Considerations of Earth climate sensitivity based on peculiarities of planetary heat capacity using system identification method: Runaway greenhouse effect scenario is still possible

TL;DR

This paper uses system identification to evaluate Earth's climate sensitivity, revealing a range of 2-7°C and highlighting the potential for a runaway greenhouse effect due to positive feedback mechanisms.

Contribution

It introduces a novel application of system identification to estimate climate sensitivity and assesses the impact of feedbacks on runaway greenhouse scenarios.

Findings

Earth's equilibrium climate sensitivity is between 2°C and 7°C.

Positive feedback from CO2 increases the risk of runaway greenhouse effect.

The feedback coefficients from water vapor, methane, and albedo could be less than 1.

Abstract

System identification method (SIM) was used to evaluate the Earth equilibrium climate sensitivity. According to our simulations, the equilibrium climate sensitivity was found to be between 2 deg C and 7 deg C. Analysis of the changes in heat inventory of oceans, atmosphere, land, and cryosphere was based on the experimental data of IPCC6. The equation derived for Earth's global surface temperature (GST) shows that the sum of the dimensionless feedback coefficients from water vapor, methane, and Earth albedo could be less than 1. However, due to the positive feedback from carbon dioxide (the combined greenhouse catastrophe) and the revised equilibrium climate sensitivity estimate based on an increase in equilibrium climate sensitivity, the probability of the runaway greenhouse effect increases significantly. It is still less than the critical number when not considering the feedback associated with carbon dioxide, water vapor, and methane buildup in Earth's atmosphere. The analysis considers the thermal dynamics of the oceans and other factors, including the exponential growth of the Earth's global temperature based on IPCC6 data.