Population growth and projection of future U.S. greenhouse gas outputs

Background/Question/Methods

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Almost all discussions of current and future anthropogenic greenhouse gas emissions focus on per-capita contributions.   Because total emissions are the product of number of people times an (average) per capita contribution it is essential that population estimates be included in projections of future emissions.   We utilize both our own and U.S. Census Bureau population projections to produce a matrix of plausible U.S. greenhouse gas futures during the 21^st century.   Population variables include fertility and immigration levels (both as functions of ethnic group), while per-capita variables include resource availability and economics, given the likelihood of dramatic changes in world markets and energy technologies.  Relationships among fertility, family planning, costs of reducing carbon emissions, and total greenhouse gas outputs are considered in 2009 studies from Oregon State University (P. Murtaugh and M. Schlax: “Reproduction and the carbon legacies of individuals”, Global Environmental Change 19, pp. 14-20) and the London School of Economics.

            A baseline projection of U.S. greenhouse gas emissions during the 21^st century can be grounded in measured emissions and population during the past 20 years as reported by the EPA and the U.S. Census Bureau.  Plausible variations from these baselines then give a range of projected future emissions.  The substantial sensitivity of emissions to unpredictable “glitches” in a business-as-usual scenario is well illustrated by the drop in greenhouse gas emissions arising from the deep economic recession that began in 2008.   The state of California is often in the vanguard of U.S. environmental legislation; future U.S. emissions, based on assumed (optimistic) U.S. adaptation of an “enlightened” California-like consumption model, will be estimated. 

Results/Conclusions

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Overall, given the deep divide between what many/most climate scientists (specifically those of The Intergovernmental Panel on Climate Change), regard as essential greenhouse gas emission reductions to avoid environmental catastrophes, and the history of U.S. per capita consumption and endless population growth, there is no reason for optimism.  The U.S. has never had a long-range population policy, the dominant military-industrial complex is slow to adjust to essential new realities, and the U.S. consumer has become conditioned to some of the highest per capita resource use on the planet.