November 2013
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Were the floods tied to climate change?

By Peter Miesler

Colorado experienced its most extreme weather event in recent memory between Sept. 9 and 15. Golden, Boulder and Larimer counties received the worst of it, with rain accumulations of 16-17 inches and more. Some areas received nine inches on Thursday alone, resulting in massive flooding compounded by destructive run-off from mountainsides with burned-out forests that could no longer hold water.

Predictably, folks are asking: Is this related to man-made global warming?

That a question that is both easy and tough to answer.

Our climate system is a global heat-distribution engine and our land, atmosphere, and the oceans have indisputably warmed. Not only that, our atmosphere’s moisture content has been measurably increasing. Given such geophysical realities, it is self-evident that all extreme weather events contain elements of this newly energized climate system. And that much more of the same must be expected.

So in that sense, the answer is easy: Yes.

On the other hand, this is an exceedingly difficult question to answer if the demand is to know precisely every attribution down to fine details.

Fortunately for interested citizens, scientists have been trying harder to convey their knowledge of those details.

For example, less than two weeks after the flooding, the Western Water Assessment (WWA) together with the Cooperative Institute for Research in Environmental Sciences (CIRES) released a preliminary report during an hour-and-half-long videoed web news conference. (Both can be found at wwa.

The CIRES/WWA event was a collaborative effort among many people and interconnected agencies, including NOAA’s ESRL (Earth System Research Laboratory) Physical Science Division, and the Colorado State University’s Climate Center. It was a good example of scientists sharing their data and discussing the state of their science, including all the gaps, flaws, inconsistencies and uncertainties they perceive.

Watching the Sept. 25 presentation, I was reminded what a straightforward, conservative lot scientists are. They will say what they know for “sure” and stop. Then they will back-track and share every doubt they have in order to prove that they do indeed understand weaknesses and further questions regarding their area of study.

The report, “The Unusual Weather Pattern,” explained that “the extraordinary rainfall in this event was due mainly to the unusual and persistent weather pattern that funneled abundant moisture towards the Front Range and enhanced the lift.”

To understand what this means, you need to know about the polar jet stream, a highspeed ribbon of air that’s driven by atmospheric temperature differentials between Earth’s hot tropics and cold polar regions. It’s been there for millennia, whipping around the Northern Hemisphere, pushing and pulling weather patterns with it.

You see, one result of our society “salting” our atmosphere with greenhouse gases is that the atmosphere’s insulating ability has increased. That’s because these atmospheric gases catch Earth’s heat waves as they rise towards frigid outer space. More greenhousegas molecules means catching more heat, so the planet warms.

Since the industrial revolution, society has increased that greenhouse-gas component by about a third, causing the Earth to retain more heat within our climate system than it used to.

One of the cascading consequences of this is that the polar atmosphere is actually swelling and changing its relative elevation. This, in turn, causes a decrease in the differential between polar and tropical regions. This has manifested itself in a slower and more meandering jet-stream pattern, which has been at the root of some very extreme events such as the September rains and floods in Colorado.

What happened was that in mid-September, Colorado got stuck between two such stalled jet-stream loops for about a week before they moved on.

Technically, and to quote the University of Wisconsin-Madison’s Cooperative Institute for Meteorological Satellite Studies (CIMSS), what happened was that in the upper atmosphere above the Great Basin west of the Rockies, a “quasi-stationary upper-level cyclonic circulation” developed, while across the mountains, over the Great Plains, a “lower-tropospheric anticyclonic circulation” pattern set in.

Meanwhile, down south off Baja California, tropical cyclone Lorena was dissipating. The two stalled circulation patterns started sucking all that tropical moisture right into Colorado. It then got funneled up the mountain slopes, saturating the air to record-breaking levels, and dropped out of the sky in a “biblical” deluge.

All this information was explained in wonderful detail.

But then, disturbingly, when a reporter asked pointedly about the global-warming connection, these geophysical facts suddenly became “speculation” subject to further study.

Using a freak, but similar, Colorado event back in September 1938 as justification, Dr. Martin Hoerling of the National Oceanic and Atmospheric Association rejected making any firm connection to global warming, saying we need further study. As I understood him, he also felt we needed a more accurate understanding of past extreme weather events.

I was left wondering, what good is seeking a time-consuming “perfect understanding” of past events when the atmosphere’s composition at that time was radically different from today’s? It’s nice to know, but it is background information and not that relevant to our contemporary climate, which has been and continues to be supercharged.

Beyond that, I found it odd Dr. Hoerling used one 1938 freak event to warn against making premature assertions. Why not acknowledge the recent cascade of “jet-stream blocking pattern”-driven extreme events such as the record-shattering European heat waves of 2003, 2006, and 2011 and the Russian heat wave of 2010, and the floods in Russia and Pakistan in 2010, and the recent Calgary floods and the extreme winters on the East Coast three and four years ago?

In fact, I wrote Professor Hoerling and asked why he seemed to reject all the studies that have shown evidence for global warming- driven Arctic amplification influencing the jet stream, such as those being reported by Dr. Jennifer Francis of the Institute of Marine and Coastal Sciences and colleagues. Unfortunately, I didn’t get a response, but in fairness he is a very busy man.

Still, I find it disturbing when scientists, who are supposed to inform and advise leaders and the public, slip into that professorial deep-thought mode and focus on minutiae while ignoring the big picture.

The professor is typical of many conscientious scientists. Statistical certainty is their calling – but from my boots-on-the-ground perspective, statistical certainty does not trump the laws of physics, nor the geophysical reality we are actively altering. Are the exact details really that important? Doesn’t a basic climatology outline tell us enough to know we need to stop denying and start collectively getting real about what is happening out there?

Peter Miesler writes from Durango, Colo., and has a blog at

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