Humboldt squid

Megan McArdle is a libertarian who is basically sane, so she is not a global warming denier or anything. However, comments like this strike me as missing the point:

What's at stake is the degree of warming associated with our carbon dioxide emissions. In particular, to what extent the earth's many complex and not necessarily well understood feedback systems may mitigate (or exacerbate) temperature increases. I've long been skeptical of the more catastrophic scenarios, because all this carbon used to be in the atmosphere, which probably defines a ceiling on how bad it will get--a ceiling well below "WE'RE ALL GOING TO DIEEEEEEEE!!!"

I think she's narrowing in too much on the temperature aspect here. While it's true that earth has "many complex and not necessarily well understood feedback systems" that determine what the average global temperature will be, what is really relevant here is that the biological environment is made up of even more complex and even less understood systems, and we simply can't predict what all of the consequences will be for these systems if and when the global temperature shoots up. To invoke some Rumsfeldese, there are known unknowns and then there are unknown unknowns. It is the unknown unknowns that really make global warming such a serious threat--the stuff that no one could have predicted.

Personally, when I envision ecological disruption from climate change, it's something along the lines of the Humboldt Squid takeover of the North Pacific. The story here is that since 1960 the numbers of this kind of squid has exploded, altering the ecosystem so that fisheries for "anchovies, sardines, hake and rockfish"--all species that the squid feed on--are threatened. They theorize that nitrogen-rich farming runoff is causing a favorable environment for the squid, but the region in which they dominate continues to expand, and nobody knows why:

In the KQED-TV story, Gilly says that the OML [oxygen minimum layer] may be growing -- getting thicker and coming closer to the surface. And where the OML grows, the squid follow.

Nobody knows why the OML is growing, though. Does it have something to do with climate change? Is it related to agriculture? It would be handy to know.

This is the kind of thing we should be envisioning, I think, when we talk about the dangers of global warming--stuff like, oh shit, now squid are taking over the ocean. Of course, in this particular case the success of the squid isn't really too disruptive (besides endangering some fisheries, the article doesn't seem to be too worried about any of it), but the point is that this is the type of system that's being affected, and these are the types of consequences we can expect to encounter as global temperatures rise.