Puzzle No. 767– Tuesday 22 June Set by CPDN's Professor Myles Allen)

If global warming has reached 1.1°C, warming at 0.2°C per decade, and every tonne of carbon dioxide we emit drives up global temperatures, permanently, by the same amount as every other tonne, how long do we have to reduce global carbon dioxide emissions to net zero to limit global warming to 1.5°C if we start now and reduce at a constant rate?

(Professor Myles Allen may well have answered this when he was the guest on, "The Life Scientific.(Also BBC Radio4))