|Fig. 1: Images of minimum sea ice concentration for 1979 (left) and 2003 (right). (Courtesy of NASA. )|
This report examines the Earth's ability to support the current human population. Specifically, can the Earth sustain human life if everyone in the world consumed enough energy to make themselves happy? I use a recent academic survey to classify individual happiness, utilize this measure to assess the current status of the United States population, and subsequently extrapolate these numbers to identify the potential consumption of the entire world.
There is clearly a lot of literature surrounding the issue of US vs. global consumption; popular websites will even calculate your total global footprint, but I am interested in sufficiency.  If it was globally distributed, do we currently generate enough energy to satisfy the world's demand? How much do we actually need to generate to live satisfying lives?
Kahneman and Deaton have recently proposed that happiness - one's everyday satisfaction with life - saturates at an income level of $75,000 ($US).  They used several quantitative measures to show that, while Americans will rate their overall satisfaction with life continuously higher depending on their income level, their actual day-to-day happiness stops increasing after $75k. This level of income is thus a present-day metric of how much a household must consume to be happy in the US.
Let us now make the simple assumption that income is proportional to energy consumption and ask how much energy the US would have to consume to make all Americans happy. The present mean household income in the US is $67.8 k.  It would thus have to increase by the factor
to satisfy the Kahneman-Deaton criterion. According to the CIA World Factbook, the US consumed 1.17 × 1020 joules in 2007.  The energy required to make all Americans happy in 2007 would have been
or just 11% more than the U.S. actually consumed.
Using the same reasoning, we may now calculate how much energy would be required to make everyone in the world happy. According to the CIA World Factbook the U.S. and world populations were 3.07 × 108 and 6.78 × 109, respectively.  The amount of energy required to make all 6.8 billion people happy would then be
|6.78 × 109
3.07 × 108
|× 1.29 × 1020 joules/year||=||2.85 × 1021 joules/year|
or 5.7 times the actual world energy consumption in 2007 ($5.0 × 1020 joules). [4,5] A 6-fold increase in energy consumption would, of course, mean a 6-fold increase the annual CO2 emissions for the world coming at a time when the safe global concentration for CO2 in the atmosphere (350 ppm) had already been exceeded. [6-10] According to The Worldwatch Institute, the consequences are potentially dire:
"Even if emissions slow, their tendency to raise temperatures lasts long into the future. CO2 concentrations are expected to rise for decades after emissions peak, and temperatures could continue going up for centuries, depending on when emissions stabilize. A 2008 study calculated that even if greenhouse gas concentrations in the atmosphere stabilize at 2005 levels, it would be impossible to avoid a total warming of 1.4 - 4.3 degrees Celsius above preindustrial levels by the end of this century." 
One could use the US calculations to contend that moderate consumption brings happiness and that the US has done well to enable its inhabitants to reach this level. The report numbers used are averaged and hide an interesting detail. The 2009 median household income was only $50, 007.  Half of the households in the US make roughly $25,000 less or 2/3 the needed income to be happy.
In any event, the Earth cannot support everyone consuming at the $75,000 level. People of other cultures, with their unique norms and memes, may not need to consume at this level to be happy. This might be a trait specific to the US. Perhaps other nations can find happiness in culturally specific manners without having to develop to the US level. What are we working for, if it is not happiness?
© Paul A. Cook. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Carbon Footprint Calendar," The Nature Conservancy.
 D. Kaneman and A. Deaton, "High Income Improves Evaluation of Life But Not Emotional Well-Being," Proc. Natl. Acad. Aci. 107, 16489 (2010).
 "The 2010 Statistical Abstract," U.S. Census Bureau.
 "The World Fact Book," United States Central Intelligence Agency.
 "2009 Annual Energy Review (AER)," US Energy Information Administration.
 L. Starke, ed., "Vital Signs 2010," Worldwatch Institute, p. 46.
 "Millennium Development Goals Indicators," United Nations Statistics Division.
 "Recent Mauna Loa CO2," U.S. Department of Commerce, National Oceanic and Atmospheric Administration.
 J. Hansen et al., "Target Atmospheric CO2: Where Should Humanity Aim?" Open Atmosph. Sci. J. 2, 217 (2008).
 E. H. Thompson and K. Ramanujan, "Recent Warming of Arctic May Affect Worldwide Climate," 23 Oct 03.