On Sandy and climate change

On Sandy and climate change

As seawater floods into lower Manhattan, seeping into subway stops and tunnels, many are talking up the link between climate change and severe storms.

But this is a tricky link to make. As Brad Plumer notes over at WonkBlog, "trying to attribute specific hurricanes to changes in global temperature remains quite difficult." He adds: "In its big report on natural disasters last year, the Intergovernmental Panel on Climate Change (IPCC) said it had “low confidence” that humans were currently affecting tropical cyclone patterns. Hurricanes are far more complicated to study than, say, heat waves and the historical record is patchier."

I emailed MIT’s Kerry Emanuel, one of the foremost experts on hurricanes, what he makes of this:

I am not sure we scientists understand the link all that well. North Atlantic hurricane power has been tracking tropical Atlantic sea surface temperature for over a century of record, and we think the recent increase in Atlantic SST (and hurricane power) is related both to increasing greenhouse gases and decreasing sulfate aerosol pollution, both man-made trends.

Sandy is an example of a hybrid storm, drawing energy both from the evaporation of seawater, the source of energy for tropical hurricanes, and from horizontal temperature contrasts, the source of energy for winter storms. But we have not done a comprehensive climatology of hybrid storms, so we do not know whether there are trends in their incidence, nor have we studied how they change in climate model simulations. Thus we really have no basis for saying anything useful about their relationship to climate.

Increased incidence of drought and floods are well predicted consequences of greenhouse gas-induced warming. But we know little about the relationship between climate and  severe thunderstorms and their attendant tornadoes and hailstorms. We have a long way to go, alas.

But even if storms are only marginally more intense or frequent, they can still do a lot more damage as our cities gets denser. As John Seo, a hedge fund manager who specializes in catastrophe bonds — financial instruments used to hedge against the risk of low-probability events — warns, "a decade and a half from now, a single hurricane or earthquake will come with a potential price tag of $1 trillion or more."

What’s more, even if the link between such storms and climate change were more solid, anything we could have done in recent years to reduce greenhouse emissions wouldn’t have mattered as far as Sandy is concerned — at this point, we’re talking about trying to limit ill effects decades from now. As Grist‘s Dave Roberts puts it, "The oceans will continue to rise for at least 50 years no matter what we do. We can only affect the latter half of century."

Have a nice evening.