There is a remarkable presentation of viewpoints on our Klotzbach et al (2009) paper by Michael Tobis (see) and James Annan (see). On Roger Pielke Jr.’s Blog, he has already posted effectively in response to Michael Tobis’s admission of his lack of expertise on the topic of our paper (see). From the comment below that James Annan made on his weblog, it is clear he does not understand boundary layer physics either. He wrote
“For the record, I agree that land use cover change may impact on the climate. But unless Roger Pielke can find some way of arguing that this has changed the net average surface flux by the order of 1Wm-2at night, his whole theory is still a bust. And even if he did, it would not rescue his erroneous claims that the trends in temperature due to GHG or the other most significant forcings induce a significant change in the lapse rate in the boundary layer.”
His challenge to document a change in the net surface flux by 1Wm-2 due to landscape change is a clear demonstration that he is poorly informed about boundary layer dynamics.
As one example of many, for urban areas relative to residential areas (which illustrate how the fluxes change as urbanization occurs), the paper
Soushi, K. and Y. Yamaguchi, 2007: Estimation of storage heat flux in an urban area using ASTER data. Remote sensing of environment ISSN 0034-4257
summarizes their study in the abstract
“The urban heat island phenomenon occurs as a result of the mixed effects of anthropogenic heat discharge, increased use of artificial impervious surface materials, and decreased vegetation cover. These factors modify the heat balance at the land surface and eventually raise the atmospheric temperature. It is important to quantify the surface heat balance in order to estimate the contributions of these factors. The present authors propose the use of storage heat flux to represent the heat flux between the land surface and the inside of the canopy for the heat balance analysis based on satellite remote sensing data. Surface heat fluxes were estimated around the city of Nagoya, Japan using Terra ASTER data and meteorological data. Seasonal and day-night differences in heat balance were compared using ASTER data acquired in the daytime on July 10, 2000, and January 2, 2004 and in the nighttime on September 26, 2003. In the central business and commercial districts, the storage heat flux was higher than those in the surrounding residential areas. In particular, in winter, the storage heat flux in the central urban area was 240 to 290 W m-2, which was much larger than the storage heat fluxes in residential areas, which ranged from 180 to 220 W m-2. Moreover, the negative storage heat flux in the central urban area was greater at night. This tendency implies that the urban surface stores heat during the daytime and discharges it at night. Extremely large negative storage heat flux occurred primarily in the industrial areas for both daytime and nighttime as a result of the enormous energy consumption by factories.”
These values are much larger than the 1Wm-2 threshold that James presented in his weblog.
On his statement rejecting “that the trends in temperature due to GHG or the other most significant forcings induce a significant change in the lapse rate in the boundary layer“, as just one example (and there are many), the paper
Sun, J-L et al, 2003: Heat balance in the nocturnal boundary layer during CASES-99 J. Appl. Meteorology. 42, 1649-1666
reported a “[A] radiative flux difference of more than 10 W m-2 over 46 m of height was observed under weak-wind and clear-sky conditions after hot days.”
The abstract reads
“A unique set of nocturnal longwave radiative and sensible heat flux divergences was obtained during the 1999 Cooperative Atmosphere-Surface Exchange Study (CASES-99). These divergences are based on upward and downward longwave radiation measurements at two levels and turbulent eddy correlation measurements at eight levels. In contrast to previous radiation divergence measurements obtained within 10 m above the ground, radiative flux divergence was measured within a deeper layer-between 2 and 48 m. Within the layer, the radiative flux divergence is, on average. comparable to or smaller than the sensible heat flux divergence. The horizontal and vertical temperature advection, derived as the residual in the heat balance using observed sensible heat and radiative fluxes, are found to be significant terms in the heat balance at night. The observations also indicate that the radiative flux divergence between 2 and 48 m was typically largest in the early evening. Its magnitude depends on how fast the ground cools and on how large the vertical temperature gradient is within the layer. A radiative flux difference of more than 10 W m-2 over 46 m of height was observed under weak-wind and clear-sky conditions after hot days. Wind speed variation can change not only the sensible heat transfer but also the surface longwave radiation because of variations of the area exposure of the warmer grass stems and soil surfaces versus the cooler grass blade tips. leading to fluctuations of the radiative flux divergence throughout the night.”
As the authors write “Its magnitude depends on how fast the ground cools and on how large the vertical temperature gradient is within the layer…..Wind speed variation can change not only the sensible heat transfer but also the surface longwave radiation because of variations of the area exposure of the warmer grass stems and soil surfaces versus the cooler grass blade tips. leading to fluctuations of the radiative flux divergence throughout the night.”
All of us should be disappointed that both James Annan and Michael Tobis have elected not to engage in a proper scientific discussion of our findings. We look for a dialog with colleagues who do undertand boundary layer dynamics.