Modelling Maastrichtian climate: investigating the role of geography, atmospheric CO2 and vegetation
Other literature type
Hunter, S. J.
Valdes, P. J.
Haywood, A. M.
Markwick, P. J.
(issn: 1814-9332, eissn: 1814-9332)
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 CO<sub>2</sub> 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×CO<sub>2</sub> Maastrichtian conditions and a further
3.9°C warming associated with a quadrupling of atmospheric
CO<sub>2</sub> 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 CO<sub>2</sub>
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.