Landscape in a box: How climate can set valley spacing

Credit: Joshua Roering

Credit: Joshua Roering

I haven’t done this very often, but I couldn’t resist a short post on a recent study that connects with the title of this blog.

In many areas where water slices into the surface as it searches for sea level, the landscape is defined by hills creased with sharp stream valleys. There may be broad hills separated by a relatively sparse network of valleys, or valleys and gullies may invade almost everywhere, leaving only narrow bits of high ground. Apart from things like rock/sediment type, geomorphologists have surmised that the difference between those two extremes is a pair of competing forces: 1) the evenly distributed downhill motion of hillslope sediment and 2) the focused erosion of flowing streams in the valleys. If hillslope erosion is stronger, broad hills win out. But if river erosion is dominant, a dense network of valleys will carve up those hills.

That idea is a difficult one to test. If you sit yourself down to watch a landscape change, you’re going to be disappointed. Researchers have used computer simulations to explore this relationship, but that’s not the same as seeing it in the geologic flesh. Kristin Sweeney and Joshua Roering at the University of Oregon, and the University of Minnesota’s Christopher Ellis, took a different tack, building a sandbox model to play with the phenomenon in miniature.

The challenge in building physical models is to get all the forces to scale down, and it’s impossible to pull that off in this case. Although they used very fine-grained silica, the particles are still going to be too big, and the raindrops too large, etc. But even if it isn’t a planet-in-a-box, the model served well as a useful stand-in. Water was dropped onto the sediment in one of two ways: through very fine misters and needle-point droplets. The droplets hit the miniaturized surface like huge raindrops, moving sediment on impact. This takes the place of a number of processes that move sediment downslope, like freeze-thaw “creep”, burrowing animals, tree root wedging, and landslides.  The gentle mist, on the other hand, collected and rolled into gullies to flow downhill. Two sides of the box dropped gradually, creating an ever-lower outlet for sediment-laden water. This is like the tectonic uplift that maintains a steep gradient and makes for rapid streamflow.

During their experiments, “precipitation” alternated between the mist and the droplets for 10 to 15 hours. The researchers varied the proportion of each experiment that water was descending as a mist and as droplets. More mist gives you more valley erosion, while more droplets gives you more diffuse hillslope erosion. A laser scanner frequently mapped the surface of the model sediment to track the progress of landscape erosion.

In experiments where valley erosion was stronger, the result looked like this:

In the experiments where hillslope erosion dominated, however, the result looked like this:

That backs up the theory explaining valley spacing as a competition between stream and hillslope erosion. Not only does that mean that climate controls this striking characteristic of landscapes, but changes in climate and vegetation should lead to an interesting evolution of that landscape. As the researchers write, “Robust linkages between transport processes and topography, as discussed here, are an important component of interpreting planetary surfaces as well as decoding paleolandscapes and sedimentary deposits.” And that’s how a sandbox can tell you about other worlds, and the past of this one.

Science. DOI:10.1126/science.aab0017

Ruminating on a Kentucky farmer

(Sorry about the pastoral pun. I hope you can stomach it. *ahem*)

Dan Kahan, whose research into how the public comes to form opinions on scientific issues reveals the huge importance of our cultural identity and network, has been doing a lot of thinking about a couple enigmatic archetypes: the “Pakistani Doctor” and the “Kentucky Farmer”. (I won’t try to give the entire backstory here, but you can find it via this post.) The Pakistani Doctor, encountered through interviews by researcher Salman Hameed, professes to find evolution important and true in the context of medicine, but rejects human evolution as antithetical to his/her Muslim faith. The Kentucky Farmer, on the other hand, accepts that the climate is changing and alters his farming accordingly, even as he rejects the scientific conclusion that humans are responsible for climate change.

So are these people holding contradictory notions inside their head? How are we to understand their thinking? Dan’s point, as spelled out in the post linked above, boils down to this: these people see no contradiction, and they tell us that the difference between the “evolution” they believe and the “evolution” they disbelieve is context. It’s the cultural relevance. We may be tempted to say, “Yes, but the context is irrelevant— the thing is either true or it is not,” but perhaps we only say that because we successfully pretend that we don’t do the exact same thing. So, in Dan’s view, evolution as it applies to medicine is literally a different concept than evolution as it relates to religious beliefs, and that’s all we need to know to resolve this apparent contradiction. Again, read Dan’s post to flesh this out (and in case I’m poorly representing his argument).

