2004 LOM Workshop

Tuesday 11:50 a.m. - 12:10 p.m.

The influence of internal variability on climate projections

Helge Drange, Asgeir Sorteberg, Nils Gunnar Kvamsto, Tore Furevik
Nansen Environmental and Remote Sensing Center
helge@nersc.no

ABSTRACT

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With identical greenhouse forcing climate models shows a wide range of responses both globally and regionally. This divergence from a single solution may be partly due to different model formulations and partly due to unpredictability of the climate system due to internal variability within the climate system itself. The contribution to the total model spread from each of the two uncertainties is complex and dependent on type of climate variable, the strength of the greenhouse forcing as well as the spatial and temporal scales that are investigated. In order to estimate the contribution of the spread due to internal variability an ensemble of simulations using one coupled climate model is performed. Thus the influence of intermodel differences on the spread is cancelled and it is possible to make an estimate of the influence of internal variability on the climate projections. The ensemble was carried out with the coupled Bergen Climate Model (BCM) using the atmospheric model ARPEGE with a resolution of T63 and 31 levels in the vertical and the ocean model MICOM with a resolution of 2.4 degrees along the equator and 24 vertical levels. The ensemble members have all been integrated with a 1% increase per year in CO2 content for 80 years, but started in different initial ocean and atmosphere states (taken from a control run). Our findings suggest that climate change projections over a period of less than 40-50 years will be strongly influenced by chaotic (or unpredictable) internal climate variability. Thus multi-model spread on these time-scales may partly be influenced by real model differences and partly by internal chaotic variations.

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LOM Users' Workshop, February 9-11, 2004