Kategorie: News
Rising Sea Surface Temperatures in the Pacific
Evidence of a particularly strong El Niño is mounting. The temperature readings in the Pacific in May are particularly striking: several measurements exceeded previous records. While the direct consequences of extreme weather usually occur far from Europe, the effects are felt globally. There is already much talk of a possible “Super El Niño”—but a reliable assessment of the event’s strength cannot yet be made.
El Niño occurs irregularly, on average about every four years. The name comes from “El Niño de Navidad” (the Christ Child) and was coined by Peruvian fishermen who noticed the warming around Christmas and suffered economic losses due to the absence of fish schools.
The World Meteorological Organization (WMO) recently warned of the combination of ongoing warming and a possible El Niño episode: global average temperatures could reach record levels or come close to them over the next five years. The WMO currently estimates the probability of an El Niño phase developing between June and August at about 80 percent.
Persistently high sea surface temperatures in the tropical Pacific point to an emerging El Niño. Satellites show rising sea levels, indicating warmed, expanding water. Initial deviations in wind patterns also point to impending changes.
“It is fairly certain that we will see El Niño conditions in the tropical Pacific in the coming months. There are already signs, and these will intensify in the coming months,” explains Klaus Haslinger of GeoSphere Austria. He expects noticeable effects primarily starting in summer and fall; El Niño episodes usually peak between December and February.
Wind-Water Interaction
El Niño is one of the most important drivers of natural annual climate variability and influences precipitation and temperature patterns worldwide—with significant regional and seasonal variations.
In simple terms, El Niño (and its counterpart, La Niña) arises from interactions between ocean and air currents in the equatorial Pacific. Normally, trade winds blow from east to west, causing warm water to accumulate in the western Pacific and cold deep water to rise in the east. During El Niño, the Pacific warms significantly, and the trade winds weaken or shift eastward. Warm water spreads eastward and prevents the upwelling of cold deep water.
This can lead to drought in Australia and parts of Asia, while parts of the Americas face heavy rainfall. In the Atlantic, El Niño can dampen the development of storms due to changed wind conditions; in the Pacific, however, warmer water promotes the formation of strong tropical storms.
Indirect consequences reaching as far as Europe
Direct extreme weather events in Europe are rare due to El Niño. Nevertheless, indirect effects arise: crop failures in affected regions can influence global supply chains and prices.
In addition, the global average temperature rises during El Niño years—the British Met Office estimates the increase at about 0.2 °C. The additional heat released by the Pacific into the atmosphere can temporarily amplify the effects of global warming.
Strongest events to date and “Super El Niño”
Scientists do not formally use the term “Super El Niño,” but it is used in the media and, to some extent, among researchers when temperature anomalies are significantly higher than typical El Niño values. Haslinger: “If the temperature anomaly is significantly greater than in normal El Niño events, one might perhaps speak of a ‘Super El Niño.’” Whether that applies this time remains to be seen.
Strong El Niño events occurred around 1982/83, 1997/98, and most recently in 2015/16. During the particularly powerful event in 2016, the warming led to massive coral bleaching on the Great Barrier Reef—the most severe documented by James Cook University.
Frequency and duration vary; El Niño events occur roughly every two to seven years and usually last about a year. The name originates from Peruvian fishermen who observed the warming toward the end of the year and referred to it as “the Christ Child.”
Oceans as Heat Reservoirs
The oceans store the majority of the climate system’s excess heat—over 90 percent—and are warming as a result. Currently, sea surface temperatures are significantly higher than in previous years and are approaching historic highs; the average sea surface temperature has been above 21 °C in recent months.
Whether higher ocean temperatures will alter the frequency or intensity of El Niño in the long term remains a matter of debate among researchers. One thing is clear, however: in a generally warmer world, El Niño effects tend to be more pronounced.
Forecasting remains difficult
Sea temperatures can now be predicted fairly well; however, the atmosphere remains unpredictable. Air currents are volatile and difficult to forecast over the long term, so predictions for El Niño remain uncertain. Surprising twists are possible: In 2017, for example, a strong El Niño signal was predicted in the spring, which collapsed in the summer and was replaced by a La Niña phase, Haslinger recalls.
Small, not always measurable changes in the system can lead to major differences over the course of months. Currently, model forecasts for the temperature anomaly in the tropical Pacific range between approximately +1.0 and +3.5 °C. If the anomaly settles at the upper end of this range (around +3 to +3.5 °C), a very strong event—often referred to in the media as a “Super El Niño”—would be expected.