Weatherwatch: warmer water drives higher-than-expected rise in sea level

Nasa data for 2024 shows reversal of dynamic in which melting ice usually accounts for majority of increase

Normally, two-thirds of sea level rise is due to melting ice from mountain glaciers and Greenland and Antarctic ice caps, and one-third from the thermal expansion of the oceans.

Last year, the hottest year on record, this was reversed, with warmer water accounting for two-thirds of the sea level rise of 0.59cm (0.23in) – considerably more than the 0.43cm scientists were expecting. Nasa, the US agency that produces the figures from its satellite data, believes that the mixing of hotter surface waters with cooler sea at depth during an El Niño year may have caused this unexpected blip, although more violent winds could also have been a contributing factor.

Sea level rise between 1993, when satellite measurements began, and 2024 is 10.1cm and accelerating, and is expected to reach 17.78cm by 2040 – although as the climate continues to warm, this may be an underestimate.

Nasa, being an American institution, worries about large parts of Florida going under as a result of storm surges, but Mediterranean cities are already suffering. The worst-affected is Alexandria in Egypt, where 280 buildings have collapsed in 20 years because of sea level rise and coastal erosion. With many parts of Europe’s coast, especially around the North Sea, already at or below sea level, some destruction is inevitable.

Cover photo:  A beach in the Egyptian city of Alexandria, where sea level rise and coastal erosion have caused the collapse of 280 buildings over the past 20 years. Photograph: Mohamed Abd El Ghany/Reuters