This experiment was performed at the Hadley Centre during 1995 and 1996 using the Second Version of the UK Met. Office's Unified Model (HadCM2), consisting of an 19-layer high resolution atmospheric GCM, coupled to a 20-layer ocean model. The horizontal resolution of the atmospheric and ocean models was 2.5deg. latitude by 3.75deg. longitude.
The greenhouse gas only integrations (which are used in SCENGEN) used the combined forcing of all the greenhouse gases as an equivalent CO2 concentration. These greenhouse gas integrations simulated the change in forcing of the climate system by greenhouse gases since the early industrial period (taken to be 1860), thus being 'warm-start' simulations. This experiment consisted of four separate simulations using the HadCM2 model with identical forcing but with different initial conditions, a so-called ensemble experiment. The historic forcing for each simulation being introduced at 150-year intervals in the long control integration. The scenario forcing was introduced in 1990, and consisted of a 1% per annum increase in equivalent CO2 concentration through to 2100. The first ensemble member of the experiment is reported in Kattenburg et al. (1996) and Mitchell and Johns (1997), while the full ensemble of four simulations is reported in Mitchell et al. (1999). The ensemble-mean response is used in SCENGEN Version 2.4 (earlier versions of SCENGEN used the first member only).
We acquired the results from this experiment in 1996 and 1997 through the Climate Impacts LINK Project, based in the Climatic Research Unit. The greenhouse gas only change fields used in SCENGEN are calculated as the difference in climate between the 30-year means of years 2071-2100 and 1961-90 in the greenhouse gas only forced simulation. The global warming by 2071-2100, with respect to 1961-90, averaged 3.1deg C in the four-member ensemble and the increase in global precipitation was 5.01%, yielding a global precipitation sensitivity of 1.6% per degree Celsius warming. The climate sensitivity of the same atmospheric model, coupled to a mixed-layer ocean, was estimated to be 2.5deg C.
Mean monthly precipitation pattern correlation coefficient = 0.76
Mitchell,J.F.B., Johns,T.C., Eagles,M., Ingram,W.J. and Davis,R.A. (1999) Towards the construction of climate change scenarios Climatic Change, 41, 547-581.
Mitchell,J.F.B. and Johns,T.C. (1997) On the modification of global warming by sulphate aerosols J.Climate, 10, 245-267.