After a moderate start to the year, temperatures have been at record levels since June. This is primarily due to the El Niño climate phenomenon, which has a particularly strong impact on ocean temperatures. Given the current circumstances and further forecasts, it is virtually certain that 2023 will set new standards in the end.
The year to date in figures
At the beginning of the year, we were in weakening but still prevailing La Niña conditions. La Niña is the counterpart to El Niño, both of which are part of ENSO and have a major impact on global temperatures. In short, global average temperatures tend to be lower during La Niña and higher than average during El Niño (more information on this topic can be found here, for example). Despite this sign, January was 0.25 degrees above normal globally (average for the years 1991-2020), making it the seventh warmest in recorded history (in Europe it even ranked third). As the year progressed, there was a gradual transition from La Niña to a neutral phase and, from early summer, to El Niño. This change is very clearly reflected in the global temperature deviations, which have been at an absolute record level since June. A strong El Niño in combination with general global warming therefore leads to the extreme temperature anomalies. In any case, all monthly records at a global level have been set in the last seven years; the last time El Niño was as strong as this year was in 2016.
| Month | Deviation 2023 (vs. 1991-2020) | Place | Record year |
| January | +0.25°C | 7 | 2020 |
| February | +0.29°C | 5 | 2016 |
| March | +0.51°C | 2 | 2016 |
| April | +0.32°C | 4 | 2016 |
| May | +0.40°C | 2 | 2020 |
| June | +0.53°C | 1 | 2019 so far |
| July | +0.72°C | 1 | so far 2019 |
| August | +0.71°C | 1 | so far 2016 |
| September | +0.93°C | 1 | so far 2020 |
| October | +0.85°C | 1 | so far 2019 |
| November | 2020 | ||
| December | 2019 |
On record course since June
Since June, all months have set new records, in some cases by a considerable margin. The months of July to October were particularly impressive, beating the previous record months by between 0.3 and 0.5 degrees – these are not just new records, on a global scale such figures are a completely new dimension! July was also the warmest month in recorded history with an average of 16.95 degrees, with August 2023 taking second place this year with 16.82 degrees. Also astonishing, this year's September was 18th place overall – more than exceptional for a transition month.
Fig. 1: Development of the global surface temperature; Source: Climate Reanalyzer
Very high ocean temperatures
El Niño has a particular impact on the ocean surface temperatures of the equatorial Pacific due to the changed wind patterns. At times, the deviations here amounted to more than 5 degrees. But it is not only the Pacific that was and is partly responsible for the current high surface temperatures; the rest of the oceans are also often at above-average temperatures. We have been in unprecedented territory in this area for a good of eight months now. And an imminent return to an average level is not yet foreseeable. The black highlighted line in the diagram below shows the current year ocean temperatures between 60°S and 60°N. At currently 20.8 degrees, for example, we are 0.2 degrees above the previous record for this time of year (2015) and around 0.8 degrees above the 1982-2011 norm.
Little sea ice, darker surface
The oceans are not only much warmer than usual between 60°S and 60°N, the effects of the higher temperatures are also clearly visible in the polar regions. Here, this is primarily due to the extent of the sea ice. In the Arctic, the sea ice covered an area of 6.9 million square kilometers in October, which corresponds to a deficit of around 12 % (0.9 million square kilometers) (Figure 3). The picture is even more extreme at the opposite pole. Never before has the sea ice deficit in the Antarctic been as large as this October. The deviation is around 2 million square kilometers or 11 % (Figure 4). The previous record dates back to 1986 and was "only" -5 %.
Fig. 3: Sea ice anomaly in the Arctic; Source: Copernicus
Fig. 4: Sea ice anomaly in the Antarctic; Source: Copernicus
Temperatures and sea ice extent go hand in hand. However, there is also a mutually reinforcing feedback mechanism. Less sea ice means more exposed water. As the sea surface is darker than the ice surface, less incoming solar radiation is reflected. More energy is absorbed and thus stored in the Earth system (here primarily in the ocean). This is a cycle that continues to intensify.
Warmest year almost certain
Against this backdrop, it seems almost certain that 2023 will be the warmest year in recorded history. On the one hand, the "lead" over the previous record (2016) is currently around 0.1 degrees and, on the other hand, the months of November and December were rather average in temperature. In the final calculation, the previous record year 2016 shows a deviation of +0.44 degrees compared to 1991-2020. For the current year, however, further above-average conditions are expected for November and December due to the ongoing El Niño conditions, the high surface temperatures and the low sea ice extent. In total, 2023 is expected to show a deviation of between +0.51 and +0.58 degrees according to estimates. We will of course keep you up to date.
Fig. 5: Temperature deviations in recent decades; Source: Copernicus
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