Earth system responses to positive, net-zero and negative CO2 emissions: Findings from the TerraFIRMA idealised overshoot experiments

Speaker:  Colin Jones

Chair(S): Oscar martinez-alvarado

wednesday march 26 2025, 13:00

ABSTRACT

I present some first results from the TerraFIRMA idealized overshoot experiment protocol, which is now the international TIPMIP Earth system model (ESM) experiment protocol. The protocol applies positive, zero, and negative CO2 emissions (only) to ESMs in order to control the rate of global warming (under positive emissions) across participating ESMs.

Long-term, zero-emission runs branch off the (warming) positive emission runs at common levels of global warming across models. At a common timepoint into the zero emission runs, negative CO2-emission simulations are branched that cause the ESMs to cool back to pre-industrial temperatures. This idealized protocol ensures a common global warming, climate stabilization, global cooling pathway across all participating models, allowing us to construct different global warming overshoot and stabilization pathways. Using these pathways we are investigating the behaviour and reversibility of the coupled climate system and carbon cycle, studying the long-term response of the Earth system to net-zero CO2 emissions, and assessing the risks and potential consequences of key Earth system tipping points being exceeded. I will outline the experiment protocol and show a number of results following this protocol with the UKESM model.

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