Can we use linear response theory to assess geoengineering strategies?

Geoengineering can control only some climatic variables but not others, resulting in side-effects. We investigate in an intermediate-complexity climate model the applicability of linear response theory (LRT) to the assessment of a geoengineering method. This application of LRT is twofold.

Fluctuation analysis of the atmospheric energy cycle.

The atmosphere gains available potential energy by solar radiation and dissipates kinetic energy mainly in the atmospheric boundary layer. We analyze the fluctuations of the global mean energy cycle defined by Lorenz in a simulation with a simplified hydrostatic model. The energy current densities are well approximated by the generalized Gumbel distribution and the Generalized Extreme Value (GEV) distribution.

Coherence resonance in an atmospheric global circulation model.

Numerical evidence is presented of a coherence-resonant behavior, induced on an atmospheric global circulation model by a white (in time and space) additive Gaussian noise with amplitude A << 1 . Intermediate A values enhance the spatiotemporal regularity of vortical patterns that contribute to the intra-annual variability of the atmospheric component of the climate. Only weak patterns (those appearing in the summer hemisphere) become ordered by noise.

Synchronization experiments with an atmospheric global circulation model.

Synchronization in a chaotic system with many degrees of freedom is investigated by coupling two identical global atmospheric circulation models. Starting from different initial conditions, the two submodels show complete synchronization as well as noncomplete synchronization depending on the coupling strength. The relatively low value of the coupling strength threshold for complete synchronization indicates the potential importance of synchronization mechanisms involved in climate variability.