Now, I largely find this insightful and interesting, but a bit of it has continued to stick in my craw, which I promised Dan I would elaborate. I’m going to focus on the Kentucky Farmer. I agree that we should take this farmer at his word when he (implicitly) says that “climate change” with respect to his farm is simply different than “climate change” as it relates to the liberal/conservative point of contention. However, I think stopping there over-reduces what’s going on. The two ideas (of “climate change”), arrived at through the cultural network, come as packets with specific factual baggage. The ideas can differ in content as well as cultural relevance— and if you sit down with the Kentucky Farmer for a beer, I contend it’s highly likely he can tell you all about it. Dan has, of course, thought of this, but seems to have framed it more as a competing hypothesis that comes with rejection of what you might call the “cultural context hypothesis”. I want to push back on that, and argue that this point cannot be left out if you want to fully understand what’s going on.

I’ll rely on my personal experience with the Wisconsin farmer, as I think I’m justified in believing these attitudes to be broadly shared. The Wisconsin farmer has also noticed the unusual weather of recent years, and attests that the current climate differs from the one his father worked with. So yes, you’d better believe he’s willing to adjust his practices. And no, he’s not willing to pin this change on human activities— he finds that hard to believe, so who really knows? And besides, he knows the weather is an unpredictable beast prone to mood swings. Things go up, and things go down, and that’s just how it works. It’s been warmer and drier lately, and someday it will probably be cooler and wetter again. Everything goes in cycles, you know? He’s happy to plan for next summer based on the last ten, because what else can you do?

The “climate change” he rejects isn’t just the liberal variety (context), it’s also different (content).  That climate change is the result of SUVs, coal power plants, and is supposedly going to get warmer and warmer and warmer until there’s some kind of doomsday, according to Al Gore. Here’s the key: ask him what he thinks the climate will be like in 60 years. Does he need to make changes to his farm to ensure his kids’ success? I can almost guarantee he’ll say, “Oh, who knows, maybe warmer, maybe cooler. I wouldn’t get too carried away.” If he truly accepted the reality of climate change as it relates to agriculture, he wouldn’t hesitate to bank on further warming, but that’s not what the “climate change” he accepts means to him. (Might he deny that “global warming” is a synonymous label for his “climate change”?) These things are factually distinct.

This will exhibit itself in his policy preferences. He may support policy that helps farmers adapt to (cyclical, unpredictable) climate change. He will not support policy that actually addresses the cause and mitigates it, because he doesn’t believe in that kind of climate change.

So while I think it’s really useful to consider the fact that we can think differently about a concept if it occurs in multiple contexts, I think we have to wrestle with the fact that in some cases these concepts will be sculpted into distinct things— either by our own reasoning or via our cultural network. Dan has written that it can be almost condescending to decree that the Kentucky Farmer is contradicting himself, and to demand a solution to his foolish paradox. However, I think it can also be condescending to stop him when he gives us one reason why he doesn’t feel he’s contradicting himself— he may not be done explaining things he has put a lot of thought into. I don’t think what I’ve outlined above superficially “explains away the paradox”, as Dan put it, any more than the “cultural context hypothesis” does so. It’s just digging far enough into the details to be sure we understand what the Kentucky Farmer is telling us.

I don’t think we can really celebrate the Kentucky Farmer’s willingness to accept “climate change” as it relates to his normal, everyday business, because he’s not accepting the same facts we’re concerned about. We may find it illustrative to discover how his “climate change” has been sculpted to become culturally palatable, though. Why is he willing to accept those facts/beliefs? We can come up with plenty of plausible reasons. (Perhaps human/divine control of nature, perhaps opposition to regulations on markets or government control, etc.)

However, we shoudn’t expect that he will necessarily be amenable to our version of “climate change”, given the right context. Context may not be the only thing that allowed his “climate change” to pass through the cultural filter.

