The average global temperature fluctuates between 13 and 17 degrees during the course of a year. The highest values are typically reached at the end of July. There are various factors that influence temperatures in the short and long term. These include, above all, the interplay between El Niño and La Niña. However, this factor is not sufficient to explain the current record high average temperatures.
La Niña is history – Transition to El Niño
Over the course of the spring, it has become apparent that the unusually long La Niña phase will come to an end this year. In recent weeks, this prediction has also been confirmed by the observed ocean temperatures on the Pacific East Coast. We have long been in a neutral phase between La Niña and El Niño. The latter will become established as the year progresses. More information on the El Niño Southern Oscillation (ENSO) is available in this blog, and possible implications for this year's Atlantic hurricane season are summarized here.
Typically, average global temperatures go down somewhat during a La Niña phase, and up during El Niño years. This is due to the warmer surface temperatures of the central equatorial Pacific. From this context and with the fact that we are currently in a transition phase from La Niña to El Niño, increasing average temperatures on a global scale can therefore be expected - this is exactly what we are currently observing. Interestingly, the current global average temperature is now already at an absolute record level for the time of year in advance of the emerging El Niño. At about 16.6 degrees on average, the excess compared to the 1979 to 2000 average is about 0.7 degrees. Doesn't sound like much, but on a global scale it's extreme and about 0.2 degrees above the previous record in 2019 (at this point in the year). Incidentally, the annual variation in temperatures can be explained by the uneven distribution of land and water masses in the two hemispheres. Land areas warm faster than water areas. Since the northern hemisphere has a larger proportion of land mass than its southern counterpart, global temperatures therefore reach their highest values in the northern summer.
Fig. 1: Global average temperature in long-term comparison; Source: Climate Reanalyzer
The current phase of ENSO only partially explains these temperatures. That's because a recent study found that the positive deviation in surface temperature per degree Celsius in a particular region in the Pacific Ocean, called Niño 3.4 (5°N-5°S, 120°W-170°W), causes global temperatures to be about 0.07 degrees higher. Currently, the Niño 3.4 index is a scant degree above normal, so global temperature would only be directly affected in the low decimal range.
Generally warm oceans
So, in addition to ENSO, other factors must be contributing to this high global temperature. On the one hand, global temperature, like any other meteorological and climatological variable, is subject to natural and temporal variation . It means that a multitude of regional and supra-regional processes are interlinked and cause the temperature to rise or fall for short periods of time. This "noise" can be seen well in the jagged progression of the temperature curves above. Since in the current case the temperature is far from the norm, however, even these explanations are no longer sufficient.
Here the general surface temperature of the oceans comes into play. It is not only the equatorial Pacific that is currently warmer than average, but also large parts of the rest of the world's oceans show a similar picture. This can be seen particularly impressively in the North Atlantic. Regionally, water temperatures are about 4 degrees above normal, while the average surface temperature is 22.7 degrees, about 1 degree above average.
Fig. 2: Variations in North Atlantic surface temperatures compared with the 1971-2000 average.; Source: Climate Reanalyzer
Globally, the picture is not much different. Temperatures in the world's oceans between 60°S and 60°N have been moving into new spheres for months now, and are about 2 tenths of a degree above last year's record. On average, the surface water is about half a degree warmer than normal.
Fig. 3: Sea surface temperature between 60°S and 60°N; Source: Climate Reanalyzer
Recent records
In the wake of high temperatures, it is not surprising that impressive records have been set in recent days. For example, an extremely high 33.4 degrees was measured yesterday in Mexico at an altitude of about 2600 meters (La Bufa), one of the highest values ever at this altitude level. On Sunday, 49.3 degrees was recorded in Sanbao, China, not only setting a new national record for the month of June, but also equaling the second-highest temperature on a global scale in 2023 (the previous leader is Turbat, Pakistan, where 49.5 degrees was recorded on June 7). Senegal also set a June national record of 48.0 degrees (Matam), and parts of Siberia (e.g., Klyuchi) broke the 40-degree mark earlier this month.
We will probably see more records fall in the near future. Some researchers are already predicting a new record year for 2024, when the full effect of El Niño should kick in.
