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Cold conditions in the Gulf of St. Lawrence

16 Nov 2022 | Science Notes

If you’re going to Anticosti Island, perched in the St Lawrence where the giant river meets the Atlantic ocean, take your boots because the ground is boggy. And take your coat because it’s cold. Indeed if you’re thinking it seems colder than it used to be, you’re right, in a long term way, because those peat bogs have now been studied and, based on the way the rate at which the peat accumulates is sensitive to local temperature and precipitation, they show that the climate of that part of Eastern Canada was warmer in the summer than it is now for most of the past 8,000 years. The layers in those bogs tell a story that looks nothing like the usual hockey stick history.

The study, led by scientists from the Université du Québec à Montréal, involved finding two peatland bogs with the right kinds of peat and the right amount of exposure to the maritime climate to allow the scientists to reveal climate conditions through the distant past by examining the types and amounts of peat that accumulated annually layer-by-layer in core samples from underground.

The temperature history they reconstructed looks like this:

The chart is from their paper. But the horizontal yellow line was added by Kenneth Richard of NoTricksZone, who spotted the paper, and shows the study authors’ estimate of the present day mean July temperature (15 degrees C).

As these things often do, the chart reads from left to right with 0 being no years BP (Before Present). So the leftmost actual data point is 150 years ago, and as you go to the right you go farther back in history with the number of years shown on the horizontal axis.

The sharp decline in temperature 600 years ago corresponds with the Little Ice Age. Prior to that was the Medieval Warm period. Prior to that was... basically a lot of warm conditions relative to the present-day average, back to about 5,000 years ago, and then prior to 7,000 years ago. And notice also that the yellow line representing current temperatures is well below the point where that data line stops a century and a half ago.

If the reconstruction is right, Anticosti has cooled over the past 150 years, back to some of the lowest temperatures over the past 8,000 years. But even if it had merely stayed constant rather than cooling, there would still be no denying that the message in the peat bog shows a lot of natural variability, no hockey stick, and nothing unusual about current temperatures in that part of eastern North America.

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