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Non-CO2-Induced Anthropogenic Warming
De Laat, A.T.J. and Maurellis, A.N. 2006. Evidence for influence of anthropogenic surface processes on lower tropospheric and surface temperature trends. International Journal of Climatology 26: 897-913.

For the period 1979-2001, de Laat and Maurellis (2004) found that "measurements of surface and lower tropospheric temperature change give a very different picture from climate model predictions and show strong observational evidence that the degree of industrialization is correlated with surface temperature increases as well as lower tropospheric temperature changes." Specifically, they found that the surface and lower tropospheric warming trends of all industrial regions were greater than the warming trends of earth's non-industrial regions, and that the difference in warming rate between the two types of land-use grows ever larger as the degree of industrialization increases. These findings, in their words, "lend strong support to other indications that surface processes (possibly changes in land-use or the urban heat effect) are crucial players in observed surface temperature changes (Kalnay and Cai, 2003; Gallo et al., 1996, 1999)." Hence, they concluded that "the observed surface temperature changes might be a result of local surface heating processes and not related to radiative greenhouse gas forcing."

What was done
In their new paper, the two researchers sought to strengthen their earlier conclusions by employing two additional data sets and by analyzing the data with an additional statistical method. They also looked more closely for evidence of the industrialization-warming correlation in climate model simulations of enhanced greenhouse gas-induced warming.

What was learned
Quoting de Laat and Maurellis, "we have established that the correlation between observed near-surface temperature trends and CO2 emissions presented in de Laat and Maurellis (2004) occurs in a variety of data sets in a completely consistent way." They also confirmed that surface and satellite temperature measurements "display the same kind of temperature trend enhancements" and that they "are quite large and cover a sizable fraction of the globe (~10%)." In addition, the Dutch scientists "confirm[ed] the absence of the above correlation in climate model simulations of enhanced greenhouse gas warming."

What it means
De Laat and Maurellis say their findings suggest that over the last two decades non-greenhouse gas anthropogenic processes "have contributed significantly to surface temperature changes," which strengthens their earlier conclusion that "observed surface temperature changes might be a result of local surface heating processes and not related to radiative greenhouse gas forcing."

De Laat, A.T.J. and Maurellis, A.N. 2004. Industrial CO2 emissions as a proxy for anthropogenic influence on lower tropospheric temperature trends. Geophysical Research Letters 31: 10.1029/2003GL019024.

Gallo, K.P., Easterling, D.R. and Peterson, T.C. 1996. The influence of land use/land cover on climatological values of the diurnal temperature range. Journal of Climate 9: 2941-2944.

Gallo, K.P., Owen, T.W., Easterling, D.R. and Jameson, P.F. 1999. Temperature trends of the historical climatology network based on satellite-designated land use/land cover. Journal of Climate 12: 1344-1348.

Kalnay, E. and Cai, M. 2003. Impact of urbanization and land use change on climate. Nature 423: 528-531.

Reviewed 1 November 2006