Quantifying the effects on the Earth System of Palaeogeographic uncertainties during the Miocene

Abstract

It has long been realised that palaeogeographic differences between the palaeo and modern and CO2 concentrations are essential in driving the climates in Earth’s history. Many palaeoclimate modelling studies, especially DeepMIP, have primarily focussed on the sensitivity to CO2 with the modelling protocol requiring groups to run multiple CO2 sensitivity simulations while sensitivity to palaeogeography was considered an optional extra, with only one low resolution alternative provided. Yet there are considerable uncertainties in plaeogeography, even for the Cenozoic. Thus, there is a need to better quantify the climate uncertainty caused by palaeogeographic uncertainty. We used 4 alternative palaeogeographies with several CO2 levels, and investigated the differing climate and ocean carbon cycle responses. The results of this study highlight the significance of palaeogeography in driving climates of the Earth System during a key time period of the past. Regionally, the palaeogeographic uncertainties drive a climate and ocean biogeochemistry response that can
exceed that driven by CO2 alone. Even at the global scale, the differences can be similar to CO2 forcing. The research shows there is an urgent need to review existing palaeogeography reconstructions and apply new methodologies for palaeoaltitude reconstructions for key mountain belts (e.g., the Rocky Mountains, the Tibetan Plateau). The research has also shown that care must be applied to the inferences from palaeo model intercomparison projects that do not encompass palaeogeographic uncertainty. It is possible that models may be deemed to be “right/wrong” for the wrong reasons depending on the confidence in the palaeogeographic reconstructions. Of course, in practice all of our results are based on one climate model, and it would be important to confirm these analysis with other climate models. Finally, we note that the Miocene is a relatively geologically recent period and uncertainties in palaeogeography, and corresponding climate, will likely grow larger for older time periods. It
is therefore essential that palaeo climate models should be more frequently evaluated using multiple palaeogeographies.

Date of Award	17 Jun 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Paul J Valdes (Supervisor) & Alexander J Farnsworth (Supervisor)