Prospects for narrowing bounds on Earth's equilibrium climate sensitivity

Abstract

The concept of Earth's Equilibrium Climate Sensitivity (ECS) is reviewed. A particular problem in quantifying plausible bounds for ECS has been how to account for all of the diverse lines of relevant scientific evidence. It is argued that developing and refuting physical storylines (hypotheses) for values outside any proposed range has the potential to better constrain these bounds and to help articulate the science needed to narrow the range further. A careful reassessment of all important lines of evidence supporting these storylines, their limitations, and the assumptions required to combine them is therefore required urgently.

Observational Constraints on Cloud Feedbacks: The Role of Active Satellite Sensors

“…However, in the most recent report of the IPCC, the ECS is still judged to be ''likely in the range 1.5-4.5°C'' (IPCC 2013), illustrating that the uncertainties in ECS have proven to be remarkably resilient. Much progress has been made, however, in the identification and understanding of the processes that control climate sensitivity (Stevens et al 2016a). A reduction in the range of ECSparticularly at the high end where the risks are greatest and the economic benefits of better information are largest-would be tremendously valuable in improving our abilities to better plan for climate change (Cooke et al 2013;Neubersch et al 2014) and would help determine the levels of greenhouse gas emissions compatible with a global warming target of 1.5 or 2°C.…”

Objectively combining AR5 instrumental period and paleoclimate climate sensitivity evidence

“…It may be possible better to constrain ECS by combining probabilistic evidence from different sources. Several authors have sought to do so (Hegerl et al 2006;Annan and Hargreaves 2006;Aldrin et al 2012;Stevens et al 2016) using subjective Bayesian methods, however their results were significantly influenced by Abstract Combining instrumental period evidence regarding equilibrium climate sensitivity with largely independent paleoclimate proxy evidence should enable a more constrained sensitivity estimate to be obtained. Previous, subjective Bayesian approaches involved selection of a prior probability distribution reflecting the investigators' beliefs about climate sensitivity.…”

FAIR v1.1: A simple emissions-based impulse response and carbon cycle model

“…While we cannot absolutely , but probably more so) to balance. Progress towards tightening these upper bounds could therefore be achieved with a better understanding of the present-day aerosol forcing (Stevens et al, 2016).…”