ADAM SOBEL, Columbia University:

Well, I think you have to talk about each event separately.

So let's start with the Louisiana event. I think the California situation is a little bit different and has been going on for a number of years. So, there have actually been a few studies specifically on that event.

But since we're talking about Louisiana and the floods now, just for some general context, I mean, across the United States, as well as most places in the world where there is adequate data to ask the question, we have seen increases over the last decades, or in some cases the last century, in the extremity of severe rain events.

So, we see heavy rain events becoming heavier and a larger fraction of the rain falling at heavy events. And this is what our climate projections tell us should happen as the climate warms, although to uncertain degrees, but it's qualitatively consistent. And we expect it on physical grounds, as a warming climate means that there is more water vapor in the atmosphere.

Now, it's true that each individual event is a result of many factors, and climate change is at most one of them, and usually a small one. So a lot of things have to happen for an extreme event to occur. Otherwise, it wouldn't be an extreme event. And so climate change can at most push the odds a little bit in one direction.

So, I mean, we now have a new emerging area of science called extreme event attribution, where people actually do studies and have ways of making probabilistic statements. You can't ever say this event was caused by climate change or this single event is conclusive evidence of climate change.

But you can say that climate change appears to have made it such a percent more probable, or given that it occurred, make it such and such percent more extreme.

Those studies haven't yet been done on the Louisiana event. My guess is that they will be done pretty soon. They can get done pretty quickly now. And I would cautiously predict that they are going to show some increase in the likelihood of this happening due to climate change, although I wouldn't want to put a number on it.

So, that is the sort of broad context. I think it is the kind of thing we expect to see more as the future proceeds. And it's the kind of thing we have been seeing. But I agree that to make stronger statements than that about a specific event, it is certainly possible to overstate the connection. But there is a lot of science behind the statement that there may be some connection there.