Strong El Niño continues to influence weather in the new year

The current El Niño phenomenon in the Pacific is probably about to reach its peak. According to the US weather agency NOAA, it could soon become a historically strong El Niño and last for months. This does not bode well for the year 2024.

A strong El Niño has already been developing in the tropical Pacific for months. According to the latest NOAA forecasts, there is a 54% probability that it will even exceed the threshold of a very strong or historic El Niño in the next two months. It will probably continue well into the first half of next year.

Due to the large area affected by significantly increased ocean temperatures and also because of its strength, El Niño can have a major impact on global weather in the coming year. Although this year's El Niño event is not quite as strong as the five strongest to date, such as the last event in 2015/2016, also known as the "Super El Niño", it is already one of the strongest El Niños observed to date and has already had a major impact on global weather in recent months, for example in the Amazon region or in Australia and Southeast Asia.

2024 could be the warmest year ever

El Niño also plays a decisive role in the enormous global temperature deviations of recent months. The warmest years in the past were almost always El Niño years and this is likely to remain the case even in times of accelerating global warming. 2024 is therefore likely to be one of the warmest or even the warmest year of all time globally, with all that this entails: droughts, heavy rainfall events and severe storms. Yet 2023 was already an absolute record year, according to the WMO, with a global temperature deviation of 1.4 degrees Celsius by the end of October.

In the northern hemisphere, El Niño influences the position of the jet stream over the Pacific and North America, among other things. For the USA, this often means stormier and, especially in the south-east, cooler and wetter periods, with sometimes severe winter spells. However, the shift in the jet stream can also affect Europe. The numerous storms in the fall, which mainly affected Western Europe, were a result of the exceptionally warm North Atlantic this year as well as the strong jet stream over the USA, some of which was located far to the south. The global atmosphere is also being enriched with additional moisture due to the high ocean temperatures in the tropical Pacific: heavier rainfall and flooding events are becoming more likely.

Dramatic situation in the Amazon

In the Amazon basin, the rainy season has long since begun. However, the drought there, which was mainly triggered by El Niño and intensified by global warming and deforestation, continued in December. Deforestation has been reduced by around 60 percent in recent months thanks to increased measures to protect the rainforest under President Lula da Silva. The delay in the rainy season caused by El Niño is having a major impact on the Amazon. The rainforest may already be approaching a tipping point postulated by some climate researchers. If it passes this point, large parts of the forest could inexorably turn into a drier, savannah-like landscape.

The Amazon is facing a deadly cocktail of several threats, all of which are contributing to its decimation: the El Niño phenomenon is causing an increase in high-pressure conditions with severe drought and heat. Global warming is also likely to have a similar effect, as it is also changing important air currents in the tropics, such as the trade winds. According to climate researchers, this alone is likely to make South America drier and thus increase the impact of El Nino. In addition, higher temperatures also increase evaporation, which, according to forest ecologists such as Professor Florian Wittmann from the Karlsruhe Institute of Technology (KIT), initially threatens the fringes of the rainforest in particular.

This is also where deforestation is particularly high, which represents the third threat with a similar effect. Deforestation on an industrial scale reduces evaporation and vertical movement because, as its name suggests, the rainforest creates its own climate through its dark, humid canopy. If it is cut down, it automatically becomes drier and hotter and the atmospheric circulation in the entire environment changes - eventually even on a global scale. This dangerous cocktail of global warming, deforestation and strong El Niños could soon push the rainforest beyond the tipping point assumed on the basis of climate simulations. With global consequences, because the Amazon is an important carbon sink - but only as long as it is moist.

Other factors influencing weather in Europe

In Europe, the direct effects of El Niño are significantly weaker and in some cases controversial. The temperature and pressure conditions in the North Atlantic, the Mediterranean, Scandinavia and the Arctic play a much more important role for the weather in Europe. This year, the exceptionally warm North Atlantic, which at times was up to one degree and regionally even up to eight (!) degrees warmer than ever before at the end of July, and the Mediterranean, which was also record warm in summer, were the main factors determining our weather. Their interaction was partly responsible for numerous record floods in the summer in the Alpine region, Slovenia, Spain, Greece, Libya and even Norway and Sweden.

The North Atlantic is still around half a degree warmer than ever before and has been responsible for the very high rainfall in Germany since July. It is speculated that there is a connection here with this year's record sea ice minimum in the Antarctic winter - the sea ice cover there is also still lower than ever before. The Antarctic is one of the main drivers of the infamous Atlantic Meridional Overturning Current (AMOC). If it slows down due to increasing meltwater inflows from the continental ice sheet and heat waves at the surface, which is already being observed, this could gradually lead to a build-up of heat at the sea surface. In addition, a sudden loss of the ocean's previous buffer function is possible, both in terms of heat and CO2. Unfortunately, no improvement is to be expected here either in the coming year, but further extremes.