Abstract
AbstractWe describe and evaluate historical simulations which use the third Hadley Centre Global Environment Model in the Global Coupled configuration 3.1 (HadGEM3‐GC3.1) and which form part of the UK's contribution to the sixth Coupled Model Intercomparison Project, CMIP6. These simulations, run at two resolutions, respond to historically evolving forcings such as greenhouse gases, aerosols, solar irradiance, volcanic aerosols, land use, and ozone concentrations. We assess the response of the simulations to these historical forcings and compare against the observational record. This includes the evolution of global mean surface temperature, ocean heat content, sea ice extent, ice sheet mass balance, permafrost extent, snow cover, North Atlantic sea surface temperature and circulation, and decadal precipitation. We find that the simulated time evolution of global mean surface temperature broadly follows the observed record but with important quantitative differences which we find are most likely attributable to strong effective radiative forcing from anthropogenic aerosols and a weak pattern of sea surface temperature response in the low to middle latitudes to volcanic eruptions. We also find evidence that anthropogenic aerosol forcings play a role in driving the Atlantic Multidecadal Variability and the Atlantic Meridional Overturning Circulation, which are key features of the North Atlantic ocean. Overall, the model historical simulations show many features in common with the observed record over the period 1850–2014 and so provide a basis for future in‐depth study of recent climate change.
Highlights
This paper describes and evaluates the historical simulations which form part of the UK's contribution to the sixth Coupled Model Intercomparison Project (CMIP6 Eyring et al, 2016), organized under the auspices of the World Climate Research Programme's Working Group on Coupled Modeling
We find that the simulated time evolution of global mean surface temperature broadly follows the observed record but with important quantitative differences which we find are most likely attributable to strong effective radiative forcing from anthropogenic aerosols and a weak pattern of sea surface temperature response in the low to middle latitudes to volcanic eruptions
We decided to minimize the chance of experiments starting from similar oceanic states by considering the two leading modes of multidecadal sea surface temperature (SST) variability, the Interdecadal Pacific Oscillation (IPO; Power et al, 1999; Zhang et al, 1997) and the Atlantic Multidecadal Oscillation (AMO; Kerr, 2000), which naturally arise in the piControl runs (Menary et al, 2018)
Summary
This paper describes and evaluates the historical simulations which form part of the UK's contribution to the sixth Coupled Model Intercomparison Project (CMIP6 Eyring et al, 2016), organized under the auspices of the World Climate Research Programme's Working Group on Coupled Modeling. The historical period (1850–2014), from approximately the end of the industrial revolution through to the near-present day, represents a time span over which the anthropogenic influence on greenhouse gases, aerosols, and land use has increased This period includes a number of major tropical volcanic eruptions and solar variability, which can have a climatic influence on annual-to-decadal timescales. The observational record provides evidence of the combined impact of natural and anthropogenic forcings, the caveats being that these records are often short and globally incomplete and that they include the stochastic influence of internal variability of the climate system Despite these limitations, the approach adopted in this paper is to benchmark the historical experiments against the observational record to ascertain whether the simulations can recreate observed phenomena. These historical simulations provide initial conditions for CMIP6 “future” scenario simulations, having been “spun-up” with 165 years of time-varying historical forcings
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