Friday, 2 November 2012

"This Is What Climate Change Looks Like"

Even as America's East Coast continues to recover from the impact of Hurricane/"Superstorm" Sandy, pundits are using it as a teachable moment to talk about climate change. Perhaps the most in-your-face comment along these lines appeared on the cover of Businessweek:

My preference for precision makes me wince a little when I see statements like this.  As I noted in an earlier post, there is a difference between weather and climate. A hurricane - even one as big and destructive as Sandy - is weather.  Weather is what you see when you look out the window on any particular day. Is it sunny? Is it snowing? Are there 70 mph winds and driving rain?  That's weather.

"Climate" is a description of the conditions you can reasonably expect given the location and time of year.  If it's autumn on the U.S. East Coast, you can reasonably expect a handful of hurricanes to strike.  Warmer ocean temperatures provide even more energy to power hurricanes, and we know that the planet is warming as a result of fossil fuel use, deforestation and other practices. As a result of global warming, then, we expect a changing climate with more and stronger hurricanes. But it's very challenging to point to any one storm and say, "Aha! Climate change made that happen!"

Meteorologists believe that increased freshwater as a result of Arctic melting may have contributed to the cold front that steered Sandy onshore. Those who are looking for a teachable moment are saying that all of this proves we are suffering from climate change impacts.  But as with hurricanes in autumn, cold fronts are not unknown in the north Atlantic.  It's an amazing coincidence, and matches very closely what we would expect in a warming world.  But again, if we want to be as accurate as possible, when describing any particular incident we are talking about weather. Our models are not sufficiently fine-grained to allow us to draw the causal link more directly than that.  At least not yet.

The danger with definitively attributing a bad weather event to climate change is that it can cut both ways.  When campaigners claim that a warm, snow-free winter is evidence of climate change, climate deniers can claim that a cold snap and blizzard the following year make the opposite case. Trends and statistics allow a more nuanced debate.

Businessweek quotes Eric Pooley of the Environmental Defense Fund, who uses a sports analogy: “We can’t say that steroids caused any one home run by Barry Bonds, but steroids sure helped him hit more and hit them farther. Now we have weather on steroids.” Steroids and other performance enhancing drugs increase the likelihood that a world class athlete will win games and break records, just as climate change increases the likelihood that we will experience monster hurricanes and other impacts.

This does not mean we can't use Sandy to have a serious conversation about global warming.  Rather than saying, "This is climate change," I might say, "This is what climate change looks like. We'll have to get used to much more of this if we don't drastically cut emissions."

We don't need 100% certainty before we take action.  People who live in relatively dangerous neighborhoods tend to have more locks on their doors than those who live on safer streets, even though the probability of a robbery is far below 100%.  The insurance industry in particular is very sensitive to the probability of a claim, and uses this information to decide who to insure and what premium to charge.  Even a slightly increased probability of devastating storms, droughts, floods, and the like is enough to spur insurers to change their policies.  When it comes to climate change, insurers are the canary in the coal mine.  They don't need to know that a particular storm or drought is due to climate change, just that those impacts match what we would expect in a warming world.

While I won't yet go as far as that Businessweek headline, I do think Sandy helps sound the alarm.

"This is what climate change looks like."