Atmospheric excitation of length of day inferred from 21st century climate model projections

The Coupled Model Intercomparison Project Phase 6 (CMIP6) provides, amongst others, the Earth climate response to several different scenarios that simulate possible future anthropogenic drivers of climate change. The scenarios are characterized by different forcings, which are defined from a combination of plausible future societal developments, the Shared Socioeconomic Pathways (SSPs), and the Representative Concentration Pathways (RCPs), identified by the approximate radiative forcing level anticipated for 2100.

In a previous work, we investigated length of day variations induced by multi-model projections of zonal wind fields, stemming from historical simulations and from the four scenarios SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5. In order to cover the same set of five scenarios that are treated in the sixth assessment report of the Intergovernmental Panel on Climate Change, we add another low emission scenario, SSP1-1.9, in this follow-up study. Furthermore, we do not only assess the wind term but complete the analysis with the calculation of the respective atmospheric surface pressure terms. We are especially interested in the long-term variations and trends of length of day predicted for the period from 2015-2100 and the connection with variations and trends of the global surface temperature patterns. Regarding the excitation by zonal winds, preliminary assessments show that higher emission scenarios, which are associated with more intense global warming, would lead to a moderate increase in atmospheric angular momentum and thus to a proportional decrease of the Earth rotation rate.