For decades economists have tried to link energy use and GDP. However, this has grown more tortured over time, as GDP gets increasingly divorced from the material inputs that consume large quantities of energy. As developed countries shift more of their efforts into services and out of industrial production, our GDP grows quickly, as services ultimately give more bang for the buck, and this flatters our figures regarding energy intensity.

This leads to tortured projections that are increasingly less useful.

Other analysis focuses on supply constraints and costs. The Department of Energy’s Energy Information Administration is really keen on showing how much fossil fuels are going to cost and make that a key part of their models of future consumption. But in country after country we see that, once a certain level of per capita income (and not GDP) is reached, energy is not truly constrained by supply–people will pay whatever it costs. Modelling costs and availability is really a good idea for countries like India. It’s not nearly as useful for countries like the U.S. This is one of the reasons why the DOE’s EIA has to keep adjusting figures.

However, energy consumption is far more tightly linked to population. And every analysis pays lip service to that fact. The EIA Annual Energy Outlook 2012 says, “Population is a key determinant of energy consumption through its influence on demand for travel, housing, consumer goods and services.” And then they promptly move on to other topics.

The fact is that we consume one quad of energy for every 3 million inhabitants in this country. If we get 3 million more immigrants or children born tomorrow, we will consume one more quad than we otherwise would have.

Population is the principal component of energy consumption.

Our population is growing.

You will have to make a very good case to convince me that the easiest way to estimate future energy consumption in America is anything other than to add one quad to our total for every cohort of 3 million new humans in the U.S. of A. By way of checking, our energy consumption was more than 1 quad per 3 million people in 1990, and also in 1980–so I don’t think I’m exaggerating for effect here.

The U.S. Census Bureau has published estimated populations through 2100. They took four guesses–the series was published in 2000 and their highest growth series is bang on accurate. Most estimates use what they called their Middle Series, but their Middle Series predicted a 2010 population of less than 300 million. If it’s that far out after just a decade, I don’t really want to use it for a century. What they called their High Series was much better, so I’m going with it. (But I’ll show a couple of figures later with the Middle Series.)

Our current population is 311 million. We consumed 98 quads in 2010. So here are the Census Bureau’s High Series projections at 10 year intervals, with my highly sophisticated algorhythm for calculating additional energy consumption (add 1 quad for every 3 million people):

2020 354,642,000 people 113 quads

2030 409,604,000 people 130 quads

2035 441,648,000 141 quads

2040 475,949,000 people 153 quads

2050 552,757,000 people 179 quads

2060 642,752,000 people 209 quads

2070 749,257,000 people 244 quads

2075 809,243,000 people 264 quads

2080 873,794,000 people 286 quads

2090 1,017,344,000 people 333 quads

2100 1,182,390,000 people 388 quads

Sobering totals. Obviously, the DOE used the Census Bureau’s Middle Series for their projections, so let’s show a couple of years using that list. But for the moment, let’s hang on to my little conceit that calculating future energy consumption can be simple arithmetic, rather than convoluted conjecturing.

2035 353,749,000 people 112 quads

2050 403,687,000 people 129 quads

2075 480,504,000 people 155 quads

2100 570,904,000 people 185 quads

Now remember that the EIA only projects energy consumption through 2035. Their projection for that year was 108 quads, revised down from 114 quads because they felt that energy efficiency and (???) an improving economy (???) would lower energy consumption. My back of the envelope calculations show 112 quads for 2035 using their choice of the population estimates, and 141 quads if the High Series continues to be more accurate.

My totals amount to 0.61% CAGR using the Middle Series and 1.47% using the High Series. Remember also that last year’s growth in energy consumption was 3.9%.

Population growth using the High Series from the Census Bureau is 1.49% CAGR. Using the Middle Series shows population growth at 0.68%.

So I would say we have a range of possible energy consumption figures that vary between 112 and 141 quads at 2035, between 129 and 179 quads at 2050 and between 185 and 388 quads at 2100.

This would seem to put into question the EIA’s projections of future energy consumption for the U.S. If the High Series is accurate, and if my crude metric is closer to reality than the EIA’s supply-dominated but sophisticated model, energy growth in the U.S. will be 1.54% per year, rather than the 0.39% the EIA forecasts.

Sadly, given what we have seen regarding Mexico and Turkey, this would almost force us to conclude that the EIA was as overly optimistic about energy consumption in the OECD as it was for developing countries.

Now, honestly, it is my hope that the light-hearted tone of this post is enough to convince readers that I don’t really intend to suggest that a mere calculation of population growth is an adequate substitution for serious thought about energy consumption. There is more to it than just simple arithmetic. But serious thinking is more than just additional calculations.

Population growth generates momentum towards a certain level of energy consumption. Efforts to lower than consumption through energy efficiency and innovation will fight strong headwinds created by this population growth. But just as my argument is not totally serious, neither are arguments that energy efficiency alone will dramatically lower consumption. The difference is that I acknowledge the incompleteness of my arguments…