You are on the same order of magnitude as CO2
without water vapor feedback.
In other words, if I increase substance X by 1 % in the atmosphere, what is the effective change in radiative forcing (or temperature), either with or
without water vapor feedbacks?
Not exact matches
First, for changing just CO2 forcing (or CH4, etc, or for a non-GHE forcing, such as a change in incident solar radiation, volcanic aerosols, etc.), there will be other GHE radiative «forcings» (
feedbacks, though in the context of measuring their radiative effect, they can be described as having radiative forcings of x W / m2 per change in surface T), such as
water vapor feedback, LW cloud
feedback, and also, because GHE depends on the vertical temperature distribution, the lapse rate
feedback (this generally refers to the tropospheric lapse rate, though changes in the position of the tropopause and changes in the stratospheric temperature could also be considered lapse - rate
feedbacks for forcing at TOA; forcing at the tropopause with stratospheric adjustment takes some of that into account; sensitivity to forcing at the tropopause with stratospheric adjustment will generally be different from sensitivity to forcing
without stratospheric adjustment and both will generally be different from forcing at TOA before stratospheric adjustment; forcing at TOA after stratospehric adjustment is identical to forcing at the tropopause after stratospheric adjustment).
The 0.9 degr.C for 2xCO2 is from the Modtran program, carefully composed from laboratory measurements, where line by line absorption characteristics were measured and implemented for different air pressures (heights),
water, CO2 and CH4 levels, for different parts of the globe and with or
without clouds, rain,... That is a basic «model»,
without any real life
feedbacks (except
water vapor, which may be included in different ways).
Without a strong positive
feedback from
water vapor (as assumed in the models), Human - made climate forcing becomes insignificant.
One can't arbitrarily choose
feedbacks for
water vapor, ice / albedo, clouds, etc.,
without looking to see how these phenomena are actually behaving — e.g., what are the radiative properties of
water vapor, how is relative humidity changing, what is happening to low cloud cover, high cloud cover, and the high / low cloud ratios, etc.?.
You figure out how that tiny
water vapor feedback can help CO2 do something to the climate
without models yet??
The direct CO2 radiative forcing is the change in infrared radiative fluxes for a doubling CO2 (typically from 287 to 574 ppm),
without any
feedback processes (e.g. from changing atmospheric
water vapor amount or cloud characteristics.)