CONSTRAIN’s new Knowledge Gains: Summary and Implication Report (KGSIR) details the latest scientific knowledge on Effective Radiative Forcing or ERF.
This is the first in a series of reports covering scientific advances on topics ranging from rapid adjustments and climate sensitivity to carbon budgets and climate projections. Each report will outline key findings from the CONSTRAIN project and their implications for climate science.
Effective radiative forcing (ERF) is the change in the Earth’s energy balance when a forcing agent, such as greenhouse gases or aerosol emissions, are introduced into the system. Positive radiative forcing means the Earth gains heat and the climate warms, whilst negative forcing has a cooling effect.
There are different aspects to radiative forcing: instantaneous radiative forcing (IRF) is the sudden change in energy balance when forcing agents are introduced. The forcing agents can meanwhile also cause changes to the atmosphere itself, called rapid adjustments, which can either increase or reduce the overall radiative forcing.
ERF is a combination of IRF and rapid adjustments, so it includes the initial change in the climate system as well as the rapid changes occurring in the atmosphere, reflecting the overall change in surface temperature caused by the different forcing agents.
There are uncertainties in ERF for both aerosols and greenhouse gases. Aerosol concentrations vary over space and time, and their behaviour in the atmosphere is not yet fully understood. More is known about how greenhouse gases behave, but there are complexities when it comes to computer modelling as well as the effects of rapid adjustments.
The CONSTRAIN project is investigating these processes and their uncertainties, and using them to provide more robust methods for calculating ERF that can be applied to a large range of forcing agents. This better understanding of ERF will improve our knowledge of how different forcing agents contribute to climate change, feeding into global climate models and assessments.
We will provide further updates on ERF as the project progresses.
(a) Effective Radiative Forcing (W m-2) due to a doubling of CO2 concentration; (b) Efficacy of a range of climate drivers