Quantifying zonal patterns of climate feedbacks and their role in polar amplification

The significant climate warming seen over the 20th century has been largely attributed to anthropogenic emissions of greenhouse gases. Spatial patterns of likely future warming are dependent on patterns of climate feedback, but current understanding of climate feedbacks is largely at the global mean or hemispheric scale. The aim of this project is to improve understanding of zonal mean climate feedbacks and their contribution to polar amplification using observations and models.

Zonal mean climate feedbacks and contributions to the equilibrium temperature response were determined for eight slab ocean GCMs forced by doubling CO2 and for a single model under different forcing mechanisms. Relative contributions to polar amplification and the greatest inter-model differences in zonal mean feedbacks and temperature response contributions are presented.

Contributions to the temperature response of AOGCM simulations of the 20th century due to radiative forcing, climate feedback and heat storage/transport were analyzed to understand how well climate models reproduce the observed 20th century temperature record. They generally perform well despite large differences in feedback strength through compensating differences in forcing and heat storage/transport, but projected future warming trends are much more dependent on a model’s feedback strength. The poor representation of tropical 20th century warming and Arctic amplification in some models are attributed to unrealistic forcing or feedback patterns. Over the whole of the 20th century, the feedback strength is likely to be underestimated by the multi-model mean.

Zonal patterns of surface albedo feedback were determined from AOGCMs and satellite observations in the seasonal cycle and long term climate change contexts. Observations show large changes in long term albedo feedback in regions outside the cryosphere, unlike models. Land use change or vegetation feedbacks and difficulties of measuring albedo under different cloud conditions may be to blame. The observed annual mean NH mid to high latitude feedback is greater than that for models. Models and observations agree in some regions in their seasonal cycle feedback but different satellite data sets show some significant differences.