Extreme event attribution is quantitative science fiction. It asks and often answers the question, what if things had been otherwise? What if we’d left all that oil and coal and gas in the ground, felled no trees, made no cement? What if we’d somehow found a route to the present world without all that and without causing any other major upsets to the planet’s radiative balance0. It then focuses on an “event” – a heatwave, downpour, drought, flood, whatever – and overlays these two different worlds – ours and that of our imagination – to see in which one the event was more likely.
This isn’t the only way we could frame the question of course. Science fiction abounds with parallel universes and there are many other worlds we can reach by a small imaginative effort and simulate on our1 super computers. We could ask, are there turning points in history – the first IPCC report, for example – where things might have gone differently? How different would the world have been if the world had taken action then? Alternatively, what if the world had never taken any action at all? What if we had continued burning coal and oil and gas with out the slightest concern for the climate?
Such musings were prompted by the IPCC synthesis report’s garden of forking paths figure (below in modified form). They indicate what could happen in the future, and what might have happened if we hadn’t missed certain opportunities, but they don’t have an equivalent for how bad it might have been if nothing had been done. I’ve added a line and labelled it “disasters averted” which is rather dramatic phrasing, but hopefully you get the idea. I’ve also added the counterfactual “natural” world in which no emissions were emitted at all. I’ve called it “it was all a bad dream”.
When thinking about what climate change means and will mean, I think it’s interesting to compare (at least at this hypothetical level) the differences between all of these counterfactuals at the point marked “Present world”. No amount of plausible climate action will return us to the natural world2, but it is an indicator of how far things have changed. The “opportunities missed” line is interesting, particularly for those inclined to say I told you so, but is also important because it represents what might have been done once we knew the dangers. The “disasters averted” line is interesting because it helps to track how bad things could have been if we hadn’t acted. It tells us, in a sense, what that action has bought us.
0 A world in which no greenhouse gases or aerosols have been emitted, but somehow manages to be like the present world in every other way, is a tricky one to picture.
1 I say “our”, but it’s not like they’re left in public places for just anyone to run their counterfactuals on.
2 I do wonder to what extent the standard framing of event attribution leaves people with the impression that climate action will somehow take us back to the pre-industrial state.