Scott Denning Admits Climate Alarmism Is Not “Basic Physics”

Denning: The 3.7 W/m2 is from CO2 alone. Without feedbacks this would warm the Earth only 1.1°C (2°F).

The actual climate sensitivity is determined after this initial change (0.27°C per W/m2) gets amplified by positive feedbacks and also reduced by negative feedbacks.

Nelson: How do we know these feedbacks exist?

Denning: We know there must be negative feedbacks because Earth has almost always had liquid water throughout geologic time (oceans never froze solid or boiled away).
We know there must be positive feedbacks because climate has changed in the past even with very small changes to the radiation balance.

Nelson: What are some of the most important feedbacks?

Denning: The most important positive feedbacks are:
Water vapor (warmer oceans increase evaporation, water vapor is a powerful GHG)

Ice and snow albedo (melting snow increases absorption of solar radiation)

High clouds (extra water vapor condenses to make high clouds that let sun in but block outgoing LW (longwave radiation) )

The most important negative feedbacks are:
Increased radiative cooling (Stefan-Boltzmann relationship, OLR = sigma * T^4) Do not worry, you won’t be tested!

Surface warming and extra moisture promote convective clouds that transport heat to upper troposphere where it can be more efficiently radiated to space

Low clouds (extra water vapor condenses to make low clouds that block sun but emit a lot of longwave (Earth) radiation upward because they’re warm — near the ground)

A Global Warming 101 Chat With Climate Scientist Scott Denning | WXshift