(Statistics, Politics, and Policy, Volume 1, Issue 1, July 2010)
Gridded land surface temperature data products are used in climatology on the assumption that contaminating effects from urbanization, land-use change and related socioeconomic processes have been identified and filtered out, leaving behind a “pure” record of climatic change.
But several studies have shown a correlation between the spatial pattern of warming trends in climatic data products and the spatial pattern of industrialization, indicating that local non-climatic effects may still be present.
This, in turn, could bias measurements of the amount of global warming and its attribution to greenhouse gases. The 2007 report of the Intergovernmental Panel on Climate Change (IPCC) set aside those concerns with the claim that the temperature-industrialization correlation becomes statistically insignificant if certain atmospheric circulation patterns, also called oscillations, are taken into account. But this claim has never been tested and the IPCC provided no evidence for its assertion. I estimate two spatial models that simultaneously control for the major atmospheric oscillations and the distribution of socioeconomic activity. The correlations between warming patterns and patterns of socioeconomic development remain large and significant in the presence of controls for atmospheric oscillations, contradicting the IPCC claim. Tests for outlier influence, spatial autocorrelation, endogeneity bias, residual nonlinearity and other problems are discussed.
Direct testing refutes the IPCC’s assertion that “the correlation of warming with industrial and socioeconomic development ceases to be statistically significant” upon controlling for atmospheric circulation patterns.
The correlations are quite robust to the inclusion of atmospheric circulation indicators, confirming the presence of significant extraneous signals in surface climate data on a scale sufficient to account for about half the observed upward trend over land since 1980.
As discussed in the underlying papers by deLaat and Maurellis and McKitrick and Michaels, socioeconomic activity can lead to purely local atmospheric modifications (such as temporary increases in local particulates and aerosols) as well as land-surface modifications and data inhomogeneities, and these can cause apparent trends in temperature data that should not be interpreted as general climatic changes. As was noted half a century ago by J. Murray Mitchell Jr., “The problem remains one of determining what part of a given temperature trend is climatically real and what part the result of observational difficulties and of artificial modification of the local environment.” (Mitchell Jr., 1953).
The results herein show that this longstanding concern is likely still relevant, and the hypothesis used by the IPCC to dismiss it cannot be supported by the data. A substantial fraction of the post-1980 trends in gridded climate data over land are likely not “climatically real” but result from data quality problems and local environmental modifications.
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h/t to populartechnology.net