It may be only a matter of time. In its 2007 report, the IPCC projects that sea level will rise anywhere from 180mm to 590mm by 2090–2100. This range is smaller than in the IPCC’s 2001 report, but it excludes some key uncertainties about how quickly warming will melt land-based ice. The last few years have seen glaciers accelerating their seaward flow in many spots along the margins of Greenland and West Antarctica. Computer models don’t depict the dynamics behind this speed-up very well, so it’s not explicitly included in the IPCC projection, but the report does note the added risk at hand. After considering new data on such melting, the US National Research Council estimated in 2010 that sea-level rise from all sources may total 500–1000mm (20–40in) by 2100, though a report in 2011 suggested that the Greenland ice sheet may be safer than previously thought).

However big the rise turns out to be by 2100, sea level won’t stop rising then, which means coastal areas will have to contend with an ever-worsening threat. If emissions continue to rise unabated through this century, the Greenland and/or West Antarctica ice sheets could be thrown into an unstoppable melting cycle that would raise sea level by more than seven metres each. This process would take some time to unfold – probably a few centuries, although nobody can pin it down at this point – but should it come to pass, many of the world’s most beloved and historic cities would be hard-pressed to survive.

This is an edited extract from The Rough Guide to Climate Change by Robert Henson.