One also needs to clearly distinguish between radiative forcing (the total change in the rate of radiative cooling to space since pre-industrial assuming no warming) and the radiative imbalance. If you imaging an instantaneous doubling of CO2, the radiative forcing and radiative imbalance will both be about 3.6 W/m2, but as the planet warms, the radiative forcing will be unchanged while the radiative imbalance will gradually shrink to zero as a new steady state is approached. In the real world, radiative forcing has been rising gradually and the radiative imbalance is always less than the forcing because forcing has already produced some warming.

Let’s suppose the climate feedback parameter is 2 W/m2/K. In that case, the roughly 1 K of warming we have experienced would be associated with a increase emission or reflection (OLR+OSR) of 2 W/m2. Radiative forcing is currently at about 2.7 W/m2, meaning that about 70% of forcing would have been counterbalanced by increased OLR+OSR, while 0.7 W/m2 is still going into warming the planet, mostly the ocean (ARGO). This is why energy balance models say ECS is about 1.8 K/doubling

Expressed mathematically:

RF = CFP*dT + OHU

At any time during forced warming, the radiative forcing (RF) is going into warming the planet, mostly the ocean (OHU), and being lost by increased radiative cooling to space. When ocean heat uptake becomes negligible, warming has resulting in a new steady state where dT = RF/CFP.

]]>“If you perform radiative transfer calculation for instantaneously doubling CO2, there is approximately a 3.5 W/m2 decrease in LWR leaving the TOA”

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When one actually looks at the change in OLR over the last 33 years one finds an _increase_ in LWR leaving earth. Not a _decrease_

I have no doubt that this real world fact will leave modellers entirely unfazed. You lot will just brush it off as a “contrarian myth”, or some such.

Dewitte & Clerbaux; Remote Sensing 2018, 10, 1539; doi:10.3390/rs10101539

]]>One can divide climate change into three categories: “anthropogenically forced” variability, “naturally forced” variability (volcanos and sun), and “unforced” or “internal” variability. The historical record of temperature variation during the Holocene provides evidence about the sum of naturally-forced and unforced variability, and solar and volcanic proxies provide some ability to separate naturally-forced variability from unforced variability – though it still isn’t clear to me if unforced variability played an important role in the LIA. My qualitative understanding (I haven’t seen a good quantitative record) is that the nearly 1 K of warming over the last 50 years is unusual in light of the Holocene, especially given that it followed the warming that ended the LIA.

On the other hand, some of the warming from 1920-1945 and the cooling that followed (both about 0.2 K clearly appears to be unforced. The red line on the linked graph is AR5 best estimate of forcing vs time. (Figure 8-18).

]]>I agree with SoD that “Climate models are the best tools we have for estimating the future climate state,” and also that few on the blogs and in the media have any idea what they’re talking about. Also with John that “Well yes, the internet generates mostly rubbish from people of all persuasions including some climate scientists.”

Several above say they’re OK with 40 year trends. Same here, but we’re assuming that natural variability these past 40 years is something like zero or very little variability. Maybe. Actual climate sensitivity may be much higher or lower than the recent, mostly 1.5- 2.0 estimates, depending on the unknown of natural variability. Here we have, unfortunately, another likeness to social science, the inability to know certainly, and yes, the inability to know probabilistically.

All of this makes climate science and energy policy the wicked problems most of us admit it is. How do we convey the complexity to those who want simplistic, binary answers to the problem and to the solutions.

Perhaps machine learning would be more accurate. ]]>

IF I understand correctly, M&W were also the first to fully describe radiative-convective equilibrium in the atmosphere and possibly recognize radiative imbalances at the TOA were critical. Before then, a surface energy balance perspective dominated.

]]>One can look at the response to doubling CO2 from a TOA energy balance perspective (+3.5 W/m2 less heat escaping) or a surface energy balance perspective (+1 W/m2 more heat arriving).

From the TOA perspective, the planet looks like a graybody with a surface temperature of 288 and an emissivity of 0.61. Planck feedback for such an object is -3.3 W/m2/K. So slightly more than a 1 K increase in surface temperature (with no feedbacks) can restore radiative balance after a doubling of CO2.

From the surface energy balance perspective, the planet is nearly a blackbody at 288 K. Planck feedback for such an object is -5.4 W/m2/K, meaning it only takes a 0.2 K rise in surface temperature to restore radiative balance in response to a 1 W/m2 increase in DLR. That is the 0.17 W/m2 dTs in Figure 4. Somewhere Ramanathan has figured that the warmer atmosphere is going to radiate an addition 2 W/m2 to the surface, meaning 0.5 K of warming is needed without feedbacks.

In either case, the climate feedback parameter is critical, the additional amount of heat emitted or reflect to space per degK of surface warming (W/m2/K). And the increase in upward heat transfer per degK of surface warming must be the same at all altitudes as it is at the TOA (where only radiation is involved). However, while one can calculate changes in radiation with temperature from first principles, convection is more challenging. That is what Ramanathan is trying to do in this paper. (Table 3).

For example, if one assumes that the flux of latent heat from the surface rises as fast as saturation vapor pressure (7%/K), then just the increased latent heat leaving the surface is 5.6 W/m2/K, far too big if feedback is positive. I haven’t check out his rational for all of the values in Table 3.

Hope this helps.

]]>I do think there is information on aerosols in the temperature record. Fitting the past 40-years independently of the pre-1970 periods is one way to access this information.

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