Describing how totalitarian regimes create revisionist histories to justify new and often sweeping social and political arrangements, George Orwell famously wrote, “Who controls the past controls the future; who controls the present controls the past.” But in today’s aspirational democracies, Orwell’s maxim is often inverted: who controls the future controls the present.

Nowhere has this been more the case than in contemporary debates about energy and the environment. Over a half century ago, nuclear advocates promoted a future in which nuclear energy would be too cheap to meter. In the three decades that followed, the United States and other advanced developed economies embarked on a massive build out of nuclear power plants. For almost as long, renewable energy advocates have promised a hyper-efficient future powered entirely by the sun and the wind, and in recent decades nations around the world have invested hundreds of billions of dollars to make that future a reality.

Both visions proved prescient in some ways. At its peak, the global nuclear fleet generated 18 percent of global electricity and over 20 percent of electricity in the United States. France proved that nuclear energy was capable of both powering a modern economy and decarbonizing its power sector. And although it never became too cheap to meter, over the operational lifetime of nuclear plants, the full cost of generating nuclear electricity did prove to be remarkably low.

Modern economies around the world have also become much more energy efficient, and the cost of manufacturing wind turbines and solar panels has fallen precipitously with sustained deployment, as renewable energy advocates predicted.

Fences and fields are covered with frost near the A6 highway, also known as the "Autoroute du Soleil (Highway of the Sun) near Dijon, France January 6, 2015. Yves Herman / Reuters But it is also true that neither vision has come close to delivering on its promise. Few developed economies are building new nuclear reactors. And although a nuclear renaissance is well and truly underway in the developing world, the build out of fossil energy infrastructure in developing nations is proceeding even faster. Concerted efforts to deploy solar and wind energy in various locales around the world, meanwhile, have failed to push wind and solar much beyond 20 percent of total annual generation on any large electrical grid.

Energy futures, it turns out, are not so easily bent to utopian dreams. And yet, we continue to propose them, to argue about them, and to find others to blame when they fail to materialize. The reasons for this are easy enough to see. The present is complicated and consequential. The future, by contrast, is shining, weightless, and perfectly optimized: a place where trade-offs are unnecessary and constraints can be assumed away.

IN THE FORECAST

The business of forecasting and modeling energy futures exploded after the Arab oil embargoes of the 1970s. The range of futures that studies from that era imagined is truly head-spinning. But the one feature that they shared was that they reliably failed to anticipate the future. Mainstream forecasts from the 1970s and 1980s consistently overestimated both future energy demand and the expansion of nuclear energy.

Amory Lovins and other renewable energy prognosticators of that era were sometimes closer to the mark in terms of energy demand. But they were wildly off in their projections of renewable and decentralized energy. And even their demand forecasts were right for the wrong reasons. Lovins claimed that dramatic improvements in energy efficiency would result in lower energy consumption. But slower economic growth, deindustrialization, and sectoral shifts in the U.S. economy are what mostly accounted for slower demand growth.

With the advent of international efforts to address climate change, the predominance of models, scenarios, forecasts, and feasibility studies in discussions about energy and environmental futures has only grown. With that the opportunities to introduce all manner of error, bias, and delusion have grown as well, all done with a sheen of mathematical precision and scientific authority.

In 2009, a hitherto obscure civil and environmental engineering professor from Stanford University named Mark Jacobson rose to prominence as Lovins’ heir apparent. With a colleague, Jacobson published a plan in Scientific American to power the entire U.S. economy with wind, water, and solar energy. Money followed notoriety, and in 2011, Jacobson launched the Solutions Project, which today claims to have demonstrated that all 50 states and 193 countries can be powered solely with renewable energy.

Like Lovins before him, Jacobson’s claims and calculations have been embraced by environmental NGOs, for whom his models provide justification for long-standing opposition to nuclear energy, hydropower, and more recently, natural gas. His roadmaps for each of the 50 states were literally embedded into the climate and energy section of Senator Bernie Sanders’ website.

