The Flux-Anomaly-Forced Model Intercomparison Project (FAFMIP) contribution to CMIP6: investigation of sea-level and ocean climate change in response to CO<sub>2</sub> forcing

Abstract

Abstract. The Flux-Anomaly-Forced Model Intercomparison Project (FAFMIP) aims to investigate the spread in simulations of sea-level and ocean climate change in response to CO 2 forcing by atmosphere-ocean general circulation models (AOGCMs). It is particularly motivated by the uncertainties in projections of ocean heat uptake, global-mean sealevel rise due to thermal expansion and the geographical patterns of sea-level change due to ocean density and circulation change. FAFMIP has three tier-1 experiments, in which prescribed surface flux perturbations of momentum, heat and freshwater respectively are applied to the ocean in separate AOGCM simulations. All other conditions are as in the pre-industrial control. The prescribed fields are typical of pattern and magnitude of changes in these fluxes projected by AOGCMs for doubled CO 2 concentration. Five groups have tested the experimental design with existing AOGCMs. Their results show diversity in the pattern and magnitude of changes, with some common qualitative features. Heat and water flux perturbation cause the dipole in sea-level change in the North Atlantic, while momentum and heat flux perturbation cause the gradient across the Antarctic Circumpolar Current. The Atlantic meridional overturning circulation (AMOC) declines in response to the heat flux perturbation, and there is a strong positive feedback on this effect due to the consequent cooling of sea-surface temperature in the North Atlantic, which enhances the local heat input to the ocean. The momentum and water flux perturbations do not substantially affect the AMOC. Heat is taken up largely as a passive tracer in the Southern Ocean, which is the region of greatest heat input, while the weakening of the AMOC causes redistribution of heat towards lower latitudes. Future analysis of these and other phenomena with the wider range of CMIP6 FAFMIP AOGCMs will benefit from new diagnostics of temperature and salinity tendencies, which will enable investigation of the model spread in behaviour in terms of physical processes as formulated in the models.

Response of the North Atlantic dynamic sea level and circulation to Greenland meltwater and climate change in an eddy-permitting ocean model

“…6a, b), leads to positive SSH anomalies north of the GS and in the Labrador Sea (indicating a weakening of the North Atlantic subpolar gyre discussed in the next section) and to negative SSH anomalies in the subtropical North Atlantic, Irminger Sea and Nordic Seas (relative to the global-mean). This is in general agreement with sea level projections based on climate change scenarios (e.g., Suzuki et al 2005;Landerer et al 2007;Yin et al 2010), including with the CMIP5 model-mean SSH change (Bouttes et al 2014;Gregory et al 2016). The drop of the mean SSH in the Nordic Seas, simulated under the warmer climate conditions (Fig.…”

“…5a, b; see also Saenko et al 2015). In addition, the warming causes large positive heat flux anomalies in the Labrador Sea, consistent with the CMIP5 model-mean heat flux change (Bouttes et al 2014;Gregory et al 2016), and negative heat flux anomalies in the GS separation region (Fig. 5a, b).…”

“…In climate projections for the twenty first century, changes of the SSH typically have complex geographical patterns (e.g., Suzuki et al 2005;Landerer et al 2007;Yin et al 2010;Bouttes et al 2014;Gregory et al 2016), with the standard deviation being particularly large in the North Atlantic (Gregory et al 2016). This, along with interannual climate variability, can attenuate the link between changes in the AMOC rate and SSH field in such simulations (e.g., Landerer et al 2007).…”

The PMIP4 contribution to CMIP6 – Part 3: The last millennium, scientific objective, and experimental design for the PMIP4 <i>past1000</i> simulations

“…PMIP will provide input to and benefit from diagnostic projects performed within the framework of the Ocean Model Intercomparison Project (OMIP, Griffies et al, 2016) and its biogeochemical component (OCMIP, Orr et al, 2016), the Sea-Ice MIP (SIMIP, Notz et al, 2016), the Fluxanomaly-forced MIP (FAFMIP, Gregory et al, 2016), and the Coupled Climate -Carbon Cycle MIP (C4MIP, Jones et al, 2016).…”

Interdisciplinary knowledge exchange across scales in a globally changing marine environment

“…Generally, scientists working on decision support favour parsimonious model designs that are easy to communicate with stakeholders, have relatively short computational times that allow for quick scenario testing to be conducted and can incorporate multiple data sources such as expert elicitation and quantitative data (Hay, Morrow, Kopp, & Mitrovica, 2015). For example, tools developed to map the implications of climate change induced sea level rise typically use estimates developed without considering thermal expansion as the parameter uncertainty associated with more complex representations does not materially aid the decisionmaking process and the simpler representation provides adequate information for informed climate change policies and governance (Dutton et al, 2015;Gregory et al, 2016). Yet thermal expansion is one of the two most important sources of sea level rise and essential for predicting accurate global sea level rise (Church et al, 2001).…”