Climate change could stoke super El Ninos
UNITED STATES: Even if we meet our most ambitious climate goal - keeping global temperatures within a strict 1.5 degrees Celsius of their preindustrial levels - there will still be consequences, scientists say. And they’ll last for years after we stop emitting carbon dioxide into the atmosphere.
New research suggests that extreme El Nino events - which can cause intense rainfall, flooding and other severe weather events in certain parts of the world - will occur more and more often as long as humans continue producing greenhouse gas emissions. And even if we’re able to stabilise the global climate at the 1.5 degree threshold, the study concludes, these events will continue to increase in frequency for up to another 100 years afterward. The findings were published yesterday in the journal Nature Climate Change.
‘‘It was really a surprise that what we find is after we reach 1.5 degrees Celsius and stabilise world temperatures, the frequency of extreme El Nino continued to increase for another century,’’ said Wenju Cai, a chief research scientist at Australia’s Commonwealth Scientific and Industrial Research Organisation and one of the new study’s lead authors. ‘‘We were expecting that the risk would stabilise.’’
The study builds on a 2014 paper, also published in Nature Climate Change by Cai and a group of colleagues, which first suggested that extreme El Nino events will increase with global warming. That paper focused on a business-as-usual climate trajectory, in which greenhouse gas emissions remain at high levels into the future, Cai noted. It found that under this scenario the frequency of extreme El Nino events would double from their preindustrial levels within this century.
The 2014 paper produced mixed responses among scientists at the time.
Some experts, including Kevin Trenberth of the National Centre for Atmospheric Research, suggested the models they used may not accurately simulate the behaviour of El Nino.
Nevertheless, after the Paris climate agreement was finalised, and the 1.5 degree temperature goal was established, the researchers were interested in revisiting their previous work. This time, they specifically investigated the way El Nino would be affected if the world actually managed to stay within this climate threshold, a target that many scientists believe is already close to slipping through our fingers. Recent research has suggested that we’re on track to overshoot this climate goal within the next few decades.
The researchers used a collection of 13 climate models to simulate a scenario in which global carbon dioxide emissions peak around the year 2040 and then decline, a trajectory which would keep the world within the 1.5 degree threshold. They then took note of how frequently these extreme events occurred in the simulations.
The models suggested that by the time we hit the 1.5 degree mark, the frequency of extreme El Nino will have doubled from its preindustrial level of about five events every 100 years to about 10. This increase will occur steadily over time, the researchers note, meaning that any additional increase in carbon dioxide in the future will lead to an increased risk of an extreme event.
This effect does increase slightly under stronger climate scenarios - the researchers report that under a 2-degree climate threshold, the increase in frequency is a bit stronger. But overall, each scenario produces approximately double the preindustrial frequency during this century, even if the effect is a bit larger under more severe trajectories.
This is in keeping with the 2014 research, which suggests that under a business-as-usual climate scenario, the frequency of extreme El Nino events will also approximately double before the end of the century.
But the consequences won’t stop when we reach 1.5 degrees. The study suggests that the frequency of extreme El Nino events will continue to increase (although at a slower rate) even after global temperatures stabilise, potentially for up to another 100 years. These findings are less firm, since not all the models are capable of projecting beyond the end of the century. But several of them indicate that by the year 2150, the frequency will have grown to about 14 events per 100 years.
The researchers noted that the same results did not hold true for La Nina events, which often produce the opposite effects of El Nino. While previous research has suggested that more intense warming scenarios may lead to more frequent La Nina events as well, the milder climate trajectory in this study did not produce any significant changes.
- Washington Post