Geoscience Reference
In-Depth Information
18. Equilibrium climate sensitivity
(4) Climate models fail to reconstruct or predict natural variability.
The global climate system contains cyclic variations, which occur on a decade or sub-dec-
ade timescale. The most famous is El Niño, which is a change in both ocean and atmo-
spheric circulation in the Pacific region occurring every three to seven years that has a
major influence on the rest of the global climate. Sceptics argue that climate models have
been unable to simulate satisfactorily these events in the past. However, climate models
have become better at reconstructing these past variations in El Niño-Southern Oscillation
(ENSO), North Atlantic Oscillation (NAO), and related Arctic Oscillation (AO) as there
has been an increasing realization that these have a profound impact upon regional climate
(see
Climate: A Very Short Introduction
). Most models are able to depict these natural
variations, picking out particularly the 1976 climate shift that occurred in the Pacific
Ocean. All the AOGCMs have predicted outcomes for ENSO and NAO for the next 100
years. However, a lot of improvement is required before there will be confidence in the
model predictions. It is, though, testament to the realism of the AOGCMs that they can in-
deed reconstruct and predict future trends in these short-term oscillations.
