“Unprecedented” – skeptic flypaper

“Unprecedented”

Nothing seems to attract the inverted love of fake climate sceptics like the word ‘unprecedented’. Perhaps they don’t like to be reminded that our shared climate trajectory is into unexplored and potentially dangerous space. Perhaps because they can often make the trivial claim that the unprecedented event is not really unprecedented because it was warmer/wetter in the Carboniferous

Miller et al (2013) used this sceptic bait-word in the title of their paper published online yesterday: “Unprecedented recent summer warmth in Arctic Canada”. Miller et al radiocarbon date moss and lichen emerging from beneath glaciers on Baffin Island and find that some are over 40,000 years old. An alarming result implying that the glaciers are now smaller than at any time in the last 40,000 years, and by extension, probably since the Eemian, the last interglacial, ~120,000 years ago. Watts and commentators at WUWT are already attacking the paper with the accuracy and precision of a blind sniper using reindeer droppings for ammunition.

The press release for the paper is characteristically useless, not linking to the actual paper. Unfortunately, despite the interest the media interest the paper was likely to generate, it has not been made open access. This might explain why Watts and commentators at WUWT have obviously not read the paper.

Watts argues that the moss now being exposed by the retreating glaciers may have been previously uncovered and reburied. The paper explicitly discounts this possibility.

Our field observations, and the presence of extensive vegetation-free regions surrounding most retreating ice caps [Locke and Locke, 1976] indicate that most long-dead tundra plants exposed by ice recession are rapidly removed from the landscape by wind-blown winter snow or by run-off during the melt season.

Long-dead mosses and lichen are not the most robust of objects, whereas snow shards blown by a gale are very abrasive, so it is reasonable to assume that the plant remains will not survive more than a few years of exposure.

Watts then dives into a evidence-less discussion on whether the glaciers are melting or sublimating, which would have different implications for the climatic mechanisms responsible for their shrinking. A short search would have led him to Zdanowicz et al (2012) who studied summer melt rates on Penny Ice Cap, Baffin Island. In short, there is lots of melting, more than there used to be, and clear evidence of warming. Watt’s had argued there was no recent warming, wrong again.

Watts ends by whining about the word ‘unprecedented’. The authors claim that the current warming is unprecedented when obviously it was at least as warm 120,000 years ago when the moss grew. Yes, the authors ought to qualify their statement, for example ‘unprecedented in the Holocene’ or ‘unprecedented in the last 120,000 years’, but it is pathetic if this is all Watts has to whinge about.

Several of the commentators at WUWT are complaining that whereas the paper suggests the plant remains are possibly ~120,000 years old, radiocarbon cannot be used to date anything over 50,000 years old . This is of course completely true. The half-life of radiocarbon is 5730 years. After one half-life, one half of the original radiocarbon remains, after two, only half of that amount – one quarter. After eight half lives the amount remaining is 1/2^8 or 0.4% of the original, which becomes difficult to measure as even trace contaminants have a major impact. But this is also entirely irrelevant. If a sample has essentially no radiocarbon, then it must be older than ~50,000 years. Both a lump of Carboniferous coal and an Eemian moss will have a radiocarbon date of ~50,000 years. There is little chance that a the ice melted 50,000 years ago, this was in the middle of a long cool period. The last period plausibly warmer than modern is the Eemian, ~120,000 years ago, so this is the most likely date for the moss.

McIntyre showed up to imply that the radiocarbon dates could be wrong, linking to a paper  that shows that aquatic mosses can have an old carbon effect, where they use radiogenically dead carbon dissolved from limestones and so appear to be older than they really are. Old carbon effects are a major nuisance for dating lake sediments, but are irrelevant here as the mosses (mainly Polytrichum) and lichens dated are not aquatic. The authors also verify that living mosses have a modern radiocarbon age. A large old carbon effect (anything less would not materially change the results) is also not compatible with the large number of lichens <1000 years old.

Others are arguing that the paper cannot be correct because of the Early Holocene Thermal Optimum. However, the Holocene Thermal Optimum, driven by increased summer insolation due to changes in the Earth’s orbit, was probably rather poorly expressed in this region because of the influence of the decaying Laurentide Ice Sheet. Kaufman et al (2004) has a compilation of palaeo data from the Western Arctic showing that the peak terrestrial temperatures in this region were only about 1°C above ‘modern’ (remarkably similar to the cooling found in the CMIP5 model runs reported by Miller et al.). It is perfectly plausible that the climate has already warmed more than this. Curiously, Miller et al estimate that there has been a much larger cooling, 2.7°C since 5000 years ago, from equilibrium line altitudes. Perhaps the albedo from the ice is acting a local positive feedback, amplifying the slight regional cooling.

Still others are indulging in the evidence-free argument that the ice has been melting since the last glacial maximum and has only just receded back as far as the moss collected by Miller et al. This argument is somewhat at odds with the observation that the glaciers and ice sheets expanded between 5000 years ago and the Little Ice Age, and that the ice caps studied are so thin (and can only have ever been thin) that they will melt rapidly under a warm climate.

All these evidence-free and trivially wrong arguments are mixed with a liberal dose of invective and conspiracy theory. Sadly, this is not unprecedented.

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Miller et al (2013) Unprecedented recent summer warmth in Arctic Canada. Geophysical Research Letters