Why are the seas currently unusually warm?

The temperature of near-surface seawater is unusually high around the world. This is not only due to man-made climate change, but may also be due to a volcanic eruption in the South Pacific.

In the next few days, cold air of polar origin will reach central Europe via the North Sea, bringing the low mountain ranges their first winter greeting in the form of a few centimeters of fresh snow. Although flakes are also falling over the lowlands, wintry weather is likely to persist into next week at altitudes above about 500 metres.

The air mass remains about two to five degrees cooler than usual at this time of year, but this is still not enough for permanent frost in the lowlands. Although the temperature near the land ranges between 20 below zero and 15 below zero at the beginning of the journey off the eastern coast of Greenland, the air passes over the North Sea, which gets warmer towards the south, and then reaches the German coast, more moderate at about 2 to 4 grades.

Warm colors in all the world’s oceans

This is a completely normal process at this time of year, but North Sea waters in the German Gulf offshore are about one to three degrees warmer than usual at 11 to 14 degrees. This in itself is no cause for concern, but the near-surface seawater temperature in the Baltic Sea is also 0.5 to 2.5 degrees warmer than normal. Also in the Mediterranean region, the temperature level is usually one to three degrees higher than average during the years between 1971 and 2000.

Looking at global anomalies, warm colors prevail in all oceans around the world. Between 1982 and 2011, the global average near-surface water temperature at this time of year was 20.0 degrees. The lowest value was 19.7, the highest so far was 20.5, and currently 20.8 degrees. This thermal anomaly is not something that has been around since yesterday, as might be expected due to the thermal inertia of the oceans. This has been going on since March 2023 Unprecedented high temperatures were observed.

Effects of the El Niño phenomenon

Clues as to why can be found in the pronounced tongue of warm water, which runs along the equator from the coast of South America about 10,000 kilometers west to the Pacific Ocean. In this giant region of ocean, sea surface temperatures have been two to five degrees higher than normal for several months. These are the effects of the current El Niño phenomenon, a natural fluctuation in sea surface temperature that occurs in this region every two to seven years.

The last El Niño event, which lasted from 2014 to 2016, set records for global temperature and precipitation anomalies. Even in the wake of the current event, the impacts are global. In Brazil, for example, people are already experiencing unusual heat waves before the arrival of the Southern Hemisphere summer, and the Amazon rainforest is experiencing the most severe drought since records began more than 120 years ago.

Record value on November 17

Since large amounts of heat are released from the ocean into the atmosphere during El Niño, the global average temperature of the air layers near the Earth has also reached record levels. On November 17, according to the European Union’s Copernicus Climate Change Service, 2.06 degrees was recorded for the first time, a value more than two degrees above pre-industrial levels, that is, the average for the years 1850 to 1900.

This is a limit that, according to the United Nations Framework Convention on Climate Change, should not be exceeded on average for several years. Higher values ​​on individual days do not mean this limit has been exceeded, but this is an unambiguous warning signal.

Volcanic eruption in Tonga

However, the striking warming experienced in other large areas of the ocean, in the Atlantic and Indian Oceans, cannot be directly attributed to El Niño. On January 15, 2022, the Hunga Tonga-Hunga Haapai volcano erupted on the Pacific island of Tonga. As a result of the undersea eruption, as well as the cooling of sulfur dioxide aerosols, huge amounts of water vapor entered the stratosphere and were distributed globally in the following months.

Water vapor is a potent greenhouse gas and therefore has a warming effect. The element that prevails is the subject of the current research. However, no similar outbreak has been observed to date, so the impacts and duration on global mean temperatures and near-surface sea temperatures remain unclear.

In any case, the effects of global warming caused by human activities are becoming more certain. The oceans absorb up to 90% of the additional heat energy generated by increasing concentrations of greenhouse gases in the atmosphere. The buffer is huge, but its capacity is certainly not infinite.