Climate Models
CMIP6 ECS
3 hours ago
By Rud Istvan
This post was motivated by May’s second here on paleoclimate, by comments to Bradley Jr’s climate models repost from AIER, and my previous posts and comments about climate models and equivalent (observational) or equilibrium (modeled) climate sensitivity (aka ECS). All are hyperlinked below. This post summarizes some of the most important climate basics at a simple high level, while pulling together the myriad underlying specifics via linked references to a lot of stuff posted at WUWT over the years. Hopefully this is helpful at both levels for the many newer WUWT commenters. It also indirectly takes scientific aim at some of the extreme skeptics who also comment here, like those who deny that the greenhouse effect exists, or that ECS cannot be significantly positive.
First, the green house effect (GHE) is real although often misunderstood. Unlike a real greenhouse (which works by inhibiting surface convective cooling), the GHE works by inhibiting radiative cooling in the troposphere. “Greenhouse” gases (GHG) absorb and omni-directionally re-emit infrared radiation (IR), inhibiting (retarding) cooling IR escape to space. Greenhouse gasses (so also their ‘back radiation’) cannot warm—incoming insolation is solely responsible for that. But as first shown experimentally by Tyndall in 1859, GHG can inhibit radiative cooling. The level in the troposphere where the GHE ceases to be a factor is called the effective radiating level (ERL). The ERL is also why the GHE can never saturate. More GHG just raises ERL, meaning the ERL emission temperature is cooler so less efficient thanks to the troposphere temperature lapse rate. Which is why Guy Callendar realized in his 1938 paper that increasing CO2 has a decreasing logarithmic effect. For what follows, that also means that whatever the ECS per CO2 doubling might be, it remains about constant over a much broader concentration range.
https://wattsupwiththat.com/2021/06/25/cmip6-ecs/
