Trends in urban CO2 emissions and their relationship with development
The world's cities are already responsible for the majority of energy consumption and rapid urbanisation is increasing their dominance. Inconsistent definition and limited data has made it difficult to compare emissions trends among the world's big cities. Here we use a series of remotely sensed proxies to estimate both the size of cities each year and their emissions. We decompose the emissions trends into changes in area, population density and per capita emissions. We see three dominant clusters. Most developed countries show significant growth in urban area counterbalanced by decreasing per capita emissions. Developing countries show increases in both these terms with per capita emissions rising faster in cities than in the country as a whole.
Almost alone among developing countries, China shows a "developed" pattern with rapid increases in area but reductions in per capita emissions; most likely a result of explicit policies around urban air quality. We also see a negative correlation between population density and per capita emissions, supporting the role of densification in emissions reduction. The results suggest that urbanisation is likely to remain a driver of accelerating emissions for some time but that this may reverse with continued economic development.
Prof Rayner is Acting Director of the College. His main research activities focus on the estimation of surface sources and sinks of CO2. He uses satellite and in-situ measurements with models to quantify and understand the patterns and mechanisms of CO2 release and uptake with a focus on the tropics and Southern Hemisphere. In 2002, Prof Rayner was awarded the Priestley Medal of the Australian Meteorological and Oceanographic Society, the major research award in this field within Australia. Prof Rayner originally studied theoretical physics and mathematics at the University of Melbourne, Australia, where he completed a PhD in paleoclimate in 1991. After a brief foray into atmospheric dynamics he has spent the past two decades studying the carbon cycle at various scales and its interaction with the climate. He has concentrated on the application of statistical inference (going under various names such as inverse modeling or data assimilation) to problems in biogeochemistry. Prof Rayner has also worked at the National Center for Atmospheric Research and Princeton University in the US, CSIRO and Monash University in Australia and the Laboratory for the Science of Climate and the Environment in France. He currently holds an Australian Professorial Fellowship at the University of Melbourne.