September broke heat records everywhere

Record atmospheric and oceanic temperatures are forcing scientists to reach for explanations beyond greenhouse gases and the periodic Pacific warming known as El Niño. This does not mean they are discounting the effects of CO2 and methane emissions. Far from it. These remain by far the most significant factors behind global average surface temperatures last month that were 0.5 degrees C higher than for any previous September and 0.93 degrees higher than the September average for 1991-2020 (which is itself about a degree higher than the average for the previous half-century). Zeke Hausfather of the Berkeley Earth climate data project called the numbers “gobsmackingly bananas”. US data also show 2023 North Atlantic surface temperatures to be about a degree above their previous record and more than 2 degrees above their rolling average. El Niño is a factor – and could paradoxically deliver record storms in the western US this winter – but others may include the 11-year solar cycle, falling sulphur emissions from shipping and heat-trapping water vapour from a submarine volcanic eruption off Tonga last year.