NATURE OLOGY | ADVANCE ONLINE PUBLICATION | www.nature.com/natureology 1 T he recent recognition that humans are shaping climate change is a contemporary addition to a very long, historical recog- nition of how climate has shaped humans — especially the evolving patterns of social systems 1 . Indeed, it is plausible that key transitions in human evolutionary history have been driven in large part by climate change 2,3 . Changes in climate will doubtless be a key force in the future evolution of social systems, including all aspects of social, economic and political life, while impinging on the health and well-being of the individuals who populate them 4 . Considerable progress has been made in developing a better understanding of how human actions lead to environmental change and in particular on what is most oten called the anthropogenic drivers of climate change. By anthropogenic drivers we simply mean the range of human actions that cause climate change and the fac- tors that shape those actions. here are two major streams of research on anthropogenic driv- ers of climate change. One highly developed stream has focused primarily on land-use change and its impact on ecosystems. It is motivated not only by a concern with changes in albedo, but also with changes in the supply of ecosystem services, including carbon sequestration, and the emission of greenhouse gases from agricul- ture. his research stream is prominent in anthropology, geography and sociology, and most study designs focus on the household or local to regional landscape as the unit of analysis. As there have been several excellent recent reviews of this literature 5–7 , we will not repeat their indings in detail in the discussion that follows. Examination of the drivers of greenhouse-gas emissions, the sec- ond research stream, has been conducted by scholars mostly from economics, political science and sociology. Many studies examine diferences across nation states or other geopolitical units, such as cities, as it is typically at that level that institutions, policies and technological portfolios are organized. Furthermore, it is these units that deine the boundaries of governance and collect the types of data needed for analyses. A growing number of studies are also looking at the household level, where the challenge is to ind ade- quate data on energy consumption — the major source of emissions from households 8 . As greenhouse-gas emissions are the dominant driver of climate change and as studies of emissions at the national level have been less systematically reviewed than studies focused on land use, they are our focus here. Human drivers of national greenhouse-gas emissions Eugene A. Rosa 1,2 * and Thomas Dietz 3 Centuries of speculation about the causes of human stress on the environment is now being disciplined with empirical evidence, including analyses of diferences in greenhouse-gas emissions across contemporary nation states. The cumulative results can provide useful guidance for both climate projections and for policy design. Growing human population and aluence clearly contribute to enhanced environmental stress. Evidence does not support the argument for amelioration of greenhouse-gas emissions at the highest levels of aluence. However, the role of other factors, such as urbanization, trade, culture and institu- tions remains ambiguous. Consumption and population Candidate drivers have been discussed for decades, even centuries: population, aluence and consumption, choice of technolo- gies, institutional arrangements and culture. he general argu- ments stretch back at least to the writings of homas Malthus in the eighteenth and nineteenth centuries, and can be sketched quickly. Growing human population puts stress on the environ- ment. hat stress is conditioned not only by population size and rate of increase, but also on the patterns of consumption of the population. And consumption, in turn, is primarily a function of aluence. Culture may have some mitigating impact through the composition of consumption, but over the course of the past several decades, many forms of consumption seem to converge upwards to a Western pattern as aluence increases 9–11 . hus there are concerns with increases in consumption as average aluence increases in many nations, oten accompanied by the emergence of an aluent middle class. However, the stress on the environment produced by a popula- tion and its consumption also depends on the technology used to produce what is consumed. he critical point — elucidated nearly four decades ago in a debate between Barry Commoner, on one side, and Paul Ehrlich and John Holdren, on the other — is that population, aluence, technology and all other drivers act not alone or additively but in a multiplicative fashion 12–14 (Box 1). he projected increase in the human population to ten billion or more by the century’s end unquestionably threatens the carrying capac- ity of the planet 15 . he size of the impact that will occur depends on both patterns of consumption and the technology used to sup- ply it. It makes little sense to speak of the efects of population without simultaneously taking account of the efects of consump- tion and technology. Recent discussions have added nuances to arguments about population — the number of households may matter more than the number of people, shits in age structure may change consumption patterns, urbanization may have either deleterious or beneicial efects on the environment. To either understand the historical pattern of climate forcing, which can largely be attributed to the aluent nations, or to pro- ject future emissions, where nations rapidly increasing in aluence will probably be major contributors, we must test these conceptual arguments against empirical evidence. However, it is only in the 1 Department of Sociology, Washington State University, Pullman, Washington 99164, USA, 2 Woods Institute for the Environment, Stanford University, Stanford, California 94305, USA, 3 Department of Sociology, Environmental Science and Policy Program, Animal Studies, Michigan State University, East Lansing, Michigan 48824, USA. *e-mail: rosa@wsu.edu REVIEW ARTICLE PUBLISHED ONLINE: 10 JUNE 2012 | DOI: 10.1038/NCLIMATE1506 © 2012 Macmillan Publishers Limited. All rights reserved