Do we have any low-risk global geoengineering options ready to deploy now? The answer, according to leading US climatologist Alan Robock, is no. So it is unsurprising that interest is starting to turn to more limited, localised ideas that look less perilous.

The latest involve building artificial islands and 100-metre-high walls to prevent a rising tide of melting polar ice. These examples of targeted geoengineering – a new twist on the controversial idea – could prevent the metre or so of sea level rise that is expected …