atmosphere

“In the context of climate change, external factors that can lead to warming are typically called forcings. This would be things like changes to the solar flux, volcanic eruptions, and our release of greenhouse gases into the atmosphere. Feedbacks are then responses to this externally driven warming that either act to amplify, or suppress, the warming. Some of these are fast, such as water vapour and clouds, while others are slower, such as changes to vegetation or ice sheets. Some are also negative and quite strong (such as the Planck response). This means that even though the overall effect of these feedbacks is to amplify the externally-driven warming, it is limited (the negative feedbacks eventually balance the the effect of the change in forcing and the resulting positive feedbacks). For example, if we were to double atmospheric CO2, we’d expect to eventually warm by about 3oC.

A runaway, on the other hand, typically refers to what happened on Venus. Essentially, virtually all of the CO2 was released into the atmosphere, the warming was so substantial that any liquid water evaporated and was eventually lost to space, most atmospheric molecules lighter than CO2 were also lost to space, and the surface warmed by many 100s of oC. On the Earth, such a runaway is simply not possible, because most of the carbon, that can then form CO2, is locked up in the lithosphere. We can’t emit enough CO2, either through anthropogenic influences or naturally, to undergo a runaway.”

A few comments.
“This would be things like changes to the solar flux,”
This happens on a simple yearly basis due to the elliptical orbit
volcanic eruptions,
Clouds deserve a mention. Both reduce the flux.
“and our release of greenhouse gases into the atmosphere”
The crux of the matter and also any concerns re possible runaway climates.

“A runaway, on the other hand, typically refers to what happened on Venus”
A description often mooted but not strictly correct on 2 grounds.
Venus’ atmosphere and temperature is due to its size, composition and distance from the sun [orbit]
No runaway involved.
Second the runaway scenario involves an unrealistic approach to the actual scientific effects that can happen.
“Feedbacks generally cannot be negatively greater than the initiating force” Lucia.
Now I understand that some things appear to.
Super balls would be a good example.
The atmospheric temperature and surface temperature of the Earth and Venus.
The problem with free energy problems is that they cannot actually exist.
If the earth, atmosphere or not, continued to grab and build up energy from the sun, not releasing all of it back to space. It would eventually become hotter than the sun but unable to radiate this heat.
Runaway models and ideas are based on this unrealistic approach.

Note nowhere is this a denial of atmospheres heating up in response to GHG. Just the misapplication of the idea of retained heat constantly building up forever.