Historical Simulations With HadGEM3‐GC3.1 for CMIP6

Abstract

We 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.Plain Language Summary Historical simulations, which successfully reproduce features of the observed climate from the end of the preindustrial period to the near-present day, contribute to our understanding of the underlying mechanisms that drive or influence climate variability and climate change. The historical simulations described in this paper use the third Hadley Centre Global Environment Model in the Global Coupled configuration 3.1 model. These simulations form part of the UK's contribution to the sixth Coupled Model Intercomparison Project. We assess various aspects of the historical climate system in our simulations against observations. 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. The key findings include (a) that the model global mean surface temperature broadly follows the observed record, with a few quantitative differences, and (b) that the ocean circulation and sea surface temperatures of the North Atlantic are likely influenced by historical forcings. In general, the simulations respond to historically evolving influences in a similar manner to the observed world. Therefore, these simulations contribute, as part of the wider CMIP6 multimodel effort, to the understanding of the causes of observed climate change since 1850.

The Evaluation of the North Atlantic Climate System in UKESM1 Historical Simulations for CMIP6

“…It is also interesting to note that these low-frequency changes in the AMOC are similar to those seen in AOD ( Figure 9) and N d (Figure 12), albeit with a lag. Therefore, the changes in AMOC are consistent with the aerosol forcing (Menary et al, 2013(Menary et al, , 2020 and are also consistent with the forced AMOC changes in GC3.1 (Andrews et al, 2020). However, we note that the rising AMOC is also accompanied by some multidecadal variability about the long-term AMOC trend with similar time scales to AMV (Figure 16a).…”

“…Therefore, these biases suggest that the ocean stratification may be too weak. • Over the twentieth century, UKESM1 simulates significant multidecadal variability in basin mean SST, which is similar to the observed AMV ( Figure 16), and the variability simulated in GC3.1 (Andrews et al, 2020). This variability is consistent with a forced response due to changes in anthropogenic aerosols (Booth et al, 2012).…”

“…Many aspects of the North Atlantic climate system have been evaluated extensively in the latest UK physical climate model, HadGEM3‐GC3.1 (Andrews et al., 2020; Kuhlbrodt et al., 2018; Menary et al., 2018; Mulcahy et al., 2018; Williams et al., 2018). Therefore, here we focus our analysis exclusively on UKESM1 and compare with the published examples in those papers.…”

Description and evaluation of aerosol in UKESM1 and HadGEM3-GC3.1 CMIP6 historical simulations

“…All forcings and how they are implemented in both models are described fully in (Sellar et al, 2019b). The GC3.1 historical simualations are evaluated in full in Andrews et al (2019). For CMIP6 a total of 19 and 4 ensemble members were run for UKESM1 and GC3.1 respectively.…”

Uncertainty in Aerosol Radiative Forcing Impacts the Simulated Global Monsoon in the 20th Century

“…The SMURPHS dataset consists of historical climate simulations run over the period 1850-2014 using a fully coupled version 5 of HadGEM3-GC3.1 at resolutions of N96 and 1° in the atmosphere and ocean respectively (Kuhlbrodt et al, 2018;Williams et al, 2018). The model version used here is a development version towards the UK submission to CMIP6 (Andrews et al, 2020;Dittus et al, 2020;Hardiman et al, 2019). HadGEM3 uses the GLOMAP two-moment aerosol scheme that includes representations of the cloud albedo and cloud lifetime effects (Mulcahy et al, 2018 and references therein).…”