A “simulation” of Mid‐Cretaceous climate

Abstract

A series of general circulation model experiments utilizing GENESIS have been completed for the mid‐Cretaceous based on geography, variable atmospheric carbon dioxide concentrations (2 to 6 times present‐day concentrations), and variable poleward oceanic heat flux (.6 to 1.2 × 1015 W increased from present day). By combining all three major variables (CO2, geography, and oceanic heat flux), the distribution of mid‐Cretaceous temperatures can be achieved. In the simulations, increased CO2 is required to promote global warmth, and increased oceanic heat flux is required to prevent the tropics from overheating with higher levels of CO2. Four times present‐day CO2 with 1.2 × 1015 W provided the best match to the distribution of mid‐Cretaceous data. The best match to the Cretaceous observations was achieved with a globally averaged surface temperature increase of 6.2°C, at the lower end of past estimates of mid‐Cretaceous warmth. This value may be a better estimate of mid‐Cretaceous global warming. Finally, the model experiments can be used to provide a “paleocalibration” of the global warming expected for a doubling of atmospheric carbon dioxide. The best estimates for the mid‐Cretaceous appear to be a 2.5 to 4.0°C sensitivity, in the mid to upper range of the sensitivity of current climate models used to assess future global change.

Modeling the influence of a reduced equator-to-pole sea surface temperature gradient on the distribution of water isotopes in the Early/Middle Eocene

“…As observed before (e.g. Barron et al, 1995;Sloan et al, 2001), imposed warm high latitude SSTs have little impact on extratropical continental interior temperatures. Simulated continental interior cold month temperatures in EO-AZOLLA (not shown) are colder than indicated by proxy data (Basinger, 1991;Markwick, 1994;Sloan, 1994;Wolfe, 1994;Greenwood and Wing, 1995).…”

Precipitation rates and atmospheric heat transport during the Cenomanian greenhouse warming in North America: Estimates from a stable isotope mass-balance model

“…Quantifying global transfers of sensible heat by the oceans (Covey and Barron, 1988;Crowley, 1991;Barron et al, 1995;Sloan et al, 1995) and latent heat by the atmosphere are necessary to explain warmer polar temperatures (Parrish and Spicer, 1988a, b) during greenhouse periods of Earth history (Schneider et al, 1985;Huber et al, 1995;Upchurch et al, 1999). Increased global temperatures increase the saturation vapor pressure of the troposphere, and modify latent heat transfer from low to high latitudes .…”

Deep water formation and poleward ocean heat transport in the warm climate extreme of the Cretaceous (80 Ma)

“…Late Cretaceous atmospheric CO2 was much higher than today, with levels estimated from 2 to 9 times present day [Berner, 1990]. Earlier Atmospheric General Circulation Model (AGCM) simulations of Cretaceous climate showed higher CO2 was needed to warm the poles sufficiently and larger poleward heat transport in the one layer 'slab' ocean model was required to maintain a reduced equator to pole surface temperature gradient consistent with marine and continental fossil and isotopic evidence [Barron et al, 1995]. Although larger slab ocean heat transport produces reduced surface temperature gradients in AGCMs, it is difficult to understand how larger ocean heat transport can occur in a Cretaceous ocean with reduced thermal gradients.…”