Abstract
Rapid adjustments are responses to forcing agents that cause a perturbation to the top of atmosphere energy budget but are uncoupled to changes in surface warming. Different mechanisms are responsible for these adjustments for a variety of climate drivers. These remain to be quantified in detail. It is shown that rapid adjustments reduce the effective radiative forcing (ERF) of black carbon by half of the instantaneous forcing, but for CO2 forcing, rapid adjustments increase ERF. Competing tropospheric adjustments for CO2 forcing are individually significant but sum to zero, such that the ERF equals the stratospherically adjusted radiative forcing, but this is not true for other forcing agents. Additional experiments of increase in the solar constant and increase in CH4 are used to show that a key factor of the rapid adjustment for an individual climate driver is changes in temperature in the upper troposphere and lower stratosphere.
Highlights
Owing to its expected better correspondence to equilibrium surface temperature change, effective radiative forcing (ERF) has taken precedence over the older definition of stratospherically adjusted radiative forcing (RF) for measuring perturbations to the Earth’s radiative energy budget (Boucher et al, 2013; Forster et al, 2016; Myhre et al, 2013; Shine et al, 2003)
Rapid adjustments are usually considered to be part of the forcing (Forster et al, 2013; Gregory et al, 2004). It has long been known (Manabe & Wetherald, 1975) that an increase in CO2 concentrations cools the stratosphere, which reduces longwave (LW) outgoing radiation, increasing the positive forcing compared to the instantaneous radiative forcing (IRF) of CO2
We find this to be true as interkernel agreement is good except for stratospheric temperature adjustment to 2xCO2 forcing as discussed below
Summary
Owing to its expected better correspondence to equilibrium surface temperature change, effective radiative forcing (ERF) has taken precedence over the older definition of stratospherically adjusted radiative forcing (RF) for measuring perturbations to the Earth’s radiative energy budget (Boucher et al, 2013; Forster et al, 2016; Myhre et al, 2013; Shine et al, 2003). Rapid adjustments are usually considered to be part of the forcing (Forster et al, 2013; Gregory et al, 2004) It has long been known (Manabe & Wetherald, 1975) that an increase in CO2 concentrations cools the stratosphere, which reduces longwave (LW) outgoing radiation, increasing the positive forcing compared to the instantaneous radiative forcing (IRF) of CO2 (the convention in this paper is to report IRF at the TOA). Such knowledge is incorporated into the definition of RF. These components all induce their own responses in the TOA energy balance, which are not included in the standard RF framework
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