Cities at sea level around the world – including Bangkok, New Orleans, Shanghai and Amsterdam – are bracing themselves for rising seas and sinking ground. Populations on river deltas, atolls and islands face flooding and displacement. Sea-level rise accumulates slowly, measured in millimetres a year, but the incremental pace can deceive us. Sea-level rise, particularly when combined with sinking land, presents a growing problem.

Consider that the rate of sea-level rise is itself rising. Sea rise remained virtually zero over the last several millennia. Then, in the 20th century, the sea rose about 20 centimeters. Now, today, the rate has reached about 30 centimeters per century, and still increasing. Recently, oceanographers have boosted their predictions of 21st century sea level rise from about 20 centimetres to a metre or more.

Sea-level rise is not uniform around the world. Gravitational forces, including the gravity of ice caps themselves, cause uneven fluctuations. Meanwhile, some coastal plains sink as others rise, so exaggerating sea-level rise in some regions and cancelling it in others. Furthermore, if humanity cannot change its hydrocarbon habits quickly enough, we risk runaway warming that could accelerate sea-level rise.

In an extreme runaway scenario, a complete melting of the Greenland ice sheet would […]