UPDATE: James made this new claim on his weblog titled PM05 resolved (see his comment linked to one of my weblogs in the last paragraph of his post).
The change in heating rate in those plots is much less than 0.05K/day near the surface, probably 0.01K/day (green curve = relevant to the real world). How do you reconcile this with the change in heating rate of about 0.1K PER HOUR that you used in your calculations?
The classic book The Climate Near the Ground by Geiger et al (reprinted most recently in 2009) illustrates the error in James’s statement. On page 124, for example, they report changes of at least 0.1C PER HOUR, and often more, as a result of changes in vertical stratification and surface characteristics. The sensitivity of the 2m temperatures to the overlying thermodynamic stability, intensity of turbulent mixing, and surface fluxes is illustrated even in this early study. The authors discuss atmospheric moisture and cloud cover effects elsewhere in their excellent book. I recommend that James read this text to update himself on the surface boundary layer and for an explanation of the physics of minimum temperatures that occur overnight.
James Annan has posted on his weblog “Pielke and Matsui (2005) revisited”. In it, he perpetuates his misunderstanding of that paper, as well as its role in defining the issue that is examined further in Lin et al 2007 and Klotzbach et al 2009.
His errors start with his text [where he is referring to
Pielke Sr., R.A., and T. Matsui, 2005: Should light wind and windy nights have the same temperature trends at individual levels even if the boundary layer averaged heat content change is the same?Geophys. Res. Letts., 32, No. 21, L21813, 10.1029/2005GL024407]
“In all this work, they apply the radiative cooling at the surface, even though they explicitly portray this forcing as being representative of the effect that arises from a change in GHG concentrations. Standard climate theory holds that the radiative forcing is applied the top of the atmosphere – indeed this is the level at which the forcing is defined. It is simply wrong to claim that a doubling of CO2 will generate a forcing of 3.7Wm-2 at the surface, for example.”
What we actually wrote is
“……if the nocturnal boundary layer heat fluxes change over time, the trends of temperature under light winds in the surface layer will be a function of height, and that the same trends of temperature will not occur in the surface layer on windy and light wind nights.”
The addition of CO2 was presented as just one example of how the nocturnal boundary layer fluxes can change over time. Other examples, include changes in atmospheric water vapor content, cloudiness , and alterations in the surface heat fluxes due to landscape change.
He clearly further illustrates his misunderstanding of this issue as he wrote
“Thus, a large increase in GHGs generates a warming rate of about 0.04K per day across the boundary layer, as compared to the Pielkian ~1K over a single night (depending on wind speed).”
We never stated that there would be a 1K change across the boundary layer. He has completely misrepresented our paper.
The 1K change is concentrated near the surface (e.g. 2m). Figure 1 in
Pielke Sr., R.A., C. Davey, D. Niyogi, S. Fall, J. Steinweg-Woods, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, R. Mahmood, S. Foster, R.T. McNider, and P. Blanken, 2007: Unresolved issues with the assessment of multi-decadal global land surface temperature trends. J. Geophys. Res., 112, D24S08, doi:10.1029/2006JD008229
provides a real world example of how the nocturnal boundary layer cools during the night.
With respect to the actual changes in surface heat fluxes due to a doubling of CO2, this is discussed on my weblog at
Relative Roles of CO2 and Water Vapor in Radiative Forcing).
Further Analysis Of Radiative Forcing By Norm Woods
where the instantaneous simulated flux change from a doubling of CO2 is on the order of 1 Watt per meter squared, as we used in Pielke and Matsui paper. However, it does not matter in our analysis,, what the reason for a change in the cooling rate of 1 Watt per meter squared is.
He also writes
“The startling impact of this odd application of “bottom of the atmosphere” forcing is apparent from their Table 1. A change in this “forcing” of a mere 1Wm-2 leads to a temperature difference of a whopping 1.5C (at the 2m level) over a single calm night! This is the simple result of applying 1Wm-2 of cooling to the fairly shallow layer at the bottom of the atmosphere, which has relatively low heat capacity due to its shallowness.”
He actually recognizes the issue (the cooling effect is concentrated in a fairly shallow layer), but does not see its significance!
The 1.5C temperature difference that he lists results from the manner in which cooling is vertically distributed in the surface boundary layer. With stronger winds, for example, this heating is distributed through a deeper layer.
What we have explored in the Pielke and Matsui (2005), Lin et al (2007) and Klotzbach et al (2009) papers is summarized as follows:
1. A global average surface temperature trend is used to diagnose the magnitude of global warming. This is clearly shown in the equation (from NRC, 2005)
dH/dt = f – T’/λ
where H is the heat content in Joules of the climate system, f is the radiative forcing at the top of the tropopause, T’ is the change in surface temperature in response to a change in heat content, and λ is the climate feedback parameter. Equation (1) above is a thermodynamic proxy for the thermodynamic state of the Earth system; as such, it must be tightly coupled to that
thermodynamic state, as we wrote in our 2007 JGR paper
2. T’ is computed from the equation
T’ = [T' (over the ocean) * area of the ocean + T' (over land) * area of the land]/[area of the Earth's surface].
3. T'(over land) = [T' (maximum) + T' (minimum)]/2
4. T’ is supposed to be monitored at a standard height (e.g. 2m); if it is not, this introduces another bias, but for this discussion, I will assume that all of the land measurements are at 2m.
5. Our papers show that whenever the boundary layer is stably stratified, any alteration in the cooling rate (for any reason), results in a greater temperature change in T’ at 2m than would occur higher up.
6. This means that these values of T’ (from the 2m height) are NOT an appropriate thermodynamic proxy for the thermodynamic state of the Earth system. Values of of temperature anomalies used to calculate T’ when the atmosphere is stably stratified are not tightly coupled to the thermodynamic state of the global climate system.
6. Using observed data from Lin et al 2007, we report (see) that
“[T]he monitoring (and predicting with multi-decadal global models) the temperature at a single level over land near the surface, as representative of deeper layer temperature trends that are positive, introduces a significant warm bias. Until further analysis is completed using temperature trend data at two or more levels near the surface, the best estimate that we have is that this warm bias explains about 30%of the IPCC estimate of global warming [based on a global average surface temperature trend].”
As a final comment, I have worked with James Annan in the past (see). I would be disappointed if he now has decided join the group (such as we see on Real Climate) who inaccurately discuss research papers in order to discredit them.