America needs clean electricity. These states show how to do it.

If humans escape climate scientists’ gloomiest projections, if we buy ourselves time to adapt to higher seas and fiercer heat waves, we will likely use more electricity than we do now, and we will make it without emitting greenhouse gases.

Today, the United States is running a natural experiment in electricity generation, with a patchwork of policies and power grids. To eliminate electricity’s greenhouse gas emissions, it makes sense to ask: What can we learn from the states that make cleanest power?

The chart below shows how the United States has made electricity for the past twenty years, represented as the percentage of power generated from each fuel source. To show how their relative usage has shifted, the fuels are stacked each year from top to bottom in order of percentage.

At this rate, the United States might never completely decarbonize its electricity. In a future where global warming is more mild than catastrophic, we will need to change how we make electricity.

To search for ideas about how to decarbonize electricity, let’s turn to the states with the lowest carbon intensity. To be clear, electricity generated in one state is often exported to others, so we will only show electricity generation, not consumption. As you can see in the charts below, these six states make a lot of electricity with hydroelectric dams and nuclear power plants.

Hydroelectric dams have “a history of flooding tribal lands, devastating fish populations, and disrupting many beneficial functions of rivers,” Bill Corcoran, the director for the Sierra Club’s Beyond Coal Campaign, told me in an email.

Due in part to environmental opposition, the United States has not begun construction on a major hydroelectric dam since the 1970s. The Sierra Club and other big environmental groups are open to adding generators to existing dams, but that would not significantly boost the supply of carbon-free power.

In Washington state, which gets about two-thirds of its power from hydroelectricity, groups like the League of Conservation Voters want to remove hydroelectric dams on the Snake River to protect endangered salmon. Some dams, such as the Colorado River’s Glen Canyon Dam, are threatened by overuse and drought, a risk factor made worse by climate change.

The biggest obstacle to building new nuclear plants is their cost. Construction on the last nuclear reactors built in the United States, at Georgia’s Vogtle Electric Generating Plant, is six years behind schedule, $14 billion over budget, and contributed to bankrupting Westinghouse. The debacle has become a cautionary tale to would-be nuclear developers.

“If you don’t have something to lower the cost or in some way incentivize nuclear, I don’t see much hope for it in the U.S., which is too bad, because from my perspective, it’s a fantastic option in a decarbonized world,” Jennifer Faye Morris, principal research scientist at the MIT Energy Initiative, told me.

Nuclear supporters are optimistic about the Biden administration’s recent bailout of financially strapped nuclear plants and its backing of next-generation technologies like small modular reactors. Yet it will be many years before those technologies could be widely deployed — the nation’s first small modular reactor just received a crucial design certification early this year.

Many environmental groups, already concerned with the country’s lack of a long-term waste repository and the prospect of catastrophic meltdowns (no one has died from radiation at a commercial nuclear plant in the United States), have seized on nuclear’s economic troubles.

“The entire nuclear industry has become an overpriced distraction,” said Lukas Ross, climate and energy program manager at Friends of the Earth.

In short, most major environmental groups oppose the two technologies that have historically generated carbon-free electricity. Instead, they have turned their hopes to other clean fuels: wind and solar.

Wind power and the electric superhighway

Of those two, wind power has enjoyed the most growth in recent years, expanding from a negligible amount of generation in 2000 to 8 percent of the nation’s electricity in 2020. The Inflation Reduction Act, which passed last year with $369 billion in climate- and energy-related funding, included tax incentives for wind power, which should further boost its growth.

Iowa now generates most of its electricity from wind farms, more than enough to export to other states. As a result, it slashed its carbon intensity from electricity generation more than any other state between 2000 and 2020.

The other states in the top six all have two things in common with Iowa: a lot of land and a lot of wind. States with similar qualities, like Texas, Montana, New Mexico and Wyoming, could better exploit their untapped wind power.

