni帽o is still relatively weak. The extent of its influence, and the severity of the consequences for every continent, largely depends on how much stronger it gets.
According to the latest from NOAA, there is a greater than 90 per cent chance that this El Ni帽o continues through to February next year. Its strength remains more uncertain, but at NOAA says there is a greater than 50 per cent chance it will be in the 鈥渦pper echelon of strong category鈥�, and a 20 per cent chance it will rival the powerful El Ni帽os of 1997-98 and 2015-16. 鈥淲e could be in record territory,鈥� says Rosencrans.
The specific outcome depends on how high the sea surface temperature gets in the tropical Pacific Ocean, as well as how closely the atmosphere responds to that warming. 鈥淓NSO is like a dance between the ocean and the atmosphere,鈥� says McPhaden. 鈥淏oth partners need to be dancing to the same tune.鈥�
Generally, warmer waters weaken the easterly trade winds, which leads to more warming in the ocean. But despite the record amount of heat stored in the ocean, the winds haven鈥檛 slowed much yet, says McPhaden. 鈥淭here are lots of things that can dither that signal,鈥� he says.
Counterintuitively, one possible reason for El Ni帽o鈥檚 sluggish development so far might be due to climate change. DiNezio thinks warm waters in the western Pacific could be offsetting the impact of warmer eastern waters on the trade winds.
Whatever the cause, the longer it takes El Ni帽o to strengthen, the less likely it is that it will reach historic strength this year. We should know by September, says Rosencrans. 鈥淭here鈥檚 not a lot of months left for this event to grow into a monster,鈥� says DiNezio.
While a strong event could be disastrous, even a relatively weak El Ni帽o risks creating more extreme weather, says McPhaden. Due to human-driven global warming, 鈥渨hat might be a heavy El Ni帽o rain now becomes an extreme El Ni帽o rain,鈥� he says. The same is true of drought and heat.
El Ni帽o could also have consequences for ecosystems, such as causing coral bleaching in the Great Barrier Reef due to warmer waters. The Amazon is another worry. at Yale University is concerned drought conditions driven by El Ni帽o on top of climate change and deforestation could make for an especially bad fire season there. 鈥溑∈悠祍 have been ringing the bell for months,鈥� he says.
That said, El Ni帽o can have beneficial effects. For instance, it could bring much-needed rain to the Horn of Africa, where 32 million people have been made food insecure by crop failures due to an unprecedented drought and years of conflict, says at the UN Food and Agriculture Organization. But too much rain could mean flooding, and to other parts of East Africa.
Overall, the coming El Ni帽o is likely to have a negative impact, says at Dartmouth College in New Hampshire. He and his colleagues have found the economic impacts of the climate pattern can be staggering, especially in poorer countries in the tropics. They estimate the very strong El Ni帽o of 1997-98 cost the global economy $5.7 trillion at the time.
Depending on how much carbon dioxide we continue to emit, Callahan鈥檚 team says the impacts of El Ni帽o in the 21st century could cause as much as a 5 per cent reduction in global economic output. With global warming in the mix, the potential consequences of an El Ni帽o of any strength are much more volatile, warns Callahan.
