Response to CCSP Comment on the Pielke and Matsui GRL paper

The CCSP Response to the Public Comments includes a comment on the Pielke and Matsui 2005 paper entitled “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?”.

There has already been an informative exchange on this topic in William M. Connolley’s weblog STOAT.

The importance of this paper, and the identification of a warm bias in the surface temperature trend assessments, were summarized in the Climate Science weblog of January 23 2006.

This weblog dissects their reply in segements. The CCSP Response (page 140) stated,

1. ‘Since 1979, Tmin has not warmed relative to Tmax globally; see Vose et al Geophysical Research Letters, 32, doi:10.1029/2005GL024379(2005). In the tropics Vose et al do not make explicit calculations but scrutiny of their global map (their Figure 4) shows no evidence of relative warming of Tmin relative to Tmax in the tropics or extratropics separately since 1979.

The trend for HadCRUT3 global annual anomalies from 1979-2004 was 1.80 degrees/century. Halving the trend from Eurasia >45N in October-March reduces the global annual trend from 1979-2004 to 1.76 degrees/century. Removing the trend entirely from Eurasia >45N in October-March reduces the global annual trend from 1979-2004 to 1.72 degrees/century. The reason for this result is that warming over the period 1979-2004 is almost ubiquitous globally with the exception of most of Antarctica and a little of the Southern Ocean adjacent to it.”

This summary conflicts with the following text, which is based on peer reviewed papers also,

“Most of the recent warming has been in winter over the high mid-latitudes of the Northern Hemisphere continents, between 40 and 70° N (Nicholls et al., 1996). There has also been a general trend toward reduced diurnal temperature range, mostly because nights have warmed more than days. Since 1950, minimum temperatures on land have increased about twice as fast as maximum temperatures (Easterling et al., 1997). This may be attributable in part to increasing cloudiness, which reduces daytime warming by reflection of sunlight and retards the nighttime loss of heat (Karl et al., 1997)…….â€?

Part of the disagreement is possibly due to the different time periods selected. It is someone misleading in any case for the response to be in units of degrees per century, when the values thay quote should be, for example for the global average, 0.45 degrees per 25 years. Such a value is well within the range of amplified minimum temperature increases that we show to be realistic in the Pielke and Matsui GRL paper. We are also currently exploring a similar issue with respect to maximum temperatures and will report on this study when complete. Our research does support an increase of minumum temperature with time, but indicates that since the measurements are obtained near the surface, that the increase is overstated.

2. “The heights of the surface temperature observations are largely fixed, so an observed warming trend is not invalidated by any variation of trend with height.”

Where is their documentation that these heights are fixed? Studies are being performed because the heights of the temperature observations have been changed, and are funded by NOAA! See, for example,

Griffith, Brian D., and Thomas B. McKee, 2000:. Rooftop and Ground Standard Temperatures: A Comparison of Physical Differences. Climatology Report 00-2, Atmos. Sci. Paper 694, Dept. of Atmos. Sci., CSU, Fort Collins, CO, July, 49 pp.

3. “The cited paper by Pielke and Matsui appears to be an idealized calculation for some unspecified extreme nocturnal condition e.g. that might occur over the Prairies or Siberia.”

The model we used was based on obervations, as summarized in the classic textbook Stull, 1988: An Introduction to Boundary Layer Meteorology, Kluwer Academic Publishers. It accurately represents how the nightime boundary layer responds to a reduction in boundary layer cooling for any reason (i.e. with the result that there is an amplified increase of near surface air temperatures; thus sampling of temperatures near the surface results in a warm bias in terms of boundary layer averaged temperature trends). It is not an “extreme” case, but is true for any night which does not have significant horizontal temperature advection.

4. “Any attempt to quantify this effect globally or over the tropics requires a full assessment of the real mix of weather events that have occurred. This can only be approximately achieved by very carefully running a full climate model with a high-resolution boundary layer. ”

The use of a model to evaluate a hypothesis is not appropriate. Models have serious deficiences in their representation of the nighttime boundary layer (see; also there will be a weblog on this issue as soon as the issue on the GABL study appears in Boundary Layer Meterology). Real observational data representing real weather needs to be used to examine the magnitude of the warm bias. This should have been a recommendation of the CCSP Report (it was but it was deleted with the replacement Chapter 6).

5. “Furthermore, Pielke and Matsui do not take account of the fact that the radiative imbalance driving global warming is fundamentally at the tropopause rather than at the surface. The long-term average radiative imbalance at the land surface is very small when greenhouse gases are increasing, because increasing downward longwave radiation from the warming atmosphere balances increased upward longwave radiation from the warming surface.”

As we have shown in

Eastman, J.L., M.B. Coughenour, and R.A. Pielke, 2001: The effects of CO2 and landscape change using a coupled plant and meteorological model. Global Change Biology, 7, 797-815.

there is a significant reduction of cooling at night (which elevated the minimum temperatures; see Figure 8 in that paper), due to an increase of carbon dioxide. A reduction of cooling by 1 watt per meter squared is a realistic value.

6. “So Pielke and Matsui’s paper may have limited application”

The casual dismissal of the science issue that we raised in Pielke and Matsui exists throughout the CCSP Report whenever a diverse view is presented that does not conform to the views of the Committee Chair and the majority of the other members of the Committee.

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