It was interesting to write – not just to clarify a few details for myself, but also to realise quite how hard it is to source reliable information on this stuff. Even the IPCC reports don’t make it crystal clear whether they’re talking about concentrations of greenhouse gases or greenhouse gases minus aerosol cooling. And lay-friendly writes up regularly confuse CO2 with CO2e, fudge baselines for emissions cuts, and so on.
Anyway, thanks to the Met Office for fact checking it – and if anyone finds it useful, feel free to repurpose it. Like most of the FAQ answers, it’s released under a Creative Commons license.