Once more: McPherson’s methane catastrophe

For better or worse, I want to briefly  return to Guy McPherson’s claims of human extinction within 20 years via a climate catastrophe. Guy is aware of my criticism of his argument, but has declined to consider the problems I pointed out (instead choosing to accuse me of being paid to disagree with him, which would be news to my bank account). Because I’ve seen him reduce his climate claims to the same two keys a few times now, I thought it might actually be worth singling them out for detailed inspection (even though both are mentioned in my previous post, which was a little overwhelming). I’ll try to keep this simple, but the desire to be thorough can make that a challenge…

(Runaway) Train to Siberia

The first claim is that there is an incontrovertible, rapidly accelerating release of methane from the Arctic. (Example here.) McPherson ascribes this to a destabilization of methane hydrates (also called clathrates) in the sediment beneath the Arctic seafloor. Ostensibly, this is based on the research of a team including Natalia Shakhova that has been studying methane release along the East Siberian Arctic Shelf, but McPherson’s claims about that research come from posts on the “Arctic News” blog. This blog, run by a retired petroleum geologist named Malcolm Light and someone writing under the name of Sam Carana, posts a great deal of strange and unscientific claims about earthquakes and methane in the Arctic.

Specifically, McPherson points to a post there interpreting the Shakhova et al. research as indicating an exponentially-growing release of methane from the East Siberian Arctic Shelf. Apart from the fact that two data points can’t  tell you there’s an exponential trend (rather than, say, a straight line), this also makes the mistake of assuming that there are actually two data points! What really happened is that the Shakhova group tried to estimate the total annual emission of methane from the East Siberian Arctic Shelf after observing some plumes above focused release points. (It’s not yet known if these releases have increased recently— the submerged permafrost has been thawing for thousands of years, since sea level rose coming out of the last ice age.) A couple years later, they published a new estimate based on expanded observations. This was a revision of their earlier estimate, now that they had more data in hand. Sam Carana treated these two estimates as independent numbers representing a time series— asserting that the emission of methane had more than doubled in just a few years. From there, Carana extrapolated to predict that emissions would increase about 1,000 times over by 2040. As a result, he/she predicts a cartoonish increase in the global average temperature of 11 C by 2040. (Actual climate models, on the other hand, project a temperature increase of around 4 C by 2100 if we fail to reduce greenhouse gas emissions— and that’s a deeply troubling scenario.)

Actual measurements of methane in the atmosphere don’t show any such sudden, accelerating spike, and climate scientists don’t believe anything like this “clathrate gun” scenario is underway. The Arctic News Blog obsesses over some satellite measurements of methane in the Arctic, believing that they support the claim of runaway methane emissions. (A researcher who worked on validating that satellite dataset confirmed to me that the raw data the blog is using hasn’t been through any quality control algorithm, and that the instrument hasn’t been validated for some of the kinds of conclusions Carana wants to draw.) By showing that some recent measurements of methane in the Arctic are above the global trend, they believe they are demonstrating a sudden increase. This is misguided, because the Arctic is always above the global average. That’s why we calculate averages. If you measure CO2 in the smokestack of a coal-burning power plant and find that it’s much higher than the global average from last week, you can’t conclude that is CO2 suddenly spiking globally. That sort of apples-to-plastic-oranges comparison is meaningless.

So when McPherson claims that “the clathrate gun has fired“, he does so without any evidence whatsoever. Rather, he relies on elementary mistakes made by a blogger who doesn’t appear to understand the science. Not data. And not published research. Not only do climate scientists not think that such a thing is underway, most don’t think it’s likely to be a worry this century.

Do the D-O

The second claim is that Paul Beckwith, a PhD student at the University of Ottawa, predicts 5 – 16 C of global warming within a decade— or, in a softer version, that Beckwith believes such a warming event could occur within a decade in the near future. McPherson continues to make this claim, despite the fact that it has repeatedly been shown to him to be inaccurate. To be fair, Beckwith has stated the second version of this— that such a thing could happen. However, Beckwith also appears to be confused. (I tried several times to get this straightened out with Beckwith, but haven’t had any luck.)

Beckwith has been referring to climatic swings called Dansgaard-Oeschger events identified in Greenland ice cores that occurred every 1,000-2,000 years during glacial periods (“ice ages”). During the abrupt warming phase of these events, the cores record 5-17 C warming in as little as a decade. Following that jump, temperatures gradually dropped over the following centuries. Dramatic as they are, they are not swings in global average temperature, but swings in local Greenland temperature. (This is what ice cores record.) Dansgaard-Oeschger events are terrifically interesting, and there has been a lot of research focused on understanding them. While there are still competing hypotheses for their cause, it’s generally agreed that they involve changes in the large-scale circulation of the Atlantic Ocean— what’s called the Atlantic Meridional Overturning Circulation (AMOC). In the North Atlantic, cooled, salty surface water from the south mixes downward and returns southward at depth. This movement has a large impact on temperatures around the North Atlantic, and the downward mixing that drives the circulation is relatively sensitive, meaning that it can be slowed or jammed up. One way to do that is by increasing the input of freshwater from melting glacial ice, decreasing the density of surface water.

