India, Sept. 3 -- The UN Environment Programme said on Wednesday that global temperature rise will, now inevitably, cross 1.5degC within a few years, and that even the most optimistic pathway it modelled peaks at 1.8degC above pre-industrial levels. Most other pathways peak higher. The overshoot can still be held short and then reversed, the report argues, and that possibility needs to be taken seriously to stave off unseen catastrophes.

The report is also candid about what comes now: Adaptation has limits, and irreversible losses and permanently changed conditions are certain. Risks intensify with every additional fraction of a degree and every year spent above the threshold, some impacts accumulate and others arrive abruptly, and the t...