In order to reduce the use of fossil fuels, we need to increase the use of renewable sources of energy. At least, so the theory goes. However, a new study published in Nature Climate Change challenges this assumption, demonstrating that, rather than displacing fossil fuels, alternative sources of energy barely outpaced increasing demand over the last 50 years.

The paper was written by Richard York, a professor at the University of Oregon. In it, he looks at past energy use and electricity generation from fossil fuels and alternative sources for about 130 countries. Here, “alternative sources” means nuclear, hydro, and non-hydro renewables like wind, solar, geothermal, tidal, biomass, and biofuels.

In the paper, York essentially tries to determine if the added energy/electricity production from these alternatives actually displaced fossil fuels, or if the increase in capacity just kept up with rising demand. To do this, he looked at historical data for energy use and electricity production, and created two models for electricity demand.

The first model controlled for demand just by using per-capita gross domestic product (GDP) over the past 50 years. This was justified because, in general, energy production has roughly paralleled increased economic activity for much of this period. A second model added additional variables to better account for changes in demand, like urbanization, manufacturing, and the ratio of the dependent population (under 16 and over 64) to non-dependents. Due to the need for more complex data, this model was limited to the past 30 years, but the results are similar to the first model.

Essentially, both models fit a curve to the data, where the independent variable was the production from alternative sources. The dependent variable was the total electricity/energy production multiplied by the proportion from fossil fuels, divided by the total population. There would then be a data point for each nation at each year for which data is available.

York found that each kilowatt-hour (kWh) of electricity generated from non-fossil-fuel sources displaced only 0.089 kWh of that from fossil fuels. To put this in perspective, displacing one kWh of fossil-fuel electricity would require over 11 kWh of electricity from alternative sources. The second, more complex model gave similar, but slightly worse, results.

Using the same models but looking at total energy use—for example, transportation in addition to electricity generation—the data looks a little better. He found that each unit of energy (kilotons of oil or the equivalent) from alternative sources displaced 0.128 and 0.219 units (from the first and second models, respectively) from fossil fuel sources.

These patterns don’t seem to change much over time. In addition, the results are consistent even when considering the varying affluence of different nations—it doesn’t matter if you’re looking at rich or poor nations.

York also looked at the different categories of alternative sources for electricity generation: nuclear, hydro, and non-hydro renewables. Using both models, each kWh of nuclear displaced about 0.2 kWh of fossil fuels, hydro about 0.1, and non-hydro renewables essentially didn’t displace any fossil fuel electricity.

These last results are not surprising. Compared to nuclear plants, which are currently built exclusively to generate electricity, hydropower plants are often constructed for other purposes: flood control, irrigation, etc. On the other hand, the non-hydro renewables like wind and solar haven’t displaced much fossil fuel use because they simply haven’t been deployed significantly yet. Worldwide, these renewables constitute less than four percent of total electricity production.

Based on these results, it’s clear that alternative energy sources have displaced fossil fuels—but just barely. The main takeaway of the study is that if the same pattern of energy use over the past few decades continues into the future, we will need a massive growth of alternative and renewable sources of energy in order to significantly reduce our reliance on fossil fuels.

The most important caveat of this study: the analysis considered only past data, and as such the conclusions may not be relevant for the future. However, these results clearly challenge the assumption that simply developing alternative sources of energy will reduce our use or need for fossil fuels. Without changing the current patterns of energy usage, vastly expanding the adoption of alternative energy sources, or finding a way to make fossil fuels unattractive (York proposes a carbon tax), the pattern of the past will continue.

Nature Climate Change, 2012. DOI: 10.1038/nclimate1451 (About DOIs)