A heated debate in the pages of one of the country’s most renowned scientific journals has gained national attention. The debate is over whether a combination of wind, solar, and hydroelectricity could fully power the U.S. But both sides of the debate are completely missing half of the equation.

In a series of papers published over the last few years, Mark Jacobson of Stanford University (along with co-authors) has offered a series of transition plans for achieving a 100 percent wind-solar-hydro energy economy. These include comprehensive blueprints for the United States, for each individual state, and for the world as a whole. His message is clear: such a transition is not only possible, it’s affordable—cheaper, in fact, than maintaining the current fossil fueled system. There is no technical or economic barrier to an all-renewable future—only a political one, resulting from the enormous influence of fossil fuel companies on Congress and the White House. Jacobson’s plans have been touted by celebrities (Leonardo DiCaprio and Mark Ruffalo) and at least one prominent politician (Bernie Sanders).

However, during the past two years a group of scientists unconvinced by Jacobson’s arguments has labored to craft a critical review of his plans, and to get it published in the same journal that printed Jacobson’s own most-cited paper. They voice a concern that the growing popularity of Jacobson’s plans could lead to critical mistakes in policy making and investment choices. The lead author, Christopher Clack, and his 20 co-authors, attack Jacobson’s assumptions and highlight what they call serious modeling errors. Much of their criticism has to do with Jacobson’s ways of getting around solar and wind power’s most notorious drawback—its intermittency. Jacobson says we can deal with cloudy and windless days by storing energy in the forms of underground heat and hydrogen. Clack et al. point out that doing so on the scale Jacobson is proposing is unprecedented (therefore, we really don’t know if it can be done), and also argue that Jacobson made crucial errors in estimating how much storage would be needed and how much it would cost.

The stakes in this controversy are high enough that the New York Times and other mainstream media have reported on it. One pro-renewables scientist friend of mine despairs not just because of bad press about solar and wind power, but also because the reputation of science itself is taking a beating. If these renowned energy experts can’t agree on whether solar and wind power are capable of powering the future, then what are the implications for the credibility of climate science?

Jacobson and colleagues have published what can only be called a take-no-prisoners rebuttal to Clack et al. In it, they declare that, “The premise and all error claims by Clack et al. . . . about Jacobson et al. . . . are demonstrably false.” In a separate article, Jacobson has dismissed Clack and his co-authors as “nuclear and fossil fuel supporters,” though it’s clear that neither side in this debate is anti-renewables.

However, Clack et al. have issued their own line-by-line response to Jacobson’s line-by-line rebuttal, and it’s fairly devastating.

This is probably a good place to point out that David Fridley, staff scientist in the energy analysis program at Lawrence Berkeley National Laboratories, and I recently published a book, Our Renewable Future, exploring a hypothetical transition to a 100 percent wind-and-solar energy economy. While we don’t say so in the book, we were compelled to write it partly because of our misgivings about Mark Jacobson’s widely publicized plans. We did not attack those plans directly, as Clack et al. have done, but sought instead to provide a more nuanced and realistic view of what a transition to all-renewable energy would involve.

Our exploration of the subject revealed that source intermittency is indeed a serious problem, and solving it becomes more expensive and technically challenging as solar-wind generation approaches 100 percent of all electricity produced. A further challenge is that solar and wind yield electricity, but 80 percent of final energy is currently used in other forms—mostly as liquid and gaseous fuels. Therefore the energy transition will entail enormous changes in the ways we use energy, and some of those changes will be technically difficult and expensive.

Our core realization was that scale is the biggest transition hurdle. This has implications that both Jacobson et al., and Clack et al. largely ignore. Jacobson’s plan, for example, envisions building 100,000 times more hydrogen production capacity than exists today. And the plan’s assumed hydro expansion would require 100 times the flow of the Mississippi River. If, instead, the United States were to aim for an energy system, say, a tenth the size of its current one, then the transition would be far easier to fund and design.

When we start our transition planning by assuming that future Americans will use as much energy as we do now (or even more of it in the case of economic growth), then we have set up conditions that are nearly impossible to design for. And crucially, that conclusion still holds if we add nuclear power (which is expensive and risky) or fossil fuels (which are rapidly depleting) to the mix. The only realistic energy future that David Fridley and I were able to envision is one in which people in currently industrialized countries use far less energy per capita, use it much more efficiently, and use it when it’s available rather than demanding 24/7/365 energy services. That would mean not doing a lot of things we are currently doing (e.g., traveling in commercial aircraft), doing them on a much smaller scale (e.g., getting used to living in smaller spaces and buying fewer consumer products—and ones built to be endlessly repaired), or doing them very differently (e.g., constructing buildings and roads with local natural materials).

If powerdown—that is, focusing at least as much on the demand side of the energy equation as on the supply side—were combined with a deliberate and humanely guided policy of population decline, there would be abundant beneficial side effects. The climate change crisis would be far easier to tackle, as would ongoing loss of biodiversity and the depletion of resources such as fresh water, topsoil, and minerals.

Jacobson has not embraced a powerdown pathway, possibly because he assumes it would not appeal to film stars and politicians. Clack et al. do not discuss it either, mostly because their task at hand is simply to demolish Jacobson. But powerdown, the pathway about which it is seemingly not permissible for serious people to speak, is what we should all be talking about. That’s because it is the most realistic way to get to a sustainable, happy future.

Featured image via Pixabay.