It’s possible that messing with the AMOC could shrink the extent of sea ice off Greenland’s eastern coast, which would help explain the rapid and large temperature shift recorded in the ice cores there. Regardless, the shift would have been largest in Greenland, smaller around the rest of the North Atlantic, with only knock-on effects (mainly in precipitation) beyond that. (That said, CO2 did slowly rise about 10 ppm before some D-O warming events and drop after— a product of ocean circulation change— and methane did increase a couple hundred ppb over a few centuries around them— probably due to wetlands.) The point is that they are not instances of global warming, they are regional events. Noting that Greenland rapidly warmed 5-16 C over one or a few decades in the past does not imply that the entire globe could do the same thing today. In order to change the average global temperature so significantly, you have to alter the planetary balance of incoming and outgoing energy in a big way. That didn’t happen during the Dansgaard-Oeschger warming events. Given that these events seem to entail changes to the Atlantic Meridional Overturning Circulation, they’re really not analogous to the greenhouse-gas-induced global warming we’re currently experiencing. They’re certainly not analogous to the methane hydrate catastrophe scenario that McPherson is preaching. Beyond that, there’s likely a good reason they only occurred during glacial periods and aren’t likely to occur now. The latest IPCC report, for example, judges a sudden shutdown of the AMOC this century “very unlikely“.


McPherson seems to think that these two points are his strongest, but there’s really nothing there to support his eschatalogical message of imminent human extinction— and those who aren’t sure what to make of his dire claims should take that into consideration. If we listen to climate scientists, instead, we find more than enough justification for immediate action on climate change without resorting to sci-fi-like exaggeration. And action would be a lot more productive than sitting around waiting for an extinction that isn’t going to show up on the date circled on your calendar.

The tragedy of “environment” as a political word

In cultural battles, as most of us can attest, things get emotional. Small things can set people off. Complex issues get simplified down to bite-size kernels that mainly serve to separate Us from Them. There are trigger words, pregnant with meaning— often pregnant with twins. Which meaning is the is evil, mustachioed one depends on who you ask. Sometimes the triggers are invented for the battle, but other times innocent, important words get pulled into the fray. And that can be a tragedy.

One such tragedy besets the word “environment”, and confusion about the definition hasn’t helped. The environment, of course, is everything on this planet we call Earth. It’s everything around us. It’s the air we breathe in town and the air we breathe in the country. It’s the water that comes out of our taps; it’s the waters we photograph on vacation. It’s the squirrels on our birdfeeder and it’s the predators we listen to David Attenborough describe on TV. But to many, it’s just something “out there”. National parks. National forests. Antarctica. The Amazon.

Taken that way, “save the environment” gets parsed as “help some trees somewhere at the expense of people”. Those naive tree-huggers, ya know? That framing underlies a great many environmental debates, whether that’s the restoration of wolf populations or the maintenance of water flows to sustain fish populations.

And that’s the railroad switch that sends even the word “environment” down different tracks. It’s hard to find someone who doesn’t appreciate the beauty of wild places. It’s even harder to find someone who doesn’t want healthy surroundings. And yet, it’s now nearly a cultural fact that “environment” is a word for far left-wing liberals. Being a conservative— or maybe even a moderate— means disregarding this “environmental agenda” for far too many people. Get too close to something “environmental” and you could lose your cultural credibility. That makes it even harder to get people to see that the environment is not separate from the world in which they live, and that, in fact, their life and prosperity depends entirely upon it.

We can’t have serious discussions about how to protect the things we all enjoy and depend on because our words straddle cultural lines in the sand. That toxicity even prevents us from using other words to connect on common ground, because we are quick to retreat to the same old, tedious, fighting. It’s ignorant science-deniers vs. ignorant bleeding-heart hippies. Land punches. Score points. You already know there’s no talking with these people.

“Environmentalist” shouldn’t be a contentious description any more than “pro-children” or “anti-house-fire”— and we shouldn’t really need any of them. Unfortunately, groups like ConservAmerica still have their work cut out for them, as do we all.