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“.

So…

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.