May 25, 2006

More Evidence of Arctic Warmth (a long time ago)

There are a lot of folks running around shouting that recent Arctic warming is, to use a favorite alarmist word, “unprecedented”—which means, to them at least, that we are approaching “dangerous” levels of climate change. It seems a bit odd to equate “unprecedented” with “dangerous,” since the former implies something that is novel, while the latter implies something that is known. So, for instance, since we know that for a good 90% of the past 400,000 years the earth was locked into ice age conditions, it would seem that a “precedented” cooling would be perceived to be far more “dangerous” than an “unprecedented” warming, wouldn’t it? But we digress.

In any case, how close to being “unprecedentedly” warm are we in our northerly latitudes? (We focus here on the Arctic because the Antarctic has been cooling for the past several decades, so that pretty much eliminates temperatures there from being unprecedented).

The answer, not very.

In fact, today’s temperatures aren’t even close to being “unprecedented.” Writing in the journal Quaternary Research, Jason Briner from the Geology Department of the University of Buffalo and a host of colleagues from the United States and Canada state:

This study offers a high-resolution lacustrine Holocene climate record that spans the last ~11,200 years. The most notable feature of Holocene climate at Lake CF3 [ located on Canada’s Baffin Island] was the well-defined HTM [Holocene Thermal Maximum] between ~10,000 and 8500 cal yr B.P., when chironomid-inferred summer temperature was ~5ºC warmer than today and the duration of seasonal lake ice cover probably was the shortest since deglaciation.

Putting this finding in context, Briner et al. continue,

Pollen records from several Baffin Island lakes indicate middle Holocene temperatures ~1 or 2ºC warmer than present (Kerwin et al., 2004). Because pollen-based temperature reconstructions rarely extend beyond 7 or 8 ka [thousand years], they may not capture maximum Holocene warmth. Chironomid taxonomy- and δ18O-based summer temperatures from Qipisarqo Lake on southern Greenland indicate that conditions were 2 to 4ºC warmer in the early Holocene versus the late Holocene (Wooller et al., 2004). Diatom-inferred temperature data from Fog Lake, ~420 km south of Lake CF3 , reveal a ~4ºC difference between the middle and late Holocene (Joynt and Wolfe, 2001). Dynocyst assemblages from northern Baffin Bay marine cores reveal ~5ºC difference in sea surface temperature (SST) between the middle and late Holocene (Levac et al., 2001). Greenland ice sheet borehole paleothermometry indicates a temperature change of ~3.5ºC between the middle and late Holocene (Dahl-Jensen et al.,1998).

So, Briner et al.’s results add to a large amount of evidence that conditions in the Arctic were several degrees warmer than present during extended periods since the end of the last ice age (the “holocene” era). And if you think that this only applies to the region around Baffin Island, think again. UCLA’s Glen MacDonald and colleagues reported this, a couple of years ago, in the same journal,

Radiocarbon-dated macro fossils are used to document Holocene treeline history across northern Russia (including Siberia). Boreal forest development in this region commenced by 10,000 yr B.P. Over most of Russia, forest advanced to or near the current arctic coastline between 9000 and 7000 yr B.P. and retreated to its present position by between 4000 and 3000 yr B.P….During the period of maximum forest extension, the mean July temperatures along the northern coastline of Russia may have been 2.5º to 7.0ºC warmer than modern.

And Darrell Kaufman from Northern Arizona University and his colleagues took a comprehensive look at research performed over the remainder of the Arctic and summed things up in Quaternary Science Reviews as,

The spatio-temporal pattern of peak Holocene warmth (Holocene thermal maximum, HTM) is traced over 140 sites across the Western Hemisphere of the Arctic (0–180ºW; north of ~60ºN). Paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer-than-present conditions at 120 of these sites. At the 16 terrestrial sites where quantitative estimates have been obtained, local HTM temperatures (primarily summer estimates) were on average 1.67±0.8ºC higher than present (approximate average of the 20th century), but the warming was time transgressive across the western Arctic. As the precession-driven summer insolation anomaly peaked 12–10 ka (thousands of calendar years ago), warming was concentrated in northwest North America, while cool conditions lingered in the northeast. Alaska and northwest Canada experienced the HTM between ca 11 and 9 ka, about 4000 yr prior to the HTM in northeast Canada.

So there you have it. Based upon the scientific literature, it would appear that rather than approaching an era of “unprecedented” temperatures in the Arctic, we are fast approaching and era of “unprecedented” hype.

We certainly hope the folks responsible for putting together the new Fourth Assessment Report (AR4) of the U. N.’s Intergovernmental Panel on Climate Change (IPCC) are taking notice of these developments.

References:

Briner, J. P., et al., 2006. A multi-proxy lacustrine record of Holocene climate change on northeastern Baffin Island, Arctic Canada. Quaternary Research, 65, 431-442.

Kaufman, D.S., et al., 2004. Holocene thermal maximum in the Western Arctic (0 to 180W). Quaternary Science Reviews, 23, 529-560.

MacDonald, G.M., et al., 2000. Holocene treeline history and climate change across northern Eurasia. Quaternary Research, 53, 302-311.




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