Meet Vaclav Smil, the man who has quietly shaped how the world thinks about energy

With the exception of Germany.

As a teenager in the 1950s, Vaclav Smil spent a lot of time chopping wood. He lived with his family in a remote town in what was then Czechoslovakia, nestled in the mountainous Bohemian Forest. On walks he could see the Hohenbogen, a high ridge in neighboring West Germany; less visible was the minefield designed to prevent Czechs from escaping across the border. Then it was back home, splitting logs every 4 hours to stoke the three stoves in his home, one downstairs and two up. Thunk. With each stroke his body, fueled by goulash and grain, helped free the sun's energy, transiently captured in the logs. Thunk. It was repetitive and tough work. Thunk. It was clear to Smil that this was hardly an efficient way to live.

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Now, as the world faces the daunting challenge of trying to curb climate change by weaning itself from fossil fuels, Smil's work on energy transitions is getting more attention than ever. But his message is not necessarily one of hope. Smil has forced climate advocates to reckon with the vast inertia sustaining the modern world's dependence on fossil fuels, and to question many of the rosy assumptions underlying scenarios for a rapid shift to alternatives. "He's a slayer of bullshit," says David Keith, an energy and climate scientist at Harvard University.

Give Smil 5 minutes and he'll pick apart one cherished scenario after another. Germany's solar revolution as an example for the world to follow? An extraordinarily inefficient approach, given how little sunlight the country receives, that hasn't reduced that nation's reliance on fossil fuels. Electric semitrailers? Good for little more than hauling the weight of their own batteries. Wind turbines as the embodiment of a low-carbon future? Heavy equipment powered by oil had to dig their foundations, Smil notes, and kilns fired with natural gas baked the concrete. And their steel towers, gleaming in the sun? Forged with coal.

"There's a lot of hopey-feely going on in the energy policy community," says David Victor, an expert on international climate policy at the University of California, San Diego. And Smil "revels in the capability to show those falsehoods."

But Smil is not simply a naysayer. He accepts the sobering reality of climate change—though he is dubious of much climate modeling—and believes we need to reduce our reliance on fossil fuels. He has tried to reduce his own carbon footprint, building an energy-efficient home and adopting a mostly vegetarian diet. He sees his academic work as offering a cleareyed, realistic assessment of the challenges ahead—not as a justification for inaction. And he says he has no ax to grind. "I have never been wrong on these major energy and environmental issues," he says, "because I have nothing to sell."

Despite Smil's reach—some of the world's most powerful banks and bureaucrats routinely ask for his advice—he has remained intensely private. Other experts tap dance for attention and pursue TED talks. But Smil is a throwback, largely letting his books speak for themselves. He loathes speaking to the press (and opened up to Science only out of a sense of duty to The MIT Press, his longtime publisher). "I really don't think I have anything special to say," he says. "It's out there if you want to know it."

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In essence, Smil says, humanity has experienced three major energy transitions and is now struggling to kick off a fourth. First was the mastery of fire, which allowed us to liberate energy from the sun by burning plants. Second came farming, which converted and concentrated solar energy into food, freeing people for pursuits other than sustenance. During that second era, which ended just a few centuries ago, farm animals and larger human populations also supplied energy, in the form of muscle power. Third came industrialization and, with it, the rise of fossil fuels. Coal, oil, and natural gas each, in turn, rose to prominence, and energy production became the domain of machines, as such coal-fired power plants.

Now, Smil says, the world faces its fourth energy transition: a move to energy sources that do not emit carbon dioxide, and a return to relying on the sun's current energy flows, instead of those trapped millions of years ago in deposits of coal, oil, and natural gas.

The fourth transition is unlike the first three, however. Historically, Smil notes, humans have typically traded relatively weak, unwieldy energy sources for those that pack a more concentrated punch. The wood he cut to heat his boyhood home, for example, took a lot of land area to grow, and a single log produced relatively little energy when burned. Wood and other biomass fuels have relatively low "power density," Smil says. In contrast, the coal and oil that heated his later dwellings have higher power densities, because they produce more energy per gram and are extracted from relatively compact deposits. But now, the world is seeking to climb back down the power density ladder, from highly concentrated fossil fuels to more dispersed renewable sources, such as biofuel crops, solar parks, and wind farms. (Smil notes that nuclear power, which he deems a "successful failure" after its rushed, and now stalled, deployment, is the exception walking down the density ladder: It is dense in power, yet often deemed too costly or risky in its current form.)

Down the density ladder

In the past, humanity has typically adopted energy sources that have greater "power density," packing more punch per gram and requiring less land to produce. Renewables (green), however, are lower in density than fossil fuels (brown). That means a move to renewables could vastly increase the world's energy production footprint, barring a vast expansion of nuclear power.

One troubling implication of that density reversal, Smil notes, is that in a future powered by renewable energy, society might have to devote 100 or even 1000 times more land area to energy production than today. That shift, he says, could have enormous negative impacts on agriculture, biodiversity, and environmental quality.

To see other difficulties associated with that transition, Smil says, look no further than Germany. In 2000, fossil fuels provided 84% of Germany's energy. Then the country embarked on a historic campaign, building 90 gigawatts of renewable power capacity, enough to match its existing electricity generation. But because Germany sees the sun only 10% of the time, the country is as hooked as ever on fossil fuels: In 2017, they still supplied 80% of its energy. "True German engineering," Smil says dryly. The nation doubled its hypothetical capacity to create electricity but has gotten minimal environmental benefit. Solar can work great, Smil says, but is best where the sun shines a great deal.

Perhaps the most depressing implication of Smil's work, however, is how long making the fourth transition might take. Time and again he points back to history to note that energy transitions are slow, painstaking, and hard to predict. And existing technologies have a lot of inertia. The first tractor appeared in the late 1800s, he might say, but the use of horses in U.S. farming didn't peak until 1915—and continued into the 1960s.

Fossil fuels have similar inertia, he argues. Today, coal, oil, and natural gas still supply 90% of the world's primary energy (a measure that includes electricity and other types of energy used in industry, transportation, farming, and much else). Smil notes that the share was actually lower in 2000, when hydropower and nuclear energy made up more of the mix. Since then, "we have been increasing our global dependence on fossil fuels. Not decreasing," he says.

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