Over and over at the UN climate summit in Glasgow, world leaders have stressed the need to limit global warming to 1.5°C.

The 2015 Paris Agreement commits countries to limit the global average temperature rise to well below 2°C above pre-industrial levels, and to aim for 1.5°C.

Scientists have said crossing the 1.5°C threshold risks unleashing far more severe climate change effects on people, wildlife and ecosystems.

Preventing it requires almost halving global CO2 emissions by 2030 from 2010 levels and...