Serendipity

We spent some time in my climate change class this week talking about Hurricane Sandy – it’s a fascinating case study of how climate change alters things in complex ways. Some useful links I collected:

• Here are some spectacular photos of the damage (including one that my students pointed out looks like a scene from the movie Titanic).
• For more on what was unusual about Sandy, see this NCAR article “Four Surprises from Sandy”, and from last weekend, as the storm approach New Jersey, this article in the Atlantic “Why Sandy Has Meteorologists Scared in 4 Images“.
• On CNN, Ben Orlove talks about the connection between Sandy and climate change, and, from the AGU blogs, What Those Who Understand Atmospheric Physics Are Talking About After Sandy.
• For some lessons about our ability to heed the warnings from scientists, see Chris Mooney’s post NASA Warned New York About Hurricane Danger Six Years Ago

In class we looked in detail about the factors that meteorologists look at as a hurricane approaches to forecast likely damage:

• When will it make landfall? If it coincides with a high tide, that’s far worse than it it comes ashore during low tide.
• Where exactly will it come ashore? Infrastructure to the north of the storm takes far more damage than infrastructure to the south, because the winds drive the storm surge in an anti-clockwise direction. For Sandy, New York was north of the landfall.
• What about astronomical conditions? There was a full moon on Monday, which means extra high tides because of the alignment of the moon, earth and sun. That adds inches to the storm surge.

All these factors, combined with the rising sea levels, affected the amount of damage from Sandy. I already wrote about the non-linearity of hurricane damage back in December. After hurricane Sandy, I started thinking about another kind of non-linearity, this time in the impacts of sea level rise. We know that as the ocean warms it expands, and as glaciers around the world melt, the water ends up in the ocean. And sea level sea level rise is usually expressed in measures like: “From 1993 to 2009, the mean rate of SLR amounts to 3.3 ± 0.4 mm/year“. Such measures conjure up images of the sea slowly creeping up the beach, giving us plenty of time to move out of the way. But that’s not how it happens.

We’re used to the idea that an earthquake is a sudden release of the pressure that slowly builds up over a long period of time. Maybe that’s a good metaphor for sea level rise too – it is non-linear in the same way. What really matters about sea level rise isn’t its effects on average low and high tides. What matters is its effect on the height of storm surges. For example, the extra foot added to sea level in New York over the last century was enough to make the difference between the storm surge from Hurricane Sandy staying below the sea walls or washing into the subway tunnels. If you keep adding to sea level rise year after year, what you should expect is, sooner or later, a tipping point where a storm that you could survive previously suddenly become disastrous. Of course, it doesn’t help that Sandy was supersized by warmer oceans, fed by the extra moisture in a warmer atmosphere, and pushed in directions that it wouldn’t normally go by unusual weather conditions over Greenland. But still, it was the exact height of the storm surge that made all the difference, when you look at the bulk of the damage.