The idea of net zero was brought into mainstream thinking following the Paris Agreement in 2015, but the idea was developed in the IPCC Fifth Assessment Report in 2013 which stated that limiting global temperature change means limiting the cumulative CO2 emissions in the atmosphere – and this, in order to eventually stop global warming, net anthropogenic additions of CO2 into the atmosphere would have to reach zero.
The Paris Agreement (section 4.1) stipulated that
"In order to achieve the long-term temperature goal set out in Article 2, Parties aim to reach global peaking of greenhouse gas emissions as soon as possible, recognizing that peaking will take longer for developing country Parties, and to undertake rapid reductions thereafter in accordance with best available science, so as to achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century, on the basis of equity, and in the context of sustainable development and efforts to eradicate poverty."
This is the key net zero text.
The meeting [it was COP21] although widely regarded as insufficiently ambitious, was crucial for this statement. In addition, it established new global responsibilities, expectations and mechanisms, imperfect that they, inevitably are. And it gave rise to the need for countries to talk to each other reasonably seriously through subsequent COPs. Sweden was the first country to put a mid-century (by 2045) net zero target into law, followed by the UK (by 2050). Currently 101 countries have a net zero goal although the extent of legal enshrinement varies considerably. There's a short history of net zero c/o the Energy and Climate Change Intelligence Unit.
How "in the second half of this century" became "by 2050" is not clear. An increased sense of urgency, perhaps? Macho politicians, maybe, anxious to be seen to be on the right side of history, as if history cared. But then there's something about dates ending in 0 and the mid-century 50 offered a prominent bulls-eye to aim at.
Importantly, net zero does not mean zero. What the idea does is to make clear that there will be a need to balance residual greenhouse gas production with sinks to absorb the excess.
There is at least one UK educational NGO, Let's Go Zero, that talks about zero rather than net zero. When I queried this with them, they said they do this because they think that people don't understand 'net'. An ideal opportunity to explain it, I thought. Other groups simply want there to be zero carbon asap despite the social and economic disruption that would ensue. They have been gifted a lot of unchallenged air time of late.
History is never finished as we know, and we continue to write the net zero chapter with a particularly intense drafting workshop going on in Dubai which may need new sustainability literacy skills to be developed.
I think that the goal of net zero is the most challenging of tasks humanity has ever faced. It's not just existential it's truly global with no escape from it no matter how rich or well connected you are. It's a problem we'd rather not have, I guess, but, as we have it it is surely going to need to bring out the best in us if we are to succeed. That's a meliorist statement of hope tinged with a bit of optimism. This is going to sound rather hubristic, but I'm glad to play a vanishingly small part in this struggle.