Even by Lovins’ lofty standard, Jacobson’s projections are audacious. Like Jacobson, Lovins’ scenarios lean heavily on radical gains in energy efficiency. But Lovins made at least a few concessions to the limitations that wind and solar energy face, calling for small, super-efficient micro coal plants and even in-home natural gas turbines to keep the system going.

Lovins also recognized that profound transformation of the American energy economy would take time. His vision, radical as it was, only envisioned that about a third of the U.S. electrical grid would be powered by wind and solar energy in the year 2000. As it happened, the actual percentage was .5 percent.

Jacobson, by contrast, claims that the entire global economy can be run on intermittent renewable energy technologies by 2050. To do so, he summons all sorts of technology from the future, including geothermal energy storage, to heat and cool all residential and commercial buildings, phase change batteries, and hydrogen powered airplanes, even as he claims that his scenario is based entirely upon existing technologies. He further envisions the creation of an electrical grid on steroids, double or more the size of the current system, in order to electrify transportation and other energy-intensive sectors of the economy, and capable of transmitting huge amounts of electricity across continents and oceans, in order to balance out and synchronize highly variable wind and solar resources.

Details aside, it is important to understand what a profound transformation a renewable-dominated future of this sort would represent. Energy systems are highly path dependent and are embedded in broader techno-economic paradigms. The rise of coal cannot be disentangled from the steam engine, railroads, and electricity. The age of oil is inseparable from the internal combustion engine, modern transportation networks, and urbanization. Centralized electrical grids coevolved with modern cities and industry.

As modern economies grew in scale over the last century or so, they have become increasingly centralized, as have the energy systems that powered them. Prior to the industrial revolution, all energy systems were distributed, decentralized, diffuse, and renewable. Early electrical systems were small scale, and competing providers offered patchwork service to the few businesses and residences able to afford it. The centralized grid and regulated utility were the killer apps that allowed electricity to transform manufacturing, industry, and ultimately urban life in the first decades of the twentieth century.

A tower belonging to the Abengoa Solar plant is seen at the "Solucar" solar park in Sanlucar la Mayor, near the Andalusian capital of Seville, southern Spain November 30, 2015. Marcelo del Pozo / Reuters Dense fossil fuels and increasingly efficient combustion and end use technologies have continued to make modern energy services ever cheaper, more abundant, and increasingly accessible to more people and more sectors of the economy. For these reasons, for the better part of two centuries, the long-term evolution of energy systems has been towards denser fuels and more centralized power generation and distribution.

The story of energy transitions is inseparable from the new end uses and radical new production efficiencies those transitions enable. Within a decade or so of Edison’s first electrical generating station at Pearl Street, the transformative power of electrification for transit and manufacturing was already clear. A decade later, the regulated monopoly utility was born and the electric age came into being. The superior speed, range, and hauling capacity of railroads and then automobiles similarly drove the rapid build out of public and private infrastructure to take advantage of them.

In more recent times, the benefits of new fuels and energy technologies have been less radical, which perhaps explains how durable the basic arrangements of our fossil-fueled energy infrastructure have been. Natural gas initially found purchase due to its superior qualities as a heating and cooking fuel. In recent decades, radical improvements in gas turbine design made gas a more versatile and flexible fuel for electricity generation, assuring it a growing role in the power sector even before gas prices hit rock bottom thanks to the shale revolution. The rapid displacement of coal with gas in the United States over the last decade owes not only to the fact that it was so cheap but also to the fact that it could also basically plug and play with the existing centralized power grid. Despite their technological novelty and complexity, nuclear reactors can similarly plug and play with the existing, centralized power grid and hence have proven capable of displacing centralized fossil energy generation at a large scale.

Of course, these are the arrangements that Lovins, Jacobson, and many other renewable energy advocates have, for half a century, insisted are coming to an end. Soon enough, they argue, the world will be powered entirely by diffuse sources of energy, collected over vast swaths of the planet, transmitted over enormous distances, and distributed in decentralized fashion. And the truth is, nobody exactly can prove that such a future is improbable, for the simple reason that the proof, one way or another, lies in the future.

