Unprecedented Recent Ice Cap Retreat in Arctic Canada
Abstract
The instrumental record of global mean annual surface air temperature (SAT) shows warming from ~1970 to 2010 of ~0.7 °C, while estimates of coeval trends in the Arctic are 3 to 4 times larger, reflecting the strong positive feedbacks unique to polar regions. However, the degree of "Arctic Amplification" and the extent to which recent Arctic warming is anomalous with respect to natural climate variability remain difficult to evaluate because of the limited temporal and spatial coverage of the instrumental record within the Arctic and the presence of multi-decadal temperature trends that may be related to internal modes of climate system variability. Placing the recent warming in a longer perspective requires secure reconstructions of past summer temperatures. Cold-based ice caps preserve evidence that places recent summer warming in a millennial perspective. Ice caps overlying relatively flat terrain remain frozen to their bed and may act as preservation agents, entombing the landscape present when the ice cap formed. The mass balance of ice caps in the Canadian Arctic is dominated by summer temperature; as summer temperatures have risen, ice caps have been receding, revealing their preserved ancient landscapes. Radiocarbon dates on rooted plants revealed as ice margins recede document the last time each site was ice free. We have determined the radiocarbon ages on 147 samples of rooted tundra vegetation collected the year of their exposure by ice recession over a 1000 km transect in the Eastern Canadian Arctic. The dates demonstrate that average summer temperatures of the most recent decades have been higher than any half-century in at least 37,000 years, and likely since the Last Interglaciation ~130,000 to 120,000 years ago. This includes the peak warmth of the early Holocene, when solar energy in summer was 9% greater than at present, providing compelling evidence that recent anthropogenic contributions to the atmosphere have now resulted in summer warming well outside the range of natural climate variability.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.C43E..08M
- Keywords:
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- 0720 CRYOSPHERE / Glaciers;
- 0762 CRYOSPHERE / Mass balance;
- 1616 GLOBAL CHANGE / Climate variability;
- 1621 GLOBAL CHANGE / Cryospheric change