Let’s try this again: It is nonsense to say that we don’t know whether a specific weather event was affected by climate change. It’s not just wrong, it’s nonsensical.

This post is by Phil Price, not Andrew.

If you write something and a substantial number of well-intentioned readers misses your point, the problem is yours. Too many people misunderstood what I was sayinga few days ago in the post “There is no way to prove that [an extreme weather event] either was, or was not, affected by global warming” and that’s my fault.  Let me see if I can do better.

Forget about climate and weather for a moment. I want to talk about bike riding.

You go for a ride with a friend. You come to a steep, winding climb and you ride up side by side. You are at the right side of the road, with your friend to your left, so when you come to a hairpin turn to the right you have a much steeper (but shorter) path than your friend for a few dozen feet. Later you come to a hairpin to the left, but the situation isn’t quite reversed because you are both still in the right lane so your friend isn’t way over where the hairpin is sharpest and the slope is steepest. You ride to the top of the hill and get to a flat section where you are riding side-by-side.  There is some very minor way in which you can be said to have experienced a ‘different’ climb, because even though you were right next to each other you experienced different slopes at different times, and rode slightly different speeds in order to stay next to each other as the road curved, and in fact you didn’t even end up at exactly the same place because your friend is a few feet from you.  You haven’t done literally the same climb, in the sense that a man can’t literally step twice in the same river (because at the time of the second step the river is not exactly the same, and neither is the man) but if someone said ‘how was your climb affected by your decision to ride on the right side of the lane rather than the middle of the lane’ we would all know what you mean; no reasonable person would say ‘if I had done the climb in the middle rather than the right it would have been a totally different climb.’

You continue your ride together and discuss what route to take where the road splits ahead. One road will take you to a series of hills to the north, the other will take you to a series of hills to the south. You decide to go south. You ride over some hills, along some flat stretches, and over more hills. Three hours into the ride you are climbing another hill, the toughest one yet — long, with some very steep stretches and lots of hairpin turns. As you approach the top, your riding companion says “how would this climb have been different if we had gone north instead of south?”  What is the right answer to this question? Here are some possibilities: (1) “There is no way to prove that this climb either was, or was not, affected by our decision to go south instead of north.” (2) “The question doesn’t make sense: we wouldn’t have encountered this climb at all if we had decided to go north.” (3) “This climb was definitely affected by our decision to go south instead of north, but unless we knew exactly what route we would have taken to the north we can’t know exactly how it was affected.”

1 is just wrong (*).  If you had gone north instead of south you might still had a steep climb  around hour 3, maybe it would have even been a steeper climb the one you are on now, but there is no way it could have been the same climb…and the difference is not a trivial one like the “twice in the same river” example.

2 is the right answer.

3 is not the right answer to the question that was asked, but maybe it’s the right answer to what the questioner had in mind. Maybe when they said “how would this climb have been different” they really meant something like, if you had gone the other way, “what would the biggest climb have been like”, or “what sort of hill would be climbing just about now”?

I think you see where I’m going with this (since I doubt you really forgot all about climate and weather like I asked you to).  On a bike ride you are on a path through physical space, but suppose we were talking about paths through parameter space instead. In this parameterization, long steep climbs correspond to hurricane conditions, and going south instead of north corresponds to experiencing a world with global warming instead of one without. In the global warming world, we don’t experience ‘the same’ weather events that we would have otherwise, but in a slightly different way — like climbing the same hill in the middle of the lane rather than at the side of the lane — we experience entirely different weather events — like climbing different hills.

The specific quote that I cited in my previous post was about Hurricane Katrina. It makes no sense to say we don’t know whether Hurricane Katrina was affected by global warming, just as it would make no sense to say we don’t know whether our hill climb was affected by our decision to go south instead of north. In the counterfactual world New Orleans might have still experienced a hurricane, maybe even on the same day, but it would not have been the same hurricane, just as we might encounter a hill climb on our bike trip at around the three-hour mark whether we went south or north, but it would not have been the same climb.

No analogy is perfect, so please don’t focus on ways in which the analogy isn’t ‘right’. The point is that we are long past the point where global warming is a ‘butterfly effect’ and we can reasonably talk about how individual weather events are affected by it. We aren’t riding up the same road but in a slightly different place, we are in a different part of the territory.

(*) I’m aware that if you had ridden north instead of south you could have circled back and climbed this same climb. Also, it’s possible in principle that some billionaire could have paid to duplicate ‘the same’ climb somewhere to the north — grade the side of a mountain to make this possible, shape the land and the road to duplicate the southern climb, etc.  But get real. And although these are possible for a bike ride, at least in principle, they are not possible for the parameter space of weather and climate that is the real subject of this post.

This post is by Phil, not Andrew.