But there are good reasons to think that there will be real limitations to how much wind and solar energy we will be able to utilize. Much has been made of the positive scaling factors associated with wind and solar energy. The cost of solar modules and wind turbines falls as production scales up. But there is also a negative scaling factor associated with variable renewable energy technologies that has been much less discussed. The cost of integrating those resources into electrical grids rises as their share of total electricity increases.

Wind and solar energy are plagued by very low capacity factors. Capacity factor is the measure of how much electricity a power plant produces annually in relation to how much electricity it would produce if it operated 24 hours a day, 365 days a year. Coal plants typically have capacity factors above 60 percent, whereas nuclear plants routinely exceed 90 percent. Wind farms, by contrast, typically have capacity factors around 30 percent, and the best solar farms have a capacity factor of around 20 percent.

Because the capacity factors associated with wind and solar generation are so low, once the share of wind and solar generation starts to approach about 20 percent of total electricity demand, the value of those resources collapses. Wind and solar in these circumstances routinely produce more energy than the grid requires at certain times of day, necessitating the curtailment of electrical production from either renewable resources or nuclear and fossil resources. In either event, costly capital equipment goes unutilized, increasing the total system cost of delivering reliable electricity to users year round.

You can’t simply get rid of fossil and nuclear generation to solve this problem. When the wind isn’t blowing and the sun isn’t shining, you still need to meet electricity demand. Whenever some locale with high renewables penetrations—Texas or Germany or Denmark—is able to meet its entire demand for electricity with renewable energy, usually on a particularly clear and windy weekend day when electricity demand is low, we hear about it. Little noted are the days and sometimes weeks at a time when wind and solar generation fall to zero. Achieving very high shares of wind and solar electricity requires not only daily storage but also storage of vast quantities of electricity over weeks and months to account for seasonal variation.

For these (among other) reasons, extraordinary measures are still necessary to sustain renewables growth, even at the relatively low levels of penetration that they have achieved today and despite precipitous declines in the cost of manufacturing turbines and panels that has occurred over the last several decades. In a variety of ways—tax credits and feed-in tariffs, deployment mandates and merit order rules, capacity markets and net metering policies, to name a few—the full cost of increasing dependence on variable renewables is externalized to other stakeholders, meaning taxpayers, ratepayers, utilities, and other generators.

Those costs have been manageable at low levels of deployment. But as deployment increases, so do costs. Spain, Italy, Japan, and even Germany have scaled back renewables subsidies and slowed deployment in the face of mounting expense. Even continuing and dramatic declines in the costs of panels and turbines are unlikely to solve this problem. “Even if you give away the [photovoltaic] materials for free,” the author of a recent MIT study on the future of solar energy told the MIT Technology Review, “you still couldn’t produce electricity as cheaply as with coal or natural gas.”

None of this means that solar, wind, and other sorts of renewable energy might not play an important role in our energy future. But it does mean that we are unlikely to approach 100 percent renewable energy, or anything close to it, as Jacobson and other prophets of the renewables revolution have suggested. Deeply decarbonizing the global economy will require other zero carbon technologies as well.

A man walks next to solar panels at a soon-to-be completed solucar solar park at Sanlucar La Mayor, near Seville, February 13, 2008. Marcelo del Pozo / Reuters THE FUTURE THIS TIME

If the last half-century of failed energy prognostication should temper enthusiasm for sweeping energy visions of all sorts, it is also true that meaningful mitigation of climate change will require a transformation of the global energy economy at an unprecedented scale and pace. And although there remains enormous uncertainty about the future of the global economy and of energy technologies, there is much that we can learn from both the failure of past energy forecasts and the long-term evolution of the global energy system that might help us better plan for the future and mitigate climate change.

