Wednesday, October 30, 2013

New paper finds natural variability responsible for abrupt Arctic climate change

Natural variability may have driven Arctic climate change

30.10.2013 19:10

TOP: Map of the Eurasian Arctic (Inset: Severnaya Zemlya (SZ) with the drilling point at Akademii Nauk (AN) ice cap) including schematic positions of Icelandic Low and Siberian High as well as the major air-mass transport pathway (dashed arrow) for SZ. Courtesy: Opel et al. BOTTOM: AN isotope record (including linear trends for 900–1760 and 1800–1998) compared to (from top to bottom) ice cores from Austfonna, Lomonosovfonna and the Vetreniy ice-cap, as well as Arctic summer surface atmosphere temperature (SAT) anomalies, Arctic annual SAT anomalies, AN sodium concentrations, and Arctic sea-ice extent records. Abrupt warming and cooling events exceeding the dominant variability of the AN record are marked by a red asterisk. Note the different scale for the Lomonosovfonna record. Courtesy: Opel et al. Click to enlarge

Strong evidence from ice core oxygen isotope analysis suggests that significant climate change in the Arctic over the last 1,000 years has been due to internal [natural] variability. This may have implications for the suggested causal link between human driven global warming and recent changes in the Arctic, indicating that a far more complex set of relationships are at work; and that significant regional climate change is a feature of the Arctic. 

The paper, Eurasian Arctic Climate Over The Past Millennium As Recorded In The Akademii Nauk Ice Core (Severnaya Zemlya), by Thomas Opel, Hanno Meyer and Diedrich Fritzsche from the Alfred Wegener Institute of the University of Bremen was published this month (October 2013) in the open access journal Climate Of The Past.
The authors examined an ice core from the Russian high Arctic in Severnaya Zemlya. They analysed the levels of the δ18 O isotope of oxygen found at various depth in the ice core. Oxygen isotope analysis of ice core samples can be used as a proxy for temperature, since the mix of isotopes in precipitation depends on the temperature at the time. In general, the further along the length of the ice core that a sample is found then the older it is. So this analysis enables a historic record of surface air temperatures at the ice core site to be estimated.
The authors detected evidence of higher temperatures around 900AD and in the 13th century than were found during the 17th century but they found no evidence of "distinct longer-lasting climate epochs" such as the Medieval Climate Anomaly and the Little Ice Age which have been recorded at lower latitudes.
Instead, the authors report that the oxygen isotope record exhibits "several abrupt cooling and warming events" in the 15th, 16th, 18th and 20th centuries. They suggest that these abrupt changes and the resulting cooling and warming periods may be due to internal climate variability relating to changes in prevailing winds and air-mass transport caused by shifts in atmospheric circulation and also to changes in sea-ice feedbacks in the Barents Sea and Kara Sea.
This also suggests that the Arctic area is subject to significant regional climatic variations which do not necessarily follow the pattern of climate changes at lower latitudes.
The implications of these results is that they suggest that the causes of recent changes in the Arctic may be far more complicated than has previously been believed and that a simplistic attribution to human driven climate change might suggest. 

The conclusion to the paper reads:
The results presented in this paper highlight the potential of the AN (Akademii Nauk) ice core as a high-resolution climate archive for the Late Holocene, i.e. about the last three millennia. Beside a long-term decrease due to climate cooling and ice-cap growth the AN δ18 O record shows evidence of major temperature changes over the last millennium that are representative at least of the western Eurasian Arctic, i.e. the Barents and Kara seas region. Of particular importance are several abrupt cooling and warming events leading e.g. to the absolute SAT (surface air temperature) minimum around 1800 and the absolute SAT maximum in the early 20th century, accompanied by significant changes in sodium concentrations. The ETCW (early twentieth century warming) exhibits a specific double-peaked shape typical of the Barents and Kara seas region. Abrupt changes in the last centuries might be caused by internal [natural] climate dynamics related to shifts of atmospheric circulation patterns and corresponding sea-ice feedbacks

The abstract reads:
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.

Eurasian Arctic Climate Over The Past Millennium As Recorded In The Akademii Nauk Ice Core (Severnaya Zemlya)
by T.Opel, D. Fritzsche and H. Meyer
doi: 10.5194/cp-2379-2013 Clim.Past. 9-2379-2389, 2013
Read the paper here.


  1. Fig 5 in this paper shows Arctic temps in 1930's-1940's were higher than at end of record in 2000