Climate change is one of the defining challenges of our time: rising temperatures, linked to greenhouse gas emissions, are causing a range of negative impacts on our planet. One of the most worrying is the rise in sea and ocean levels.

The problem could be even more urgent than previously thought, according to a new study conducted by researchers at Harvard University and published in the journal Nature. Over the past two decades, sea levels have risen more rapidly than expected and are threatening coastlines from Florida to Bangladesh.

The study analysed tidal data collected from around the world between 1901 and 1990 and concluded that the acceleration has been greater than previously assumed, with earlier observations found to be incomplete or skewed. "The new analysis shows that over the past twenty years sea levels have risen 25 per cent faster than previously thought," said Carling Hay, a Harvard researcher and lead author of the study.

The rise in sea levels, caused by the melting of glaciers, had an annual average of 1.2 millimetres between 1901 and 1990, whereas over the past two decades it has increased to reach 3 millimetres per year. "The new findings confirm that sea level is rising, and at rates faster than have ever been recorded," said Stefan Rahmstorf, an oceanographer at the Potsdam Institute for Climate Impact Research.

Rising waters affect everyone, but the first to bear the consequences would clearly be countries with coastlines on seas and oceans. Coastlines from Miami to Shanghai are already being gnawed away by the slow but inexorable advance of the water. Entire islands and atolls in tropical seas risk disappearing, and coral reefs — among the most precious ecosystems on the planet — would suffer irreparable damage.