Start with the likelihood that, although we can’t know the exact magnitude, global energy demand is likely to grow for a very long time and to stay very high for much longer. This is just simple demographics and economics. Under the best of circumstances, the global population will stabilize at around nine billion people at some point in the middle of this century. Most of those people are very poor today and don’t consume much energy. So it is a safe bet that a larger population will continue to pursue better living standards, and in the process of achieving those standards, will consume more energy, even with continuing improvements in efficiency.

As such, future energy and decarbonization scenarios that assume that global energy demand will be flat over the coming decades should be viewed with a fair degree of skepticism. The scale of low-carbon energy infrastructure that will need to be deployed to meet growing demand and replace existing fossil infrastructure is enormous and won’t be wished away through clever modeling assumptions.

A second important lesson is that we don’t know the technological future and should not over-commit to any given low-carbon pathway. While renewables and nuclear advocates spent the 1980s and 1990s arguing about which technology represented the future, an obscure collection of oil and gas entrepreneurs and federal scientists were quietly working to figure out how to economically extract gas from shale formations.

Few people, even within the oil and gas industry, thought that shale gas would ever be economically recoverable. Federal support for shale research and development was a tiny part of the federal non-conventional fuels budget, much of which was spent on synthetic fuels and oil shales, which most people thought more promising.

If there is one lesson from the shale revolution, it is that we need to pursue an energy policy that is robust to a range of possible technological futures. In some cases, that will entail shifting toward technologically neutral policies. A price on carbon, for instance, would help all low-carbon technologies. And the time is long overdue to turn renewable portfolio standards into zero-carbon standards. But it is also the case that there would be no shale revolution, no commercial nuclear energy technology, and no wind or solar energy industry without sustained and targeted technology policies.

A mix of technology neutral policies to tilt the playing field toward zero carbon energy, a broad portfolio of technology specific policies to help develop and deploy the key technologies we will need to get to zero, and smaller bets on longer-term but potentially game-changing technologies will be the best way to hedge our technology bets.

Two Google engineers, in their requiem for Google’s RE<C (Renewable Energy Cheaper than Coal) effort described this approach as 70/20/10, with 70 percent of expenditures going toward deploying existing low carbon technologies like solar photovoltaics and light water reactors, 20 percent toward next generation technologies such as advanced nuclear fission and thin-film solar technology, and ten percent toward moonshot type bets like nuclear fusion and space-based solar power.

But more than any particular set of assumptions or policies, what we will need to move forward in a pragmatic way to address our energy and climate challenges will not be better analysis or models but a better public spirit. Like so many intractable political debates, most of our disputes about energy and climate change can be traced back to the social and political discord that tore the country apart in the 1960s. The idea that we might power the world with localized and decentralized renewable energy was borne of a broader vision about how society might be transformed into a more humane, more manageable, and more equitable place. Over the course of that decade, nuclear energy came to be seen by many on the Left as antithetical to those aspirations—“an alien, remote, and perhaps humiliatingly uncontrollable technology run by a faraway, bureaucratized, technical elite” as Lovins memorably put in his seminal 1977 Foreign Affairs article.

This history should remind us that our ideas about energy futures are almost always proxies for our values, and, too often, we have ended up fetishizing particular technologies and losing track of our ideals. Jacobson’s models, calling for continent-spanning electrical grids and thousands of enormous industrial scale wind and solar farms, suggest that a world powered entirely by wind, water, and solar energy will be one that is no less remote, industrial, large-scale, and centralized than the nuclear future that Lovins and his peers rejected. And if the promise of small advanced nuclear reactors is realized, the world might be powered with exactly the sorts of decentralized and distributed technologies that Lovins and others imagined.

Faced with great global challenges, a growing population (most of which will need to consume more energy), and a climate that needs that energy to be zero carbon, we would all be well advised to check our technological priors at the door and ask ourselves what things we really care about. A prosperous and equitable world, a low carbon future, and a manageable and accountable energy system are all possible. To get there, we will need better renewable and better nuclear energy technologies. And both sides of the nuclear/renewable debate will need to abandon their decades old feud and work together to deploy both nuclear and renewable energy as fast as we can.