UCL Discovery
UCL home » Library Services » Electronic resources » UCL Discovery

Modelling the long-term carbon cycle, atmospheric CO2, and Earth surface temperature from late Neoproterozoic to present day

Mills, BJW; Krause, AJ; Scotese, CR; Hill, DJ; Shields, GA; Lenton, TM; (2019) Modelling the long-term carbon cycle, atmospheric CO2, and Earth surface temperature from late Neoproterozoic to present day. Gondwana Research , 67 pp. 172-186. 10.1016/j.gr.2018.12.001. Green open access

[thumbnail of 1-s2.0-S1342937X18302818-main.pdf]
Preview
Text
1-s2.0-S1342937X18302818-main.pdf - Published version

Download (2MB) | Preview

Abstract

Over geological timescales, CO2 levels are determined by the operation of the long term carbon cycle, and it is generally thought that changes in atmospheric CO2 concentration have controlled variations in Earth's surface temperature over the Phanerozoic Eon. Here we compile independent estimates for global average surface temperature and atmospheric CO2 concentration, and compare these to the predictions of box models of the long term carbon cycle COPSE and GEOCARBSULF. We find a strong relationship between CO2 forcing and temperature from the proxy data, for times where data is available, and we find that current published models reproduce many aspects of CO2 change, but compare poorly to temperature estimates. Models are then modified in line with recent advances in understanding the tectonic controls on carbon cycle source and sink processes, with these changes constrained by modelling 87Sr/86Sr ratios. We estimate CO2 degassing rates from the lengths of subduction zones and rifts, add differential effects of erosion rates on the weathering of silicates and carbonates, and revise the relationship between global average temperature changes and the temperature change in key weathering zones. Under these modifications, models produce combined records of CO2 and temperature change that are reasonably in line with geological and geochemical proxies (e.g. central model predictions are within the proxy windows for N~75% of the time covered by data). However, whilst broad long-term changes are reconstructed, the models still do not adequately predict the timing of glacial periods. We show that the 87Sr/86Sr record is largely influenced by the weathering contributions of different lithologies, and is strongly controlled by erosion rates, rather than being a good indicator of overall silicate chemical weathering rates. We also confirm that a combination of increasing erosion rates and decreasing degassing rates over the Neogene can cause the observed cooling and Sr isotope changes without requiring an overall increase in silicate weathering rates. On the question of a source or sink dominated carbon cycle, we find that neither alone can adequately reconstruct the combination of CO2, temperature and strontium isotope dynamics over Phanerozoic time, necessitating a combination of changes to sources and sinks. Further progress in this field relies on N108 year dynamic spatial reconstructions of ancient tectonics, paleogeography and hydrology. Whilst this is a significant challenge, the latest reconstruction techniques, proxy records and modelling advances make this an achievable target.

Type: Article
Title: Modelling the long-term carbon cycle, atmospheric CO2, and Earth surface temperature from late Neoproterozoic to present day
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.gr.2018.12.001
Publisher version: https://doi.org/10.1016/j.gr.2018.12.001
Language: English
Additional information: This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
Keywords: Carbon cycle, Modelling, Paleoclimate, Biogeochemistry, Tectonics
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10089966
Downloads since deposit
68Downloads
Download activity - last month
Download activity - last 12 months
Downloads by country - last 12 months

Archive Staff Only

View Item View Item