In January the World Wildlife Fund released a report asserting that Indonesia, Madagascar, Mexico, Morocco, South Africa, Turkey, and the Indian state of Madhya Pradesh could meet 100 percent of their projected electricity needs in 2050 by installing solar photovoltaic power plants on less than one percent of their total land area. Which would be excellent news if all anyone needed to make electricity was land and sunshine.

In January the World Wildlife Fund released a report asserting that Indonesia, Madagascar, Mexico, Morocco, South Africa, Turkey, and the Indian state of Madhya Pradesh could meet 100 percent of their projected electricity needs in 2050 by installing solar photovoltaic power plants on less than one percent of their total land area. Which would be excellent news if all anyone needed to make electricity was land and sunshine. Unfortunately, the WWF has let fantasy overtake reality in its dream of an all-renewables future.

Never mind the challenges of obtaining and assembling the materials for a project of this scale. Never mind the infrastructure required for transmitting solar electricity to all who need it, and storing some for a rainy day. Never mind that the report was co-written by three solar power companies. The problem is that this report is a dream, rather than a plan. It is written by visionaries, in a world that desperately needs actionaries.

When renewable energy experts get together, they tend to rhapsodize about the possibilities, believing that this will somehow inspire others to make their visions come true. But ambitious plans to power entire countries on solar energy (or wind or nuclear power, for that matter) don’t have a snowball’s chance in Australia. Such schemes are doomed to fail, and not because of the economic “reality” or the political “reality” — however daunting those may be. They are doomed because of the physical reality: It’s simply not physically possible for the world’s human population to continue growing in numbers, affluence, and energy consumption without trashing the planet.

Reality is a buzzkill. So perhaps it’s no wonder that many otherwise reasonable people have fallen victim to utopian visions of a world free of poverty, hunger, and climate-altering air pollution — all thanks to (insert “clean” energy technology of your choice here). The numbers, however, just don’t add up. Pretending otherwise merely guarantees future disillusionment.

We simply don’t have an alternative to fossil fuels that can be rapidly scaled up, doesn’t require a daunting input of raw materials and energy, and has a relatively low output of air-polluting emissions. As Derek Abbott has reported elsewhere in the Bulletin, nuclear power is not globally scalable because of the limited availability of the relatively scarce metals used to construct reactor vessels and cores, which appears to be a harder limit than the supply of uranium fuel.

Experts who have considered the difficulty of powering the world without fossil fuels or nuclear power have come up with mind-blowing numbers. In an article published in Scientific American in 2009, engineer Mark Z. Jacobson and research scientist Mark A. Delucchi tallied up what it would take to power the whole planet on renewable energy alone by 2030: billions of rooftop photovoltaic systems, millions of jumbo-size wind turbines, hundreds of thousands of wave devices and tidal turbines, tens of thousands of concentrated solar power plants and photovoltaic plants, thousands of geothermal plants, and hundreds of hydroelectric dams. But the construction work doesn’t end there, because population and living standards are expected to continue rising after 2030. At best, such a plan simply kicks the can down the road.

Lately it is physicists — better known for their heady talk about time travel and multiple universes — who are providing a reality check on energy. These are the people, after all, who study the physical world.

Take solar power, for example: It’s appealing because it seems virtually limitless. In only one hour, the sun delivers as much energy to Earth’s surface as humanity consumes in a year. This apparent abundance is deceptive, though. In his “Do the Math” blog, astrophysicist Tom Murphy calculates that, even with an annual energy growth rate of only 2.3 percent, a civilization powered by solar energy would have to cover every square inch of Earth’s land area with 100-percent-efficient solar panels within a few hundred years. Even if we covered the oceans too, and surrounded the sun and other nearby stars with solar panels, eventually there would not be enough energy in the galaxy to meet the growing demand. Yet many energy experts treat growth as a given, focusing only on which technology can best satisfy the insatiable demand.

While it’s theoretically possible to power an entire society on renewable energy, that certainly wouldn’t be cheap or painless, and any solution would only be a temporary one. Replacing fossil fuels is a wicked problem, and it doesn’t help when researchers and environmental groups try to make it sound easy.

There’s another way to approach the problem: start with supply instead of demand, and work backward from there. In his book Sustainable Energy — Without the Hot Air, physicist David J.C. MacKay calculates how much energy could sustainably be produced in the United Kingdom with a massive expansion of existing technology. The total turns out to be less than the nation’s energy consumption, which suggests to MacKay that the only path forward is to reduce demand — through energy efficiency improvements, for example — until it balances with supply.

Renewable energy advocates typically support conservation efforts, but they don’t make reducing consumption their primary goal. Panicked by the urgency of the climate crisis, and rightfully so, their knee-jerk response is a “just do it” approach to technology. “Why don’t we just build more solar panels and wind turbines?” they ask.

To which I say: Why don’t we just not do it? Let’s not build any new power plants except to replace old, inefficient ones. Let’s not dig up all the oil. Let’s not drive to work alone. Let’s not eat meat every day. Let’s not turn the thermostat up so high. Let’s not buy so many things we don’t really need. And above all, let’s not accept continued energy growth as a necessary or even desirable way of life.