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Wednesday, December 17, 2014

XKCD: Randall Munroe gets it all laughably wrong

What If - what if all the rivers in the US were instantly frozen in the middle of summer?

It's amazing how much wrong there is in this article.

Let's conduct a thought experiment: imagine there's some strange unknown part of the world where the rivers freeze every year.

Like how's about nearly all of Canada.

And then let's extrapolate Canada's yearly experiences to see how wrong Munroe is.

We can use data on iceberg melt rates to estimate how quickly individual rivers would melt. Small streams would melt in days in all but the coldest areas, while ice in larger rivers would take longer.
Or how's about instead you look at how fast rivers actually melt in Canada, in the early spring when the temperature is just above freezing and the ground is still frozen solid, and then extrapolate to how much catastrophically faster they'd melt in the summer, in the US with more insolation, and with more heat transmitted from the warm ground, and with that sanity check realize that your iceberg melt rates don't provide any useful information whatsoever here?

Rivers melt fast. Catastrophically fast. It is a runaway phase change.
To help me out with this question, I talked to Charlie Hohn, a Vermont field naturalist with an interest in river behavior. I brought Zoe's question to him, and he made a lot of interesting observations.

He pointed out that the water feeding into the rivers—from tiny rivulets and raindrops and melting snow all over the watershed—would suddenly find its path blocked by a wall of ice.

But all that water still has to go somewhere. And if the riverbed is full, it will go somewhere else.

"Any place with rain or snowmelt would have horrific flooding because the water would have nowhere to go," Charlie told me. "Water would shoot down narrow canyons, and once it hit the floodplain it would probably jump into old river channels where they exist, but in many areas that would mean towns and farms."
Are you sure he comes from Vermont? Cuz up here in Canada we don't get "horrific flooding", despite our thawing rivers getting fed with an entire season's worth of snowmelt in just a couple days.

We get melt surges, but they're nothing major. See, water flows. Water goes around ice, and the more warm water flow you get the faster the ice melts. And water does a great job transferring heat from ground to ice.

Then again, yes the entire world knows that you Americans have this weird propensity to build entire cities in flood plains.
Charlie notes that even a small ice dam can cause terrible flooding. When the Winooski river in Vermont was clogged by an ice dam in 1992, the water spilled over the banks and flooded Montpelier in a matter of minutes. And that's just a tiny river, he says. "The Winooski here is narrow enough to throw a rock across, and usually only a few feet deep. In a dry year you could wade across in summer in shorts without getting them wet. So scale that up to the Mississippi and 12-foot-thick ice."
Are the people in Vermont so stupid as to not know how to break an ice jam? Is brain damage mandatory up there? Or do you just not believe in governments hiring people to manage rivers? They let you maniacs down there play with guns, why not dynamite?
"If there were salmon in the rivers, the bears would feast on them when they thawed. But later, if the fishery crashed, there would be a bunch of desperate hungry bears unleashed on the environment."
Randall, are you sure this guy's not just shitting you? Because up here in Canada we're not getting eaten by hordes of desperate angry bears every year. Seriously, the only people ever eaten by bears in Canada are stupid German tourists.
We'd probably limp through the scenario tattered but alive, buying food overseas.

I damn well dare you to do the math, Randall. Because I'm pretty certain that, "in the middle of the summer", even a completely frozen-solid Mississippi would (at its largest cross-section) melt completely in 2-3 days.

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