As @SimonLLewis points out, lots of net zero discussions this week questioning its value as a target (and in some cases implying that it is a barrier to action and actively unhelpful). I think the UK experience in setting the target provides some insights – short 🧵... https://twitter.com/SimonLLewis/status/1386962287844593666
UK story on this starts in 2008, when the Climate Change Act set a target of 80% emissions reduction by 2050 - extremely ambitious at the time. That target was around long enough to become part of the furniture, and was rarely questioned. Net zero not really on the radar.
Next big milestone was 2015, when the Paris Agreement committed to net zero “in the second half of the century”. Fairly innocuous wording, but a really important hook for campaigners (who also deserve credit for introducing the concept).
Fast forward to 2017 – net zero was not even mentioned in any party manifesto at the election in May of that year. In October of that year the Clean Growth Strategy said virtually nothing on net zero – just the para below. Very much not a commitment to legislate any time soon.
Then in early 2018, @PlanB_earth legal action against the UK’s 2050 target (of 80% at the time) gathered pace. The government announced in April of that year that it would be reviewing the target. Perhaps coincidence, perhaps not… https://planb.earth/plan-b-v-uk/ 
HMG responded remarkably quickly – legislating within just a few weeks. This happened just as Theresa May was leaving office; again, perhaps coincidence, perhaps not…

By the 2019 election, every major party included a commitment to net zero in their manifesto.
Was this in order to avoid short-term action? That wasn't my experience. Since setting net zero, the UK has increased other targets – to 68% against 1990 levels by 2030 (from 57%), and 78% by 2035 (i.e. bringing forward the old 80% target by 15 years). https://twitter.com/timbolord/status/1374421629334290435
And it’s increased the scale of action e.g. through the Ten Point Plan, and increased HMG focus through new Cabinet Committees. Still much more to do - net zero didn't solve the problem of short-term action, but it did accelerate progress.
Experience in the UK shows the importance of campaigning / grassroots in developing the concept; strong legal framework on climate; independent advice from the CCC; luck in political timing. And that NZ can galvanise step-change in action, even if there's more to do. [/ends]
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