March 17, 2004

For Land’s Sake

Filed under: Climate History

Industrialization and other changes in land use account for much of the 20th century’s surface temperature increase.

In recent months, we’ve reported on a number of studies that have appeared indicating land use change may well be a dominant component of the overall surface warming trend. These are acts that might, at first, seem climatically innocuous: For example, turning prairies into farms, or farms into cities. There have been some important recent findings:

* Land-use change and urbanization accounts for a significant portion of the surface temperature increase of the last century, an effect that is at least twice as great as has been previously estimated for the United States, according to Eugenia Kalnay and Ming Cai of University of Maryland. (Kalnay and Cai, 2003; see World Climate Alert, http://www.greeningearthsociety.org/wca/2003/wca_1b.html).

* A group of researchers from the Netherlands (Brandsma et al., 2003) demonstrated that urban heat island biases in surface temperature data are not confined to cities, but may spread to surrounding rural locations and causing urban heat island effects to be much larger in magnitude than previously thought (See World Climate Alert, http://www.greeningearthsociety.org/wca/2003/wca_3b.html).

In January, a paper given very prominent billing by the American Meteorological Society at its annual meeting demonstrated that there is a pervasive “economic” signal lurking in many global records heretofore thought to be bias-free. The work, by WCA’s own Pat Michaels and Canadian researcher Ross McKitrick, showed that, while “greenhouse” warming is dominant in cold areas of the Northern Hemisphere in the winter, the “economic” signal dominated elsewhere, especially in the summer.

Most recently, another Dutch research team determined that local surface changes caused by industrialization account for a significant portion of global temperature increases in recent decades. Jos de Laat and Ahilleas Maurellis, both at the Earth Oriented Science Division of the National Institute for Space Research in the Netherlands, published their findings in Geophysical Research Letters (de Laat and Maurellis, 2004).

Jos de Laat and Ahilleas Maurellis used an idea that Michaels and McKitrick employed, in which they defined local CO2 emissions as a proxy for the amount of local industrialization. They then divided the world up into “industrialized” and “non-industrialized” regions and calculated the temperature trends within each region. De Laat and Maurellis then repeated their analysis using a different cut-off value for what level of CO2 emissions defined industrial and non-industrial.

Using CO2 emissions as a proxy for industrialization has the added benefit that greenhouse gas emissions do not contain any long-term decadal trends or other biases related to natural temperature changes due to volcanoes or El Niño, and therefore provide an optimal representation of exactly those regions responsible for anthropogenic emissions.

The results of their analysis are presented in Figure 1. What they find is not surprising: Industrial regions with high CO2 emissions have significantly larger warming trends than non-industrialized regions, and larger trends than the globe as a whole. Similarly, as industrialization (as represented by CO2 emissions) increases, so does the temperature trend. That is true for both the surface and the balance of the lower atmosphere, or troposphere.

Comparing the trends among surface, lower-troposphere, and mid-troposphere, however, confirms the hypothesis that surface trends are larger than those in the free atmosphere. In fact, the trends in the lower troposphere are also lower than those in the middle troposphere. Given that non-industrialized regions show significantly smaller or even negligible temperature trends, the authors infer that a significant portion of the global warming temperature signal is localized—that is, confined to industrialized regions—and furthermore that the warming is indeed confined to the surface.

Temperature Trends

Figure 1. Mean temperature trends (ºC/decade) for 1979–2001 for industrialized regions (red) and non-industrialized regions (blue) for different CO2 emissions. The shaded regions indicate the uncertainties of the trend estimates. The thick solid bar inside the x-axis in each panel represents the global mean trend in each data set. (Adapted from de Laat and Maurellis (2004))

How does GCM output stack up in this simple industrialized vs. non-industrialized comparison? De Laat and Maurellis apply two of the climate models used in the Third Assessment Report of the United Nations Intergovernmental Panel on Climate Change (IPCC, 2001). No news there for readers of these pages: Those models completely miss reality. Instead of increasing temperature trends with increasing CO2 emissions, as demonstrated with the observational data, the models produce constant or even diminishing temperature trends for industrialized regions.

While they’re at it, the authors point out a serious flaw in the IPCC’s surface temperature record. According to the paper the “global” warming trend is about 0.2ºC per decade (it’s actually 0.17°/decade for the last quarter-century) but the data do not actually have global coverage. For instance, there’s virtually no information from Antarctica, which is known to have cooled slightly in recent decades. When the authors calculate the satellite-based temperature trend for the same regions actually covered by the IPCC, they find that the IPCC’s geographic selection results in an overestimation of warming by 33%. Applying this finding to the surface temperature data will reduce the “real” warming to something much smaller than 0.2ºC per decade commonly claimed

Once again, global warming theory and GCMs are found to be fundamentally flawed. A significant, if not dominant portion of temperature increases in recent decades has resulted from local surface heating processes due to land use change, urbanization, and even anthropogenic greenhouse gases.

References:

Brandsma, T., G. P. Konnen, and H. R. A. Wessels, 2003. Empirical estimation of the effect of urban heat advection on the temperature series of De Bilt (The Netherlands). International Journal of Climatology, 23, 829–845.

de Laat, A. T. J., and A. N. Maurellis, 2004. Industrial CO2 emissions as a proxy for anthropogenic influence on lower tropospheric temperature trends. Geophysical Research Letters, 31, L05204, doi:10.1029/2003GL019024.

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

Michaels, P.J., McKitrick, R., and P.C. Knappenberger, 2004. Economic signals in global temperature histories. Presented at the American Meteorological Society annual meeting, January.

Intergovernmental Panel for Climate Change (IPCC), 2001. Climate Change 2001: The Scientific Basis, Cambridge Univ. Press, New York.




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