Since I discussed the presumed Eemian mosses being exposed on Baffin Island discovered by Miller et al (2013) and the clueless response from WUWT, I’ve seen that others are discussing this paper, including Steve McIntyre, Judith Curry, and Jim Bouldin.
Curry’s contribution can be summed up as
The reasoning behind the Miller et al. conclusions is rather complex, with a number of assumptions, I’m not sure what to make of their arguments.
Both Bouldin and McIntyre comment that at some of the icecaps’ margins, the moss appearing from under the melting ice is mid-late Holocene, at others it is >~40,000 years old, presumably Eemian. For example, from McIntyre,
A question: How does one reconcile the supposed in situ continuity of the little “ice cap” in the vicinity of sample M10-B231v (1395 m) since 44000 BP with recession in the vicinity of nearby higher M10-B226v (1438 m)?
Let’s get the virtual crayons out to try to explain what is happening.
The Eemian (strictly some time prior to ~40,000 years ago) was warmer than the Holocene because the Earth’s orbit was different leading to higher solar insolation during summer. Mosses and lichens grew across the mountain top.
Following the Eemian, the Earth’s orbit changes, summer insolation decreases, the climate cooled and an icecap developed on the mountain top, preserving the mosses beneath it. Because of the shape of the mountain top, the maximum thickness of ice that can accumulate is ~70m (any more and the ice flows over the edge of the summit plateau).
During the Early Holocene, much of the icecap melts under the high insolation at the time (but not as high as in the Eemian). Eemian moss remains preserved under the icecap, Early Holocene mosses grow around it.
The climate cools in the late Holocene as summer insolation deceases in the Arctic. The icecap grows again. Eemian mosses remain preserved under the centre of the icecap under ice from the last glaciation. Holocene mosses are preserved nearer the periphery under late Holocene ice. The Holocene mosses are not those that grew at the thermal maximum, but the last ones to grow before the icecap overwhelmed them.
The 5,000 year long cooling trend is reversed in the 20th Century under the influence of anthropogenic forcings. At some parts of the ice margin, Eemian mosses are exposed, at others mid-late Holocene mosses are exposed. This is what concerns Bouldin and McIntyre.
First, it should be noted that the inner-most mid Holocene moss will be very close, perhaps less than a metre, away from the outermost, Eemian moss. So unless ice accumulation and melting occurred in a perfectly symmetrical pattern, it is expected that as the first Eemian mosses are being exposed from under one margin of the icecap, mid-Holocene or later mosses are being exposed from under another. In reality, ice accumulation and melting will be far from symmetrical on these icecaps: both will depend on the slope, aspect and situation. Snow and ice accumulation will be fastest on the lee side of the icecaps, where there is some slight protection from the prevailing wind; melting will be fastest on south and south-west slopes that receive the most solar insolation. So some areas will have accumulated much ice during the late Holocene, other areas rather little. It is implausible that 20th Century melt would perfectly compensate for this, melting the high accumulation areas faster so that Eemian moss is exposed simultaneously in all areas. Of course, one could do a couple of PhD’s worth of research to explain the fine details of the ice accumulation and melt on Baffin Island’s ice caps so we perfectly understand why some ice margins are exposing Eemian mosses, other late Holocene mosses. Another few years delay wouldn’t do any harm would it?
It is also worth noting that the icecaps are far from equilibrium with climate – they are, or at least were in the period 2000-2005, melting 0.5m/year. Such rapid melting implies that the icecap will shrink further should the climate remain warm, potentially melting all the ice.
One potential confounding factor, not covered by any discussion I have seen about this paper, is the role of black carbon changing the albedo and hence melt rate of the ice. However McConnell et al (2007) show from ice core records, that black carbon deposition on Greenland peaked between 1900 and 1950, before declining substantially, so this is probably a relatively minor issue.