Part 3 (Katrina-specific): Legal theories of causation, hurricanes, and climate change

Part 1 of this series found that climate change easily satisfies the first required part of causation under the law, being a "but-for" cause of hurricanes. Part 2 found that the second required part, "proximate cause," couldn't be proven for the mere fact that a hurricane existed and injured someone, but probably could be found as a general matter for some as-yet undefined increase in hurricane intensity.

But can a court find that proximate cause exists for the increase in intensity of a specific hurricane, say Hurricane Katrina? This question is complicated, I think, because the but-for cause (multiple influences on chaotic weather systems) and proximate cause (increase in sea-surface temperatures) derived from global warming are different. Usually the law analyzes the same alleged mechanism to see if it satisfies both but-for and proximate cause. Remember, absent global warming, Hurricane Katrina would not have existed. It's difficult to ask how much of Katrina's damage is especially attributable when all of the hurricane's damages are attributable to warming, but not necessarily especially attributable.

Here's the closest I can get to an answer, using another thought experiment. Suppose it's late August 2005, and just as Hurricane Katrina crosses west over Florida, some technologically-advanced space aliens decide to conduct an experiment. Using means we don't understand, they remove all effects of anthropogenic global warming from sea-surface temperatures in the Gulf of Mexico. (I'm simplifying things to assume at this point in time, no other AGW-effects will do much to Katrina). This seems like a strange thought experiment, but it's the only way I can examine the issue. So what happens in this thought experiment?

If climatologists could say, "under this scenario, we're certain that the Gulf's sea surface temperatures in August-September 2005 would decrease," and given how the otherwise-unchanged conditions otherwise allowed Katrina to maximize intensity, then we could say it's likely that AGW-caused temperature increase made Katrina still more intense, and proximate cause has been satisfied. I doubt climatologists could deliver this certainty, though. Instead they'll say there's a range of probability that the Gulf was artificially-warmed. I doubt that probability, reduced by the large-but-not-100% probability that the sea temperature warming would also have the effect of intensifying Katrina, would be enough to show proximate cause.

This isn't the end of the story, though. Climatologists will be getting more certain about the specific, regional effects of climate change. And if you broaden your potential lawsuit from my single example of a newborn baby to a whole class of widely-distributed hurricane victims, then proximate cause becomes a lot easier to demonstrate. Similarly, showing proximate cause for increased insurance costs or inability to get insurance is also easier. Litigation on this type of issue is increasingly viable.

UPDATE: Welcome, readers from ExxonMobil's Internet Service Provider! That's an interesting blog search you've got going. Seriously, I am glad if oil companies are taking private litigation issues seriously. Oh, and please stop funding the inanity at the American Enterprise Institute.