UPDATE: Turns out it was legitimate to ask weather the temperature played a role — the feds did examine this issue in detail, but ultimately concluded it was not a factor (see their final report here, page 126).
I was skeptical at first, but after doing a Google search — and after NBC reported Sunday that National Transportation Safety Board investigators are “looking at everything” including “the weather” — I think it is a legitimate question to ask.
First, though, why is it an important question to ask? NASA’s James Hansen says we are on the verge of turning the earth into “a different planet” thanks to uncontrolled greenhouse gas emissions. We’ve seen the Brits and Chinese link recent flooding tragedies driven by extreme weather to climate change.
We are all facing far more extreme heat waves, floods, wildfires, rainstorms, droughts and hurricanes — yet our infrastructure apparently can’t handle the weather we have today, as Hurricane Katrina revealed. If we don’t adopt aggressive actions to prevent catastrophic climate change, we need to seriously climate-proof our electric grid, our levees, and our water and sewage systems.
The question remains, do we need to climate-proof our bridges, does a connection exist between climate change and the collapse of the I-35W bridge? Consider what a meteorologist who worked in the city for years blogged:
Now the questions begin. Why did this happen? Structural integrity will obviously be a huge concern. Minnesota experiences extreme temperature fluctuations throughout the year and this summer has been extremely hot and humid. During my time working there, road buckling from extreme heat was very common. You have to wonder if the bridge buckled.
And consider the remarkable conclusion of one Minneapolis resident:
Several eyewitnesses reported seeing what looked like “explosions” coming up from the concrete roadway just prior to the collapse. I am reasonably certain that authorities and investigators will find that the extreme heat of the last several days in Minneapolis had caused the expansion joints in the bridge to close completely. When this happens, the pressure building up between the sections of concrete can amount to thousands of pounds per square-inch.
As the pressure goes beyond the compressive strength of the concrete, the roadway will “buckle”. When this happens on a regular highway, it is a major or minor nuisance, depending upon the size of the buckle. However, a truss bridge is a delicate balance of tension and compression in the structural components.
If the buckling broke this delicate balance and permitted one or both of the vertical members over the piers to shift off vertical (even slightly), a chain reaction would follow that could (and, likely, would) pull down many connecting segments of the bridge on either side of the primary supporting piers. These piers, in this specific case, were about 478 feet apart.
One UK structural engineer said the idea that “hot weather contributed to the accident by weakening the concrete or expanding the steel framework was not a likely explanation, he added, as modern bridges are built to cope with extremes.” But I don’t I think this answers the scenario just laid out, and the question isn’t whether modern bridges are built to cope with extremes, but whether more extremes than anyone might have designed for contributed to the unusual collapse of a “structurally deficient” bridge. As noted, the NTSB itself has not ruled out the weather as a contributing factor.
Melissa Hortman of the Minnesota House of Representatives “speculated that 90-plus-degree heat Wednesday and the above-normal temperatures of the past two summers may have been a contributing factor,” and said “You wonder if this bridge was built to withstand the massive heat we have had this summer.” Or even if it was built to withstand heat, whether its structural deficiencies undermined the design integrity to a point where heat contributed to the collapse.
My brother also wonders if the low level of the Mississippi played a role. He writes that most of “Minnesota is currently under Moderate to Severe Drought conditions. The water level has been lower but the less-than-optimal conditions” could have been a stressor. “Not a cause, but one of the myriad things that can go wrong with a bridge rated among the nation’s worst, one that has been designated ‘structurally deficient‘ since 1990.”
One final point: Some may object to even asking the question, “Did climate change contribute to the Minneapolis bridge collapse?” My guess is those are the same people who deny that global warming is caused by humans or that it is a serious problem — the same people who inevitably say “we can adapt to whatever climate change there is.”
But, in my experience, those “adapters” are actually not interested in finding out what the impacts of global warming are. The Bush administration has blocked research into the impact of climate change on this country and muzzled climate scientists from discussing key climate impact issues, such as the connection between global warming and the recent increase in intense Atlantic hurricanes — which is obviously a central adaptation issue. The latest issue of Time explains, sadly, that this country still isn’t to willing to protect New Orleans from a Category Five hurricane, let alone protect it from a combination of a superhurricane and the sea level rise that is increasingly inevitable thanks to our do-nothing policy on climate change.
Those who argue against strong action today to reduce greenhouse gas emissions — the adapters who are essentially saying to climate change, “Bring it on!” — cannot criticize those who then ask the obvious adaptation question — how will climate change impact this country and its infrastructure?
Certainly climate change will have the biggest infrastructure impact on our coastal cities, water and sewage systems, levees, and electric grid. But given that a remarkable 70,000 other bridges in the country are also structurally deficient, we should seek to learn whether such troubled bridges can take the ever-growing stresses generated by global warming. We need to be as prepared as possible for a changed climate — as the Center for American Progress has previously argued. Indeed, if the adapters have their way in blocking serious efforts aimed at prevention, we’ll need to be prepared for the very worst.
[I'd like to thank my brother Dave for inspiring and helping with this post. You can read all about him here.]