Caldeira Lab

Attribution of Atmospheric CO2 and Temperature Increases To Regions: Importance of Preindustrial Land Use Change

Julia Pongratz & Ken Caldeira

When evaluating the historic contributions made by different countries to the greenhouse gasses found in Earth's atmosphere, calculations generally go back no further than the year 1840. In this study, we show that carbon dioxide contributions from the pre-industrial era as caused by clearing of natural vegetation for agricultural expansion still have an impact on our climate today.

Pongratz, J., and K. Caldeira, 2012: Attribution of atmospheric CO 2 and temperature increases to regions: importance of preindustrial land use change. Environmental Research Letters, 7, 034001, doi:10.1088/1748-9326/7/3/034001.




The historical contribution of each country to today’s observed atmospheric CO2 excess and higher temperatures has become a basis for discussions around burden-sharing of greenhouse gas reduction commitments in political negotiations. However, the accounting methods have considered greenhouse gas emissions only during the industrial era, neglecting the fact that land use changes (LUC) have caused emissions long before the Industrial Revolution. Here, we hypothesize that considering preindustrial LUC affects the attribution because the geographic pattern of preindustrial LUC emissions differs significantly from that of industrial-era emissions and because preindustrial emissions have legacy effects on today’s atmospheric CO2 concentrations and temperatures. We test this hypothesis by estimating CO2 and temperature increases based on carbon cycle simulations of the last millennium. We find that accounting for preindustrial LUC emissions results in a shift of attribution of global temperature increase from the industrialized countries to less industrialized countries, in particular South Asia and China, by up to 2-3%, a level that may be relevant for political discussions. While further studies are needed to span the range of plausible quantifications, our study demonstrates the importance of including preindustrial emissions for the most scientifically defensible attribution.


Figure: Contribution (in %) of world regions to atmospheric CO2 excess in years AD 1000-2006. The attribution of the CO2 excess for example in AD 1500 is a consequence of the emissions from AD 800 to 1500 in each region and global uptake of the ocean and the terrestrial vegetation. Before 1850, land use changes are driving the CO2 excess (bold colors), with largest contributions from China and South Asia (a region including India). After 1850, emissions from fossil-fuel burning become increasingly important (pale colors) and lead to the major part of today's CO2 excess being attributed to the industrialized regions. Considering the pre-industrial land use change emissions alters attribution of today's atmospheric CO2 excess and temperature increase to regions by 2-3%