The Impact of Time Varying Feedbacks on Global and Regional Scale Temperature Projections

Abstract:

During the historical period, the rate of global mean surface warming and the energy imbalance at the top of atmosphere have been shown to be influenced by time varying spatial patterns of warming. This “pattern effect” could exert a strong influence on future surface warming in the coming decades, but the implications for projections are under explored. In this study, we use a simple two-layer energy balance model (EBM) to explore temperature projections accounting for plausible time variations in the climate feedback parameter from the pattern effect. We separate the impact of pattern effects driven by forced responses from those driven by internal variability. The EBM allows for both fast and slow responses to climate forcing and for the efficacy of deep ocean heat uptake and is calibrated to emulate complex climate models from the Coupled Model Intercomparison Project Phase 6. We have further developed the EBM to project regional scale temperature responses over a near-term, policy relevant, time scale. We find that global and regional scale temperature changes over the period to 2050 are highly sensitive to changes in the feedback parameter from the pattern effect, demonstrating the need to account for this mechanism in projections.