by Judith Curry
Arctic temperatures highest in at least 44,000 years.
A new paper by Miller et al. is getting a great deal of press:
Unprecedented recent warmth in Arctic Canada
Abstract. Arctic air temperatures have increased in recent decades, along with documented reductions in sea ice, glacier size, and snowcover. However, the extent to which recent Arctic warming has been anomalous with respect to long-term natural climate variability remains uncertain. Here we use 145 radiocarbon dates on rooted tundra plants revealed by receding cold-based ice caps in the Eastern Canadian Arctic to show that 5000 years of regional summertime cooling has been reversed, with average summer temperatures of the last ~100 years now higher than during any century in more than 44,000 years, including peak warmth of the early Holocene when high latitude summer insolation was 9% greater than present. Reconstructed changes in snow line elevation suggest that summers cooled ~2.7 °C over the past 5000 years, approximately twice the response predicted by CMIP5 climate models. Our results indicate that anthropogenic increases in greenhouse gases have led to unprecedented regional warmth.
Published by Geophysical Research Letters, [link] to abstract.
From the AGU press release:
The new research offers the first direct evidence that the present warmth in the Eastern Canadian Arctic exceeds the peak warmth there in the Early Holocene, when solar energy reaching the Northern Hemisphere in summer was roughly 9 percent greater than today, said Gifford Miller of the University of Colorado, Boulder (CU-Boulder), who led the study. The Holocene is a geological epoch that began after Earth’s last glacial period ended roughly 11,700 years ago and which continues today.
“The key piece here is just how unprecedented the warming of Arctic Canada is,” said Miller, a geological sciences professor and a fellow at the university’s Institute of Arctic and Alpine Research. “This study really says the warming we are seeing is outside any kind of known natural variability, and it has to be due to increased greenhouse gases in the atmosphere.”
The ice cores showed that the youngest time interval from which summer temperatures in the Arctic were plausibly as warm as today is about 120,000 years ago, near the end of the last interglacial period. “We suggest this is the most likely age of these samples,” said Miller.
The new study also showed summer temperatures cooled in the Canadian Arctic by about 2.8 degrees Celsius (5 degrees Fahrenheit) from roughly 5,000 years ago to about 100 years ago – a period that included the Little Ice Age from 1275 to about 1900.
“Although the Arctic has been warming since about 1900, the most significant warming in the Baffin Island region didn’t really start until the 1970s,” said Miller. “And it is really in the past 20 years that the warming signal from that region has been just stunning. All of Baffin Island is melting, and we expect all of the ice caps to eventually disappear, even if there is no additional warming.”
Temperatures across the Arctic have been rising substantially in recent decades as a result of the buildup of greenhouse gases in Earth’s atmosphere. Studies by CU-Boulder researchers in Greenland indicate temperatures on the ice sheet have climbed 3.9 degrees Celsius (7 degrees Fahrenheit) since 1991.
The region of Northeast Canada (Baffin Island, Ellesmere Island) and west Greenland certainly seems to be a hotspot of recent warming. The west Greenland warming was discussed in the recent post Chasing Ice. I have personally been focussing on the collapse of the Ellesmere ice shelves, which has been quite dramatic in recent years, for a recent summary see this post at Dosbat.
Miller et al. assume that the Baffin Island melting is attributable to AGW. Maybe it is. In the Chasing Ice post, I noted that the peak glacier discharge from West Greenland occurred in the 1930’s. The Ellesmere ice shelves also saw a melt back earlier in the 20th century circa the 1930’s. The Miller et al. paper does not remark on any evidence of warming in the 1930’s, or the LIA or MWP for that matter, but note only a cooling over the past 5000 years, with marked warming in the past 100 years. 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.
In any event, how representative of the Arctic is their findings from Baffin Island? Well, it doesn’t even seem to be too representative even of Ellesmere Island and West Greenland.
There is another paper published almost concurrently, which hasn’t gotten any media attention as far as I can tell, but it does make one think twice about automatically attributing the Baffin warming to AGW:
Eurasian Arctic climate over the past millennium as recorded in the Akademii Nauk ice core (Severnaya Zemlya)
T. Opel, D. Friezsche, H. Meyer
Abstract. Understanding recent Arctic climate change requires detailed information on past changes, in particular on a regional scale. The extension of the depth–age relation of the Akademii Nauk (AN) ice core from Severnaya Zemlya (SZ) to the last 1100 yr provides new perspectives on past climate fluctuations in the Barents and Kara seas region. Here, we present the easternmost high-resolution ice-core climate proxy records (δ18O and sodium) from the Arctic. Multi-annual AN δ18O data as near-surface air-temperature proxies reveal major temperature changes over the last millennium, including the absolute minimum around 1800 and the unprecedented warming to a double-peak maximum in the early 20th century. The long-term cooling trend in δ18O is related to a decline in summer insolation but also to the growth of the AN ice cap as indicated by decreasing sodium concentrations. Neither a pronounced Medieval Climate Anomaly nor a Little Ice Age are detectable in the AN δ18O record. In contrast, there is evidence of several abrupt warming and cooling events, such as in the 15th and 16th centuries, partly accompanied by corresponding changes in sodium concentrations. These abrupt changes are assumed to be related to sea-ice cover variability in the Barents and Kara seas region, which might be caused by shifts in atmospheric circulation patterns. Our results indicate a significant impact of internal climate variability on Arctic climate change in the last millennium.
Published in Climate of the Past, [link] to abstract.
Severnaya Zemlya is in a very interesting location. As per the Wikipedia, Svernaya Zemlya is an archipelago in the Russian high Arctic. It is located off mainland Siberia‘s Taymyr Peninsula across the Vilkitsky Strait. This archipelago separates two marginal seas of the Arctic Ocean, the Kara Sea in the west and the Laptev Sea in the east.
Recall that Kara/Laptev Seas is in the heart of the lynch pin region for the Stadium Wave. Note, Marcia Wyatt did not have any data sets from the Baffin/Ellesmere region of the Canadian Arctic to include in the stadium wave analysis.
Clearly, there is substantial spatial variability of climate variability in the Arctic, with Opel et al. noting a see-saw between the Eurasian vs North American Arctic and seasonal variations (annual vs summer). Especially interesting is the absence of MWP and LIA in some of these high latitude data sets.
In any event, extrapolating from one location in the Arctic to inferring Arctic-wide change is clearly not supported. It further seems that single locations don’t have a very large radius of influence, viz the differences between Baffin and Ellesmere.
The natural internal variability in the Arctic seems to be an exceedingly complex dance between atmospheric circulations, sea ice, ocean circulations and ice sheet dynamics, on a range of timescales. We have some hints about how all this interacts, but much is unknown. In light of this, simplistic inferences about global warming in the Arctic seem unjustified.