Wednesday, Oct 15, 2008
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.
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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.
This article was posted: Wednesday, October 15, 2008 at 4:00 am