The multi-decadal global surface temperature trend is used (inappropriately; e.g. see) as the primary metric to diagnose the magnitude of global warming and cooling. This post lists major unresolved issues with the use of this surface temperature trend metric, along with examples of recent papers and weblog posts that build on the set of problems identified in our paper
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.
Issues with the global average surface temperature trend assessment [the sections are from the Pielke et al 2007 paper]:
- The use of one average temperature trend, which neglects that long wave cooling is proportional to the 4th power of temperature. This is a warm bias if the predominance of temperature increases are at cold absolute temperatures and a cool bias if at warm absolute temperatures [Section 2].
- There is a warm (cool) bias when the temperature measurements are just at one level near the surface and an overlying stably stratified boundary layer warms (cools) [Section 3].
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.
Lin, X., R.A. Pielke Sr., K.G. Hubbard, K.C. Crawford, M. A. Shafer, and T. Matsui, 2007: An examination of 1997-2007 surface layer temperature trends at two heights in Oklahoma. Geophys. Res. Letts., 34, L24705, doi:10.1029/2007GL031652.
Klotzbach, P.J., R.A. Pielke Sr., R.A. Pielke Jr., J.R. Christy, and R.T. McNider, 2009: An alternative explanation for differential temperature trends at the surface and in the lower troposphere. J. Geophys. Res., in press.
- The use of temperature data from poorly station sited locations introduces local non-spatially representative climate effects. This could be either a warming or cooling effect when the local environment of the siting changes over time [Section 4].
Brooks, Ashley Victoria. M.S., Purdue University, May, 2007. Assessment of the Spatiotemporal Impacts of Land Use Land Cover Change on the Historical Climate Network Temperature Trends in Indiana. Major Professors: Dev Niyogi and Michael Baldwin.
Jamiyansharav, K., D. Ojima, and R.A. Pielke Sr., 2006: Exposure characteristics of the Mongolian weather stations. Atmospheric Science Paper No. 779, Colorado State University, Fort Collins, CO 80523, 75 pp.
Watts, A. 2009: Is the U.S. Surface Temperature Record Reliable? 28 pages, March 2009 The Heartland Institute.
- The effect of concurrent multi-decadal near surface water vapor trends complicates the interpretation of long term temperature trends. If the location becomes drier (wetter) the actual heat in Joules of the surface air can decrease (increase) due just to this effect even if the long term surface temperature trend were zero [Section 5].
Davey, C.A., R.A. Pielke Sr., and K.P. Gallo, 2006: Differences between near-surface equivalent temperature and temperature trends for the eastern United States – Equivalent temperature as an alternative measure of heat content. Global and Planetary Change, 54, 19–32.
Fall, S., N. Diffenbaugh, D. Niyogi, R.A. Pielke Sr., and G. Rochon, 2009: Temperature and equivalent temperature over the United States (1979 – 2005). Int. J. Climatol., submitted.
- There remains an important statistical spread with the time of observation and instrument adjustments which necessarily introduces an uncertainty in the magnitude of the long term trends in surface air temperatures [Section 6] . There is also the dependence of nearby surface stations when the “homogenization” of the surface temperature trend data is applied in order to calculate a regional average [Section 7]. This later effect reduces the confidence in the magnitudes of the trends that are obtained since the stations are adjusted to some extent to conform to each other.
Pielke Sr., R.A. J. Nielsen-Gammon, C. Davey, J. Angel, O. Bliss, N. Doesken, M. Cai., S. Fall, D. Niyogi, K. Gallo, R. Hale, K.G. Hubbard, X. Lin, H. Li, and S. Raman, 2007: Documentation of uncertainties and biases associated with surface temperature measurement sites for climate change assessment. Bull. Amer. Meteor. Soc., 88:6, 913-928.
- The effect of land use/land cover change on the surface temperature trends [Section 9]. This effect seems to be mostly a warming effect, although situations such as conversion to irrigation would be cooling effect during the growing season.
Mahmood, R., R.A. Pielke Sr., K.G. Hubbard, D. “>Niyogi, G. Bonan, P. Lawrence, B. Baker, R. McNider, C. McAlpine, A. Etter, S. Gameda, B. Qian, A. Carleton, A. Beltran-Przekurat, T. Chase, A.I. Quintanar, J.O. Adegoke, S. Vezhapparambu, G. Conner, S. Asefi, E. Sertel, D.R. Legates, Y. Wu, R. Hale, O.W. Frauenfeld, A. Watts, M. Shepherd, C. Mitra, V.G. Anantharaj, S. Fall,R. Lund, A. Nordfelt, P. Blanken, J. Du, H.-I. Chang, R. Leeper, U.S. Nair, S. Dobler, R. Deo, and J. Syktus, 2009: Impacts of land use land cover change on climate and future research priorities. Bull. Amer. Meteor. Soc., Submitted.
Fall, S., D. Niyogi, A. Gluhovsky, R. A. Pielke Sr., E. Kalnay, and G. Rochon, 2009: Impacts of land use land cover on temperature trends over the continental United States: Assessment using the North American Regional Reanalysis. Int. J. Climatol., DOI: 10.1002/joc.1996.
We look forward to further papers on these uncertainties and biases in the use of the use of the surface air temperature to diagnose global climate heat changes. To avoid these problems with respect to their use to diagnose global warming and cooling, however, upper ocean heat content changes should be adopted as the primary approach, as recommended most recently in
Pielke Sr., R.A., 2008: A broader view of the role of humans in the climate system. Physics Today, 61, Vol. 11, 54-55
Douglass, D.H. and R. Knox, 2009: Ocean heat content and Earth’s radiation imbalance. Physics letters A.