Thread by @chrisd_jones

Is there “warming in the pipeline”? maybe surprisingly, no – many expect that our past emissions commit the world to continue warming, but that’s not the case. If we stop emitting (CO2), we will stop warming. Give or take small error bars. Here’s why…
bg.copernicus.org/articles/17/29…

For a while (e.g. science.org/doi/epdf/10.11…), there was a lot of attention on how climate may continue to warm if we stabilise CO2 levels. So-called “committed warming”, or “warming in the pipeline”. The science isn’t changed, but there is a realisation this isn't the best question

Why would we want to stabilise CO2 levels? We would have to keep emitting CO2 to keep CO2 constant. Better, therefore, to stop emitting and let CO2 reduce. The natural land and ocean carbon sinks will continue to operate

All models agree that CO2 comes down pretty rapidly if emissions stop – in these experiments it’s a sudden stop (to let us explore the behaviour of the system). Obviously in reality it needs to be more phased – but still urgent and rapid.

The reducing radiative forcing as CO2 drops balances any un-realised warming past levels. The result is that global temperature approximately stays constant – so now we can talk about climate stabilisation rather than CO2 stabilisation (known as the “Zero Emissions Commitment”)

Of course, other things don’t stop straight away. Ongoing sea-level rise is unavoidable – but we _can_ reduce the speed and extent of it happening.

But this good news – we can stop warming if we stop emitting – is what lets us set a carbon budget. To stay within a temperature goal we can quantify how much CO2 we can emit before we reach it. For 1.5 it’s almost all gone, but 2 degrees it’s still possible with renewed efforts