The discussion centers on Earth's longwave energy imbalance, particularly focusing on observational data regarding changes since 2000. Participants explore the implications of absorbed solar radiation (ASR) and outgoing longwave radiation (OLR) in relation to greenhouse gas effects and feedback mechanisms within the climate system.
Participants express differing views on the mechanisms of feedback and the implications of OLR changes, indicating that the discussion remains unresolved with multiple competing perspectives on the energy imbalance and greenhouse gas effects.
There are limitations regarding the assumptions made about feedback mechanisms and the dependence on definitions of forcing and feedback within the climate system. The discussion does not resolve these complexities.
Added greenhouse gases are supposed to be decreasing the OLR.Satellite observations from the Clouds and the Earth’s Radiant Energy System show that Earth’s energy imbalance has doubled from 0.5 ± 0.2 Wm−2 during the first 10 years of this century to 1.0 ± 0.2 Wm−2 during the past decade. The increase is the result of a 0.9 ± 0.3 Wm−2 increase absorbed solar radiation (ASR) that is partially offset by a 0.4 ± 0.25 Wm−2 increase in outgoing longwave radiation (OLR).
From the data it is difficult to see if any positive forcing happened at all, in the longwave spectrum. Without the initial perturbation, there would not be anything to feedback upon.olivermsun said:Say a “unit” of greenhouse gas forcing temporarily decreases OLR and causes temperatures to rise. Eventually OLR has to catch up and counteract the earlier imbalance; else the system would keep warming indefinitely.
In the real climate system, there are additional positive feedbacks that amplify the “original” radiative imbalance, and hence the OLR has to make up for them as well. That’s why the OLR at later times is not just the same as original but actually larger even though the original forcing initially caused a decrease in OLR.