Infrastructure protectionCO2 emissions as a result of economic growth, decline not symmetrical

Richard York, a researcher with the Department of Sociology and Environmental Studies Program at the University of Oregon, has just published an article in Nature Climate Change in which he says that estimating the trajectory of CO2 emissions, an important part of planning for climate change mitigation and adaptation, depends in part on understanding how these emissions are influenced by the economy.

Researchers have developed sophisticated models of the connections between the economy and CO2 emissions, but prominently used modeling approaches implicitly assume that the effect on emissions of declining GDP per capita is symmetrical with the effect of growth in GDP per capita.

Analyzing available data from 1960 to 2008, York finds, however, that in years when GDP per capita shrinks, CO2 emissions per capita do not decline in equal proportion to the amount by which they increase with economic growth. One important implication of this finding is that CO2 emissions depend not only on the size of the economy, but also on the pattern of growth and decline that led to that size.

York estimated two separate models of CO2 emissions (from fossil-fuel combustion and cement manufacturing) per capita using first-differenced (that is, change from year to year) variables. He estimated different slopes for when the change in GDP per capita was positive (economic growth) and when it was negative (economic decline). All variables were converted to natural logarithmic form before first-differencing, making these elasticity models. York notes that the use of first-differenced data controls for factors that vary across nations but do not change over the period of observation, such as many aspects of physical geography.

— Read more in Richard York, “Asymmetric effects of economic growth and decline on CO2 emissions,” Nature Climate Change (7 october 2012) (doi:10.1038/nclimate1699)