Periodic Reporting for period 3 - Couplet (Transient climate change in the coupled atmosphere--ocean system)
Período documentado: 2021-10-01 hasta 2023-03-31
The hypothesis of this project is that the variations of the climate sensitivity parameter reflect inadequacies in scientific understanding of the global energy balance, in particular its neglect of geographical patterns of temperature change. The objective of the project is to develop a new framework for describing the variations of the coupled atmosphere--ocean climate system, taking into account the influences on and the effects of the geographical patterns, and to apply this framework to the analysis of historical and simulated climate change, in order to set refined constraints on the processes, pattern and magnitude of future climate change.
* We have demonstrated that the climate sensitivity parameter varied over the last 100 years by a factor of two on multidecadal timescales both in reality and in climate model simulations, but the models are quite unrealistic in the timing of the variation. In the models, sensitivity reached its maximum in recent decades, whereas in same period it was at its minimum in the real world, due to an unusual pattern of temperature trends in the Pacific Ocean.
* We have found that this pattern is likely to have been produced in reality by a delayed response to explosive volcanic eruptions. This pattern of response is largely absent in the models.
* We have examined how the climate sensitivity parameter increases as time passes under constant elevated CO2 because of the way in which the pattern of surface temperature change evolves, and shown that it is greater for higher CO2 concentration.
* We have proposed a refined model of the role of climate feedback in the global energy balance, in which the climate sensitivity parameter depends on the change in the vertical profile of atmospheric temperature. This dependence accounts for the effect of the geographical pattern of SST change.
* Through comparative analysis of results from a set of model experiments with increasing CO2, we have found conceptual deficiencies in the paradigm which has been commonly used in the last decade for understanding the role of ocean heat uptake in the global energy balance, and we suggest an improved interpretation.