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Yet Another Hockey Stick

Temperatures of North Atlantic “are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming” — Science « Climate Progress.png

Joe Romm:

Temperatures of North Atlantic “are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming” : Study after study finds recent warming is unprecedented in magnitude and speed and cause.  The anti-science crowd keeps trying to debunk one or two old Hockey Sticks, but new ones crop up faster than a speeding puck. Science just published a new one, “Enhanced Modern Heat Transfer to the Arctic by Warm Atlantic Water” (subs. req’d), news release here, “Warming North Atlantic water tied to heating Arctic, according to new study.” I have pulled out the key graph — and it is one heck of a Hockey Stick.... derived from “planktic foraminifers in a sediment core.... This astonishing warming in the past century is clearly not, as the anti-science crowd likes to say, some sort of recovery from the so-called Little Ice Age (see “A detailed look at the Little Ice Age“), which, in any case, is barely noticeable in this data.   The lead author, Robert Spielhagen of the Leibniz Institute of Marine Sciences said, “Such a warming of the Atlantic water in the Fram Strait is significantly different from all climate variations in the last 2,000 years.”  The fact is, over 90% of human-caused warming is going into the oceans — and it is melting ice whereever it goes (see “Deep ocean heat is rapidly melting Antarctic ice“).

Air temperatures in Greenland have risen roughly 7 degrees F in the past several decades, thought to be due primarily to an increase in Earth’s greenhouse gases, according to CU-Boulder scientists. “We must assume that the accelerated decrease of the Arctic sea ice cover and the warming of the ocean and atmosphere of the Arctic measured in recent decades are in part related to an increased heat transfer from the Atlantic,” said Spielhagen.

Here are the abstract and conclusion:

The Arctic is responding more rapidly to global warming than most other areas on our planet. Northward-flowing Atlantic Water [AW] is the major means of heat advection toward the Arctic and strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ~150 years. Here, we present a multidecadal-scale record of ocean temperature variations during the past 2000 years, derived from marine sediments off Western Svalbard (79°N). We find that early–21st-century temperatures of Atlantic Water entering the Arctic Ocean are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming….

Although we cannot quantify from our data the variability of previous AW inflow to the Arctic by volume, our temperature data series and the above observational link suggest that the modern warm AW inflow (averaged over two to three decades) is anomalous and unique in the past 2000 years and not just the latest in a series of natural multidecadal oscillations. Both effects—a temperature rise as well as a volume transport increase—introduce a larger heat input into the Arctic Ocean. Although there is no direct contact of the AAWL [Arctic Atlantic Water Layer] with the ocean surface in the Arctic, such an increased heat input has far-reaching consequences. The strong AW warming event in the Arctic Ocean in the 1990s caused a shoaling of the AW core and an enhanced heat flux to the surface , concurrent with decreasing sea ice. Recent oceanographic data from the Laptev Sea continental margin indicate the impact of warm AW-related water masses on the shallow (<50 m) shelf, a feature not observed before in a >80-year time series. The data also provide evidence for a significant heat flux to the overlying shelf waters. Even without any modification of the vertical heat transfer processes, the enhanced temperature contrast between the AW and the surface sea water freezing point (increased from ~5 to 7 K as identified here) leads to an increase in the vertical heat flux of ~40%. Any positive-feedback mechanism will magnify the effect of this flux increase on the ice cover. Complementing the strong feedback between ice and atmospheric temperatures, warming of the AW layer, unprecedented in the past 2000 years, is most likely another key element in the transition toward a future ice-free Arctic Ocean.