# Extreme sensitivity and climate tipping points

## TL;DR

This paper investigates how climate tipping points lead to extreme values in equilibrium climate sensitivity, contrasting linear and nonlinear measures, and confirms findings across models.

## Contribution

It introduces a comparison between linearized and nonlinear ECS notions, highlighting the impact of tipping points on climate sensitivity extremes.

## Key findings

- Tipping points cause extremes in both ECS measures.
- Multiple regimes with different sensitivities are identified.
- Results are confirmed in a physics-based climate model.

## Abstract

A climate state close to a tipping point will have a degenerate linear response to perturbations, which can be associated with extreme values of the equilibrium climate sensitivity (ECS). In this paper we contrast linearized (`instantaneous') with fully nonlinear geometric (`two-point') notions of ECS, in both presence and absence of tipping points. For a stochastic energy balance model of the global mean surface temperature with two stable regimes, we confirm that tipping events cause the appearance of extremes in both notions of ECS. Moreover, multiple regimes with different mean sensitivities are visible in the two-point ECS. We confirm some of our findings in a physics-based multi-box model of the climate system.