Publication Date:
2013-02-20
Description:
Comparison of simulated and reconstructed past climate variability within the last millennium provides an opportunity to aid the understanding and interpretation of palaeoclimate proxy data and to test hypotheses regarding external forcings, feedback mechanisms and internal climate variability under conditions close to those of the present day. Most such comparisons have been made at the Northern Hemispheric scale, of which a selection of recent results is briefly discussed here. Uncertainties in climate and forcing reconstructions, along with the simplified representations of the true climate system represented by climate models, limit our possibility to draw certain conclusions regarding the nature of forced and unforced climate variability. Additionally, hemispheric-scale temperature variations have been comparatively small, wherefore the last millennium is apparently not a particularly useful period for estimating climate sensitivity. Nevertheless, several investigators have concluded that Northern Hemispheric-scale decadal-mean temperatures in the last millennium show a significant influence from natural external forcing, where volcanic forcing is significantly detectable while solar forcing is less robustly detected. The amplitude of centennial-scale variations in solar forcing has been a subject for much debate, but current understanding of solar physics implies that these variations have been small – similar in magnitude to those within recent sunspot cycles – and thus they have not been a main driver of climate in the last millennium. This interpretation is supported by various comparisons between forced climate model simulations and temperature proxy data. Anthropogenic greenhouse gas and aerosol forcing has been detected by the end of Northern Hemispheric temperature reconstructions. Keywords: Palaeoclimate, climate proxy data, climate models, climate forcings, external climate variability, internal climate variability, Northern Hemisphere, temperature, last millennium (Published: 19 February 2013) Citation: Tellus B 2013, 65 , 19921, http://dx.doi.org/10.3402/tellusb.v65i0.19921 This publication is part of a Thematic Cluster with papers presented at a conference held in Stockholm 21 - 23 May 2012, to honor the late Professor Bert Bolin for his outstanding contributions to climate science and his efforts to create a dialogue between policy makers and the scientific community. All papers within the cluster will be published online as soon as they have been accepted for publication. When all papers belonging to the cluster have been published, they will be summarized with a foreword describing the background and scope of the conference.
Print ISSN:
0280-6509
Electronic ISSN:
1600-0889
Topics:
Geography
,
Physics
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