Modelling Maastrichtian climate: investigating the role of geography, atmospheric CO2 and vegetation
1British Antarctic Survey, NERC, High Cross, Madingley Road, Cambridge, CB3 OET, UK
2BRIDGE, School of Geographical Sciences, University Road, Bristol, BS8 1SS, UK
3School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
4GETECH, Kitson House, Elmete Hall, Elmete Lane, Leeds, LS8 2LJ, UK
Abstract. In this paper we describe the results from an ensemble of palaeoclimate simulations of the Maastrichtian using the fully-coupled dynamic ocean-atmosphere General Circulation Model, HadCM3L. Using appropriate Maastrichtian boundary conditions, we investigate the sensitivity of the predicted palaeoclimate to changing atmospheric CO2 levels and modelled vegetation treatment. In addition, we explore the climatic response to the changed geography using a comparison with a pre-industrial experiment. We describe our results alongside the findings of previous modelling studies in particular with consideration to concepts of climate equability. Our findings demonstrate increased global temperatures compared with the pre-industrial experiment, with a 5.9°C increase in temperatures associated with the change to 1×CO2 Maastrichtian conditions and a further 3.9°C warming associated with a quadrupling of atmospheric CO2 levels. Compared to the pre-industrial we find a latitudinal temperature profile that is reduced in gradient and shifted to higher temperatures. Our control 4×CO Maastrichtian experiment exceeds the pre-industrial by 6.5–8.6°C, 7.4–11.2°C, and 10.1–32.4°C in the equatorial, mid and high latitudes respectively. We also find a general pattern of increased thermal seasonality in the high latitudes. In terms of global mean annual temperatures we find a range of 18.1–23.6°C for our 1–6×atmospheric CO2 envelope. Other than in the northern high latitudes we find satisfactory levels of agreement between the ensemble temperature envelope and estimates from palaeotemperature proxies. The inclusion of a dynamic vegetation model (TRIFFID) leads to a further increase in the thermal seasonality at high latitudes, warming in the mid to high latitudes and increased precipitation in the low and mid latitudes.