We passed the 1.5C climate threshhold. We must now explore extreme options | Sir David King

Last year marked a historic and deeply troubling threshold: for the first time, global temperatures exceeded 1.5C above pre-industrial levels.

The consequences rising sea levels, extreme weather and devastating loss of biodiversity are no longer projections for the distant future.

Scientists agree we need to bring greenhouse gas levels down to below 350 parts per million by the end of this century .