Since we are in the season of comparing charts, graphs and interpretations of the summer Arctic ice melt, it may be useful to pause and consider the history of Arctic temperatures in the Holocene. There is an abundance of data compiled by hardworking field researchers over the years. Before everybody got so excited about global warming, it was understood that the Arctic was considerably warmer in earlier parts of the Holocene than in the present. The evidence for these warmer periods seems to have been forgotten in an age when satellite data causes us to fixate on the last thirty years.
I have collected a short list of papers that indicate times during the mid-Holocene, and places in or near the Arctic, when it was warmer than the present. Some of these papers may also indicate warmer periods in the early or late Holocene, but I am concentrating primarily on the mid-Holocene in this post. Figure 1, below, shows the spatial distribution of areas covered by these papers. Click on the image to get a larger view. Figure 2 shows the times in the mid-Holocene that each paper says it was warmer than the present.
Figure 1. Numbers correspond to the journal articles that are listed below. They also correspond to the numbered lines in figure 2.
Figure 2. “Paper #” corresponds to the numbered journal articles listed below. The colored areas indicate the time periods in the mid-Holocene for which the papers indicate it was warmer than present.
The evidence that the Arctic was warmer in the mid-Holocene than it is now is compelling. At longitudes almost completely encircling the Arctic, palaeological proxies of all kinds speak from the past with the same message. Treelines moved in latitudes and elevations. Alkenone molecules produced from sun loving organisms in the top layer of ocean water recorded the temperature of the water and settled into the depths of the ocean, depositing their temperature record in the sediments. The pollens of various species of plants changed their ratios with changing temperatures and forest locations, drifted over lakes and settled to the bottom, leaving layer upon layer of temperature history. Choronomid midges, small insects that live out their short lives in just a few weeks, varied their physiology according to the temperature of their environment, and carried their temperature stories to lake sediments. Forest plant species came and went at temperatures rose and fell, leaving behind their seeds in successive layers of soil as positive reminders that they had been there.
These proxies, and others, strongly indicate that the arctic region was warmer around 5,000 years ago than it is today. Read the papers listed below to see the details.
Please feel free to criticize my interpretations of the papers, or to point out contradictory or complementary papers.
1. Jung-Hyun Kim, Norel Rimbu, Stephan J. Lorenzb, Gerrit Lohmanna, Seung-IlNam, Stefan Schoutene, Carsten Ruhlemannf, Ralph R. Schneiderg, North Pacific and North Atlantic sea-surface temperature variability during the Holocene, Quaternary Science Reviews, 23, 2004
Kim, et. al., used alkenone-derived sea-surface temperature records from sediments from over 30 locations to derive temperature changes in the Pacific and the Atlantic Oceans during the Holocene. I have marked the locations of the five highest northern latitude cores, two above the arctic circle and three below it. Kim’s data for these cores covers only the last 7,000 years, rather than the entire Holocene. Nevertheless, the cores show temperatures clearly dropping to modern values over the last 7,000 years. The northern-most core (75N) shows a temperature drop of 4.4 degrees C since 7,000 years ago. Two other cores show temperature drops greater than 3 degrees C (3.3 and 3.8 degree drops at 57.8N, 8.7E and 57.7N, 7.1E respectively). The remaining two cores show temperature drops of 1.8 and 0.6 degrees C. Get copy here.
2. Kultti, S., et. al., Past changes in the Scots pine forest line and climate in Finnish Lapland: a study based on megafossils, lake sediments, and GIS-based vegetation and climate data,” The Holocene, Vol 16 No3, 2004b.
In this paper, Kultti, et. al., (2004b) looked at tree lines in Finnish Lapland and found “Results indicate that pine reached its maximum distribution between 8300 and 4000 cal. yr BP. The inferred minimum shift in mean July temperature was at that time c. +2.5.” Get copy here.
3. Solovieva, N., and Jones, V., A multiproxy record of Holocene environmental changes in the central Kola Peninsula, northwest Russia, Journal of Quaternary Science, 17(4), 2002.
Solovieva and Jones studied a multi-proxy record of the Kola Peninsula in northern Russia and concluded that for the period from 8000 years ago to 5400 years ago “A maximum of forest cover and the high Pinus abundance during this period indicate the Holocene climate optimum. The multiproxy data from Chuna Lake generally agree with the temperature reconstructions based on the evidence from the Greenland ice-cores (Stuiver et al., 1995) and summer temperatures were likely to have been 2°–3 °C higher than at present.” Get copy here.
4. MacDonald, G., et. al., Radiocarbon dated Pinus sylvestris L. wood from beyond tree-line on the Kola Peninsula, Russia, The Holocene, Vol. 10, No.1, 2000.
MacDonald, et. al., dated Scots Pine wood (Pinus sylvestris L.) in Russia’s Kola Peninsula and found “the density of trees north of the modern tree-line was greatest between 7000 and 5000 BP. Get copy here.
5. Sarnthein, et. al., Centennial-to-millennial-scale periodicities of Holocene climate and sediment injections off the western Barents shelf, 75°N, Boreas, Vol. 32, 2003.
6. Kultti, S., Oksanen, P., and Väliranta, M., Holocene tree line, permafrost, and climate dynamics in the Nenets Region, East European Arctic, Canadian Journal of Earth Science, Vol 41, 2004a.
7. V.L. Koshkarova and A.D. Koshkarov, RegionalSignatures of Changing Landscape and Climate of Northern Central Siberia in the Holocene, Russian geology and geophysics, N 6, v. 45, 2004
8. Robert A. Monserud, Nadja M. Tchebakova, and Olga V. Denissenko, Reconstuction of the mid-Holocene Palaeoclimate of Siberia using a bioclimatic vegetation model, Palaeogeography, Palaeoclimatology, Palaeoecology, 139, 1998
9. Ilyashuk, E.A., Ilyashuk, B.P., Andreev, A.A.b, Bennett, K.D., Hammarlund, D., Hubberten, H.W., Chironomid-inferred Holocene mean July air temperatures for the Lena River Delta area, East Siberia, and the Kola Peninsula, northwestern Russia, ACSYS Final Science Conference,11-14 November 2003, Arctic and Antarctic Research Institute (AARI), St. Petersburg, Russia
10. Matul, A. G., et. al., Recent and Late Holocene Environments on the Southeastern Shelf of the Laptev Sea As Inferred from Microfossil Data, Oceanology, Vol. 47, No. 1, 2007.
11. Lawson, D.E.,et. al., 2007, Early to mid-Holocene glacier fluctuations in Glacier Bay, Alaska, in Piatt, J.F., and Gende, S.M., eds., Proceedings of the Fourth Glacier Bay Science Symposium, October 26–28, 2004: U.S. Geological Survey Scientific Investigations Report 2007-5047, p. 54-55.
12. Kaufman, D. S., et. al., Holocene thermal maximum in the western Arctic (0-180°W), Quaternary Science Reviews, 23, 2004
13. Stewart, T. and England, J., Holocene Sea-Ice Variations and Paleoenvironmental Change, Northernmost Ellesmere Island, NWT., Canada, Arctic and Alpine Research, Vol 15, No. 1, 1983.
14. D. Dahl-Jensen, K. Mosegaard, N. Gundestrup, G. D. Clow, S. J. Johnsen, A. W. Hansen, N. Balling, Past Temperatures Directly from the Greenland Ice Sheet, Science, 282, 1998
Climate Optimum (CO), at 8 to 5 ka. Following the CO, temperatures cool to a minimum of 0.5 K colder than the present at around 2 ka. The record implies that the medieval period around 1000 A.D. was 1 K warmer than present in Greenland.” Get copy here