On the heavily populated coasts, where land and windiness are in relatively short supply, the potential is more limited. Powering the coasts with the midwest’s wind would mean building new, long-distance transmission lines. This so-called “electric superhighway” is, like most major infrastructure projects, easier to imagine than to build.

“There’s not many long-distance transmissions lines because they’re expensive and can be difficult to site,” said Glenn McGrath, a power systems analyst at EIA. “Building such a line requires approval of land managers and stakeholders, and if you have a long way to go, you can imagine that that would be quite a project.”

Long-distance transmission lines have met with mixed success. A proposed line to transmit hydroelectric power from Quebec to Massachusetts was shut down in 2018 after New Hampshire denied it a permit to run through the state. Seeking to avoid similar problems, the developer of a $2.5 billion project that would transmit wind power from Iowa to Illinois plans to bury the lines underground along a railroad.

Solar panels in a battery-powered future

Like wind, solar power has enjoyed a growth spurt, encouraged by declining prices and favorable government policies. Stimulated by the Inflation Reduction Act, U.S. solar capacity is projected to double over the next five years.

Yet solar’s growth has been slow.

Even California, a sunny state with supportive policies, generated just 16 percent of its electricity from solar in 2020. Sun-drenched states in the southwest have room to grow, but solar’s potential in northeastern states like Vermont and Massachusetts is limited. Even in sunny states, solar panels sit idle at night.

Energy experts who support expanding solar — and its cousin, wind — worry about their ability to provide a major share of the country’s electricity needs.

“Wind and solar are very cheap. They give you zero carbon electricity,” Michael Craig, assistant professor in energy systems at the University of Michigan, told me. “But some times of the year, and some years even, you need something other than wind and solar because you don’t have power from them. And so you get it from somewhere else.”

In practice, electric grids with lots of wind and solar, such as those in California and Massachusetts, often rely on carbon-emitting natural gas plants that can quickly ramp up generation to fill in the gaps.

Supporters of wind and solar say battery storage will help balance out the intermittency. The Sierra Club’s Corcoran told me that batteries and other technologies “will reduce the ‘spikiness’ of peak demands for energy,” thus stabilizing the grid.

Large-scale battery capacity grew rapidly over the last decade as costs fell and demand increased. Yet projections suggest battery storage will remain a fraction of power supply for years to come.

Connecting solar and wind to the grid has also posed technical hurdles for some transmission authorities, resulting in long waiting lists to connect. In some places, such as Marion County, Ohio, and Rotterdam, N.Y., local governments have voted against developing new large solar and wind projects.

The natural gas swap

Abundant natural gas deserves much of the credit for weaning the United States off coal. Between 2005 and 2018, replacing coal with natural gas drove a larger reduction in carbon dioxide emissions than replacing coal with zero-carbon sources like wind and solar.

Natural gas is cleaner than coal, but is it clean? Let’s compare the three states with the largest share of electricity generation from coal versus the three with the largest share from natural gas.

Carbon intensity in the natural gas states — Rhode Island, Delaware and Mississippi — is lower than in the coal states but higher than the national average. If the goal were to reduce carbon dioxide emissions, natural gas would help. For many, the goal is to eliminate emissions.

Enter carbon capture and storage, a technology that removes carbon from burnt fuel’s emissions and stores it underground or beneath the ocean. Supporters tout its potential to slash emissions without abandoning the fossil fuels upon which modern life depends. For now, the technology is expensive, unable to capture enough carbon and rarely used.

By now, it should be clear that making electricity without emitting carbon dioxide is no small feat. Below, you can check the carbon intensity and fuel mix of the 50 states and Washington, D.C.

The charts in this article were inspired by designs created by Nadja Popovich of the New York Times. I modified the design to include the carbon intensity of the fuel mix. Nadja tells me she was inspired by a similar design by Gregor Aisch, who you may know as the creator of Datawrapper. We all stand on the shoulders of giants.

If you have ideas on how the United States should make its electricity, I’d love to hear them. Email me at harry.stevens@washpost.com.