Limiting global warming to less than two degrees Celsius first and foremost requires a rapid worldwide transition from fossil fuels to renewable energy, and a team of scientists led by Stanford University's Mark Z. Jacobsen has developed a clear map for that path.
The team's study, published this week in the the journal Joule, describes how 139 countries, accounting for 99 percent of global greenhouse gas emissions, can power themselves entirely with wind, water, and solar by the year 2050—at a quarter of the overall cost of the current fossil fuel system.
The findings are a stark counterpoint to a contentious United States Department of Energy report released the same day that hems and haws about renewables while seeking to boost support for coal and nuclear energy.
The Trump administration may want to boost fossil fuels for political reasons, but science clearly shows that a swift transition to renewables is in the best interest of the U.S. and the rest of the world, the authors say—adding that most people aren't hearing regularly about what real solutions would look like.
"Policymakers and civil society need guidance on the options from visionary people with the capabilities of suggesting realistic pathways for a sustainable future," says Finnish renewable energy researcher Christian Breyer, who was not involved in the study. Existing institutions are propping up fossil fuels "while our planet burns," he says. "The more details are shown, the more people can be convinced that a 100 percent renewable energy pathway is the solution."
The energy transition could also create up to 24 million long-term jobs and would prevent four million to seven million premature air pollution deaths while saving more than $20 trillion in health-care costs annually. With good governance, Jacobsen's team has found, the renewable system could be built at a similar cost to a business-as-usual energy pathway.
Eliminating oil, gas, and uranium from the future mix of energy sources cuts the amount of energy needed to mine, transport, and refine those fuels by 13 percent, while widespread electrification would have a dampening feedback effect on energy demand, because electricity is much more efficient at producing power than direct combustion of fossil fuels; for example, in transportation, an electric car can travel farther per unit of energy than a gas-powered vehicle.
These changes in infrastructure would also mean that countries wouldn't need to depend on one another for fossil fuels, reducing the frequency of international conflict over energy.
All in all, the public benefits of clean energy are significant, especially in countries that currently take the brunt of climate impacts despite having emitted fewer greenhouse gases historically, says co-author Mark Delucchi, who calculated the cost-benefit ratios in the study. The findings suggest that transitioning to wind, water, and solar is so cost-effective that countries should be "retiring fossil fuel systems early wherever we can," he says.
The transition can be achieved with existing technologies, without disrupting energy transmission grids, and without using nuclear energy or carbon capture and storage. The only obstacles are social, cultural, and political; science-based governance can help communities benefit from the accelerating global energy shift, according to Jacobsen, who says the rate of current renewable energy deployment must increase a hundredfold to meet the goals of the Paris Agreement.
Co-author Delucchi says critiques of the previous papers that used similar methodology raise legitimate questions that should be widely discussed—for example, how to evaluate the costs of greenhouse gas pollution, especially in terms of human lives.
Delucchi says he's reasonably confident that 80 to 90 percent decarbonization with wind, water, and solar is within reach by 2050. For the last 10 percent, he says, it may be worth starting to consider other options like nuclear and carbon capture.
But triggering the shift on the scale needed to meet goals of the Paris climate agreement is not going to happen without some government involvement to ensure that the public benefits of the energy transition are reflected in the marketplace.
Delucchi says that, until recently, experts advocating for vigorous governance were somewhat sidelined, while free-market advocates dominated the debate with their claims that a broad carbon tax would be enough to regulate the market.
"What I like to say to people who say we need a carbon tax is, 'We didn't get the interstate highway system by putting a tax on horse manure,'" Delucchi says. "You have to have some other vision."