A model intercomparison of changes in the Atlantic thermohaline circulation in response to increasing atmospheric CO₂ concentration

Abstract

[1] As part of the Coupled Model Intercomparison Project, integrations with a common design have been undertaken with eleven different climate models to compare the response of the Atlantic thermohaline circulation (THC) to time-dependent climate change caused by increasing atmospheric CO 2 concentration. Over 140 years, during which the CO 2 concentration quadruples, the circulation strength declines gradually in all models, by between 10 and 50%. No model shows a rapid or complete collapse, despite the fairly rapid increase and high final concentration of CO 2 . The models having the strongest overturning in the control climate tend to show the largest THC reductions. In all models, the THC weakening is caused more by changes in surface heat flux than by changes in surface water flux. No model shows a cooling anywhere, because the greenhouse warming is dominant. Citation: Gregory, J. M., et al. (2005), A model intercomparison of changes in the Atlantic thermohaline circulation in response to increasing atmospheric CO 2 concentration, Geophys. Res. Lett., 32, L12703,

Long-term ice sheet–climate interactions under anthropogenic greenhouse forcing simulated with a complex Earth System Model

“…Relating the reduction to the strength of the mean overturning as is done in Fig. 3 of Gregory et al (2005), our model shows a relative reduction in overturning compared to its mean strength which is slightly weaker than suggested by the mean regression line in this figure, which has a slope of -0.45 ± 0.14 (y against x).…”

“…The mean reduction of the maximum of the NAMOC is (averaged over the 20 years prior to reaching the final pCO 2 level) 7 Sv (individual values between 6 and 8 Sv), which is equivalent to a 26% reduction. The reductions in the models analysed in Gregory et al (2005) vary between 10 and 50%. Relating the reduction to the strength of the mean overturning as is done in Fig.…”

“…The first is a simulation with a prescribed exponential increase in atmospheric CO 2 concentration until 49 the pre-industrial concentration is reached after 140 years. The detailed setup as well as the results from the participating coupled climate models is presented in Gregory et al (2005). We use the first 140 years of our 49_1w and 49 experiments.…”

Presentation, calibration and validation of the low-order, DCESS Earth System Model (Version 1)

“…This approach serves to keep down the degrees of freedom in our low-order model but at the expense of being able to deal with climate change associated with simulated changes in ocean circulation. Most coupled climate models exhibit weakened meridional overturning circulations for global warming (Gregory et al, 2005). On the other hand, reconstructions of past conditions show weaker overturning for cooler conditions and data from high-resolution climate archives like ice cores indicate that there is considerably more climate variability due to ocean circulation changes when climate is colder than during warmer interglacial periods (Toggweiler and Russell, 2008;Grootes and Stuiver, 1997).…”

Synoptically forced hydroclimatology of major Arctic watersheds in general circulation models; Part 2: Eurasian watersheds

“…E-mail: jfinnis@eos.ubc.ca . ocean circulation and global climate (Broecker, 1997;Gregory et al, 2005;Bindoff et al, 2007). On a regional scale, changes in Eurasian flow conditions can affect the formation and break-up of sea ice along the Eurasian coast, influencing the exchange of heat and moisture between the ocean and the atmosphere (Frey et al, 2003;Ye et al, 2003) Arctic hydrology is expected to have a pronounced response to climate change, which can exert an influence through a variety of mechanisms.…”