WHEN an army confronts a heavily defended enemy, it has two options a full-frontal attack or a siege. In the battle against climate change and its cause, there is a similar choice.

The all-out attacks are mega-schemes to convert the Sahara into a giant solar energy farm, or supergrids connecting renewable energy plants across continents. These are dazzling, flashy proposals. Global geo-engineering plans are even more pulse-quickening, aimed as they are at changing the reflectivity of the entire planet.

Yet such spectacular attacks are high-risk, easily turning into crashing, expensive failures. Sieges are the wise general`s choice. And in the context of carbon dioxide emissions, the siege strategy equates to energy efficiency. That means switching stuff off, or building it to use less energy in the first place.

A report last year from the consulting group McKinsey found that even implementing only those energy efficiency measures that pay for themselves at sensible rates of return could reduce the energy needed in 2020 by about a quarter. That would be halfway towards the emissions cuts that give a decent chance of limiting global warming to under 2C. A more homely example if everyone in the UK bought the most efficient fridges, freezers and washing machines, the carbon saving would equal taking around 1.4m cars off the road.

From a policy perspective, the remedy is clear minimum energy efficiency standards.

— The Guardian, London