Australia: The Land Where Time Began

A biography of the Australian continent 

Greenland Temperature Anomalies - Origin of Multidecadal to Centennial Scales Over the Last 800 Years

When assessing the impact of climate change on human societies the surface temperature of the Greenland Ice Sheet is among the most important of the climate variables through its association with the level of the oceans. As a consequence of the relatively short period over which sea level records have been kept the causes of Greenland temperature changes on a decadal to centennial scale are not well understood. In order to study these the authors1 calculated the Greenland temperature anomalies GTA[G-NH] for the past 800 years, subtracting the standardised northern hemisphere (NH) from the standardised Greenland standardised temperature. The result was the Greenland temperature variation being decomposed into background climate (NH); polar amplification: and regional variability (GTA[G-NH] ). The central Greenland polar amplification factor, expressed by the variance ratio Greenland/NH is 2.6 for the time interval of the past 161years, and 3.3-4.2 over the past 800 years. 31-35 % of the Greenland variation of temperature in the multidecadal-centennial time scales for the past 800 years is explained by the  GTA[G-NH]. The authors1 found that solar-induced atmospheric circulation pattern changes, such as those produced by the North Atlantic Oscillation/Arctic Oscillation (NAO/AO), have influenced the  GTA[G-NH]. The anomaly is also likely to be linked to the solar-paced changes in the Atlantic Meridional Overturning Circulation (AMOC), as well as changes in the associated northwards oceanic heat transport, as indicated by evidence from climate modelling and proxy temperature records.

Authors'1 conclusions

Background changes of climate at the Northern Hemisphere scale has dominated the Greenland temperature over the past 800 years, and it is known that these changes largely result from solar and volcanic forcing before 1850 (Crowley, 2000). They found that atmospheric dynamics, such as those produced by the NAO/AO, in which longer-term variations are induced by responses of the atmospheric circulation to solar output variations, with the oceanic response also contributing, also strongly influence the Greenland temperature deviations from those of the Northern Hemisphere. It is indicated by this finding that over the past 800 years the Greenland temperature minimum occurred in the early 18th century, though the Northern Hemisphere minimum occurred in the 15th - 16th century, probably as a result of an increase in solar forcing in the 18th century. Also, the Greenland temperature exhibited warming in the latter part of the 20th century, at a time of high solar activity, that was less pronounced than that of the Northern Hemisphere. The authors1 suggest that if solar activity in the future is low compared to that of the past 100 years (Livingston & Penn, 2009), hidden Greenland warming may be revealed that is due to increasing levels of atmospheric greenhouse gases that were emitted in the latter half of the 20th century.

 

Sources & Further reading

  1. Kobashi, T., Shindell, D. T., Kodera, K., Box, J. E., Nakaegawa, T., and Kawamura, K.: On the origin of multidecadal to centennial Greenland temperature anomalies over the past 800 yr, Clim. Past, 9, 583-596, doi:10.5194/cp-9-583-2013, 2013.  
Author: M. H. Monroe
Email: admin@austhrutime.com
Last updated: 20/04/2013
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading