[Kevin09210]

Wait I thought the extreme runaway greenhouse effect had been set aside (read that on here a few years ago IIRC), and it wasn't possible for Earth's atmosphere to turn into Venus'.

Found this from April 2023:

>How a Stable Greenhouse Effect on Earth Is Maintained Under Global Warming

>Plain Language Summary: Observations and model simulations have shown that Earth maintains a stable longwave radiative feedback process. When the surface warms by 1 K, Earth allows for 1.7 to 2.0 Wm−2 of extra thermal cooling to escape to space in cloud-free conditions. Recent studies have claimed that this enhanced thermal cooling to space can be explained by emissions from the surface passing through the atmosphere's infrared window. However, we find that a large portion of the stability actually results from enhanced atmospheric emission during global warming, which arises from the weakening of spectral lines broadening by radiatively inert gases (N2, O2, Ar) as the Earth warms. It is a well-understood phenomenon in spectral physics but has been largely ignored in the feedback literature. As a result, the feedback responses from the thermal radiative effects of greenhouse gases tend to stabilize the climate, rather than initializing a runaway of thermal radiative energy. This study further proposes a simple theory for accurately predicting the clear-sky longwave feedback from climate base states.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2022...

[queuebert]

Thanks for the link -- I hadn't seen that. My issue is that water lost faster than delivered by comets is bad for tectonics, which is bad for atmospheric CO2. They'd have to show no net loss of water, or else the system is not stable over Gyr timescales.