Record temperatures in the Mediterranean.1 Huge heat wave in the North Atlantic.2 The temperature of the oceans at an all-time high.3 The ocean’s fever chart has been covered in the media since early summer. While this was probably the first time many people in Switzerland had heard of marine heat waves, these reports came as little surprise to me.
As climate scientists, we understand very well how human-induced global warming is also pushing up ocean temperatures. The ocean is the primary thermal buffer in the Earth’s climate system, absorbing more than 90 percent of the additional heat resulting from greenhouse gases such as CO2. So, in and of itself, it’s not surprising that marine heat waves are becoming more frequent and intense.4 But I have to admit that I wasn’t prepared for what’s currently happening in the oceans: the intensity and magnitude of the heat waves is enormous, and the rapidity of the warming fills me with concern.
In uncharted territory
In recent weeks, the global average temperature of the sea surface has reached 21.1 degrees Celsius – the highest ever recorded. That’s 0.3 degrees warmer than the previous record temperature at this time of year. Since the spring, the temperature curve for 2023 has been about 1 degree above the 1982–2011 average.