The countdown is on: El Niño is coming. In the next year, this phenomenon will increase the risk of flooding in Peru, increase torrential rains in California, dry up Indonesia and impoverish the fisheries off Chile. In their crystal ball, some climatologists foresee a very powerful episode; others think it is too early to predict its intensity. One thing is certain: the burning association between El Niño and global warming will drag the world towards new temperature records.
In mid-May, the World Meteorological Organization (WMO) spoke from Geneva. “A warm El Niño episode is expected to develop in the coming months which, combined with human-made climate change, will push global temperatures into uncharted territory,” said Petteri Taalas, the Secretary General of WMO. “This will have far-reaching implications for health, food security, water management and the environment,” he added.
For the past three years, a major episode of La Niña — the enemy sister of the Niño — has tended to slightly contain the rise in atmospheric temperatures by injecting more heat into the ocean. The world thermometer still recorded temperatures 1.15°C higher than those of the 1850-1900 period. This moment of respite ended last March with the fainting of La Niña. The WMO now says it is virtually certain that the world temperature record set in 2016 (+1.28°C), during the last “super El Niño”, will be beaten within five years.
What will be the power of the enfant terrible who is currently preparing his weapons? “Hard to say,” replies American climatologist Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies. This spring saw a “rapid” and “very, very clear” warming of the ocean off Peru. “Because it’s developed so fast, people are saying it’s going to be a very strong El Niño. But for the moment, according to the statistical and dynamic models, the range of possible answers is still very wide,” he explains in French in an interview. “In a few months, it will become clear. »
A complex mechanism
The El Niño phenomenon returns at relatively regular intervals, every two to seven years. Each episode, which typically lasts 12 to 18 months, begins with the slowing of the trade winds, winds that blow westward in the tropical zone of the Pacific Ocean. Normally, these trade winds push the surface water found along the coast of Peru offshore. It follows, by suction effect, an upwelling of deep waters near the continent which is accompanied by a significant supply of nutrients – for fish (and fishermen), a feast!
When the trade winds slow down, El Niño kicks in. Near the continent, the upwelling of cool waters stops and the surface temperature of the ocean increases under the tropical sun. Above this superheated pool, warm, humid air rises skyward, bringing heavy downpours to southwestern South America. Also, the rising air has to come down somewhere. Once in the upper atmosphere, it slides to higher latitudes — 30° north and 30° south — and then disrupts jet streams (jet streams) that bring rain and shine elsewhere in the world.
Among the most recurrent long-range effects of the El Niño phenomenon—effects that climatologists aptly call “teleconnections”—let us mention the reduction of precipitation in Indonesia and northern South America, as well as excess rain in East Africa and the southern United States. These weather hazards destroy crops and flood cities. In Canada, an episode of El Niño can tend to milden the winter in the west of the country. However, the phenomenon has very few consequences in Quebec.
Reaching 1.5°C with El Niño
On a planetary scale, episodes of El Niño cause the mercury to rise slightly. Since, during these events, the upwelling of deep, cold Pacific waters slows down, less heat can be absorbed there. The atmosphere must take a little more on its shoulders. A medium-intensity El Niño event pushes the global thermometer up about 0.06°C, Schmidt said. If such an episode materializes by the end of the year, we can already predict that many temperature records will be shattered in 2024.
“The next few years are likely to be really hot because of El Niño which is resurfacing and which has a good chance of being strong,” observes climatologist Philippe Lucas-Picher of the University of Quebec in Montreal. It’s very solid scientifically. Within five years, we will probably approach the 1.5°C rise that we have been talking about for years. This symbolic mark will first be reached temporarily, the time of an episode of El Niño, before being reached definitively, a few years later, due to the accumulation of greenhouse gases in the atmosphere. .
At this time, scientists do not know if climate change alters the waltz between El Niño and La Niña. “It’s a chaotic system, very rich, very dynamic, and therefore it’s difficult to see a trend there,” explains Mr. Schmidt. Climatology over the past 40 years suggests that La Niña is taking over, but forecast models suggest the opposite. “Even if there is a small tendency linked to the forcing [climatique]the phenomenon will have roughly the same natural variability.