Comments
Up to Half of Global Warming Since the 1980s is Due to Non-Climatic Processes
Ross McKitrick has had a paper accepted in a good journal which confirms his earlier work that up to half of the warming since 1980 is due to non-climatic processes such as urbanisation, land use change and socio-economic processes.
A pdf of the pre-print is available here.
Atmospheric Circulations do not Explain the Temperature-Industrialization Correlation*
Abstract:
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.
Key words: global warming, data quality, industrialization, spatial regression
Conclusions:
Regional patterns of industrialization, land-use change and variations in the quality of temperature monitoring have been shown by several groups of authors to leave significant imprints on climate data, adding up to a widespread net warming bias that may account for as much as half the post 1980 warming over land. The Fourth Assessment Report of the IPCC dismissed this evidence with the claim that “the correlation of warming with industrial and socioeconomic development ceases to be statistically significant” upon controlling for atmospheric circulation patterns. This claim was presented without any supporting statistical evidence. The models in this paper implement a reasonable way of augmenting the original regressions with the relevant oscillation data, and the results contradict the IPCC claim. The temperature-industrialization correlations in question are quite robust to the inclusion of standard measures of the effects of atmospheric circulation patterns on temperatures, confirming the presence of significant extraneous signals in surface climate data on a scale that may 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 changes in water vapour and fine particle levels), which, along with other land-surface modifications and data inhomogeneities, can cause apparent trends in temperature data that are not attributable to general climatic changes. As was noted half a century ago by J. Murray Mitchell Jr., referring to the use of temperature observations for measuring climatic trends, “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 concern is still valid, and the conjecture invoked by the IPCC to dismiss it is not supported by the data. A substantial fraction of the post-1980 trends in gridded climate data over land are likely not “climatically real” but arise from measurement quality problems and local environmental modifications.