Skip to main content

Energy related world CO2 emissions reached a threateningly high historical maximum of 30,600 millions of tonnes in 2010, according to the International Energy Agency (IEA). Just consider that in order to limit global temperature increase to 2 ºC global energy-related emissions must not exceed 32,000 millions of tonnes in 2020. In consequence, in the next ten years emissions must increase at a five times lower rate than in the last ten years, which demands radical measures at all levels, from citizenship to governments and international organizations.

Such energy policies are centred in increasing efficiency and in the development/use of green energy. Some of the solutions proposed are using biofuels, solar energy, hydropower, etc. But there is a factor influencing emissions which is not usually presented to the public and has not received much attention by climate change researchers or in energy policies. It is the effect of an unstoppably growing population, all of its members consuming energy.

Figure 1: CO2 emissions and Population in the period 1971-2008. Source: IEA (2010)

To study the effect of population on CO2 emissions the IPAT equation has often been used. This equation summarizes the different factors affecting greenhouse gas emissions:


It means that environmental impact (I) depends on population size (P), affluence (A) measured as per-capita income, and technology (T) as environmental impact per unit of economic production. Modifications of this formula have also been used to analyse other demographic effects on CO2 emissions with eye-opening results. L. Jiang from the National Center for Atmospheric Research at Boulder (CO) and K. Hardee from Population Action International have recently reviewed these effects.

The fact that greenhouse gas emissions are parallel to population growth, increases in energy consumption and economic growth has been known for a while. Statistical analyses of historical data of different countries show that for each one per cent increase in population, CO2 emissions increase by approximately 1% (ranging between 0.98-1.43 per cent depending on the data set used). In fact, population size is the only demographic variable used by most of models used to assess climate change effects. However, demographic effects on greenhouse gas emissions have been mostly studied by demographers, sociologists, or ecologists, who use a different type of language and different models than climate change researchers. Were not for this lack of permeability between research fields, climate change researchers would have been able to include other demographic variables in their assessments. Statistical analyses have shown complex demographic effects due to different population groups (urban vs. rural communities, different age groups, households of different size) using energy in different ways and with varying intensity.

Household size effects on emissions depend on economies of scale effects and the fact that households are the unit of consumption in developed countries. In fact, in most industrialised countries, the number of households explains better the increase in emissions than population size: while population size explains 18% of the increase in emissions from 1970 to 1990, the number of households accounts for 42% of the increase. The reason is that the decrease in the average size of households has made the number of households increase much faster than population size. Also, small households consume energy less efficiently than larger households and the consumption per capita is higher, resulting in increased CO2 emissions even if population growth has slowed down. As an example, a single fridge can serve a four-member family. But you need four fridges for four one-person households. Now think about washing machines, dishwashers, cars…

The composition of the household is also important to explain CO2 emissions. Living with a retired householder tends to increase energy use at home and to reduce transportation energy use. According to the UN, the proportion of elderly (more than 60 years old) in the world population in 2050 will double, passing from one in ten people to somewhat more than two in ten people. In the US, the expected change in population distribution age during the next 40 years will contribute to the reduction of CO2 emissions according to a study by E. Zagheni from the University of California, Berkeley. However, these results are uncertain since we cannot know how consumption patterns will evolve in the future. For example, medical science advances may help younger generations attain retirement age in better health conditions, allowing them to carry a more active life for longer -and use more transportation and work-related energy. The study does not take into account either increases in retirement age, which many developed countries have already approved or are pondering. Or, living longer, the proportion of disabled and physically or mentally impaired people might increase and more home aid and technical disability adaptations might be necessary, conducing to an increase in residential energy.



  • IEA (2010) CO2 emissions from fuel combustion. Highlights. Available at
  • Jiang, L., Hardee, K. (2011) How do Recent Population Trends Matter to Climate Change? Population Research and Policy Review 30, 287-312. doi: 10.1007/s11113-010-9189-7
  • Zagheni, E. (2011) The Leverage of Demographic Dynamics on Carbon Dioxide emissions: Does Age Structure Matter? Demography 48, 371-399. doi:10.1007/s13524-010-0004-1

Leave a Reply

Significance Magazine