President  Obama walks with John Holdren, assistant to the president for science and technology, at the White House in March 2014. (Win McNamee/Getty Images)

White House science adviser John Holdren’s comment Monday that it was “unrealistic” to halt fossil fuel extraction altogether in the U.S. may have seemed like stating the obvious. But it has further highlighted the tensions that exist even among top American policy makers and environmental advocates concerned about curbing the rate of climate change.

Bernie Sanders and his followers, influential green movement leaders like Bill McKibben and powerful organizations like the Sierra Club, have been pushing a “keep it in the ground” approach. For these advocates, a future strongly dependent on wind, solar  and batteries can’t come fast enough. And they have led campaigns not only to oppose fracking for natural gas but also to block — successfully — the Keystone XL pipeline. Most recently, Sanders’s supporters have been deeply engaged in a push to make the Democratic Party’s official platform more strongly reflective of this point of view, although they were unsuccessful in trying to incorporate a fracking ban into the platform.

Yet Obama administration officials and many energy policy wonks continue to suggest that we will need to rely on burning natural gas, nuclear energy and even outfitting coal plants with carbon capturing technologies for some time. In contrast to “keep it in the ground,” their approach has sometimes been labeled “all of the above.” Meanwhile, Clinton has called natural gas, in particular, a “bridge” to a cleaner energy future.

Sanders’s supporters did score a few victories in the recent platform-writing process by passing amendments endorsing a price on carbon, methane and other greenhouse gases and supporting the rights of local communities to ban fracking. Those “unity amendments” were implicitly backed by  presumptive Democratic nominee Hillary Clinton.

The tension was reawakened yesterday at this week’s annual conference held by the Energy Information Administration. According to a Tweet by Brian Scheid, a reporter for Platts, Holdren yesterday called the “keep it in the ground” movement “unrealistic” in his keynote speech at the conference.

Morning Consult also reported that Holdren stated, “The notion that we’re going to keep it all in the ground is unrealistic. We are still a very heavily fossil-fuel dependent world.”

“When asked whether it was feasible to leave all the remaining fossil fuels in the ground, Dr. Holdren noted that it is not, because the U.S. — and the world — still depend on fossil fuels for more than 80 percent of all the primary energy we use,” said White House spokeswoman Lindsey Geisler said in an email. “It’s not practical or affordable to replace the huge, fossil-fuel infrastructure with nuclear and renewables overnight, no matter how badly we may want to. As a result, the U.S. will be using fossil fuels for decades to come, albeit, one hopes, with the share of non-fossil supplies increasing over time.”

In one sense, Holdren’s remarks could be viewed as simply stating what’s already known. Indeed, wind and solar  provided a little over 5 percent of U.S. electricity last year. Meanwhile, a key driver of the  recent U.S. trend toward  “cleaner” energy has not been burning less fossil fuels, but rather the swapping of one fossil fuel for another.

More specifically, very cheap natural gas prices, which have driven fracking and the exploitation of huge new “unconventional” shale gas reserves, has led to a shift in how we get power. More and more, utility companies are switching away from burning coal for electricity and toward  burning gas. According to the EIA, 2016 is likely to be the first year in which the country as a whole gets more of its electricity from gas than from coal.

And that has significant greenhouse gas emissions implications, as natural gas burns cleaner than coal and only produces about half as much carbon dioxide emissions per unit of energy.

“Facts are  facts: America is leading the world in oil and natural gas production and in lowering carbon emissions, which are at 20-year lows, because of clean-burning natural gas,” said Eric Wohlschlegel, director of media relations and communications at the American Petroleum Institute, regarding the Holdren statement. “American voters support increased oil and natural gas production. They understand that the wind doesn’t always blow and the sun doesn’t always shine and that an all of the above energy strategy is needed to power our future. Keep-it-in-the-ground tactics aimed at misleading the public present a false choice, especially when there’s overwhelming support for American energy production.”

In the transportation sector, meanwhile, cleaner options like electric cars or cars that run on high volumes of biofuels are even further away from achieving market dominance than wind and solar are in the electricity sector. So when Holdren reportedly called the “keep it in the ground” movement “unrealistic,” it was simply a statement that there is no way we are going to get off fossil fuels in the near term.

Still, that stance diverges from that of environmentalist allies. “Science shows clearly that if we want to protect the health of our communities from dangerous pollution and the serious threats of the climate crisis, we have to start keeping dirty fossil fuels in the ground now,” said Michael Brune, the executive director of the Sierra Club, in response to Holdren’s statement. “That clearly means that gas cannot be a bridge fuel, and the Obama Administration’s efforts to mitigate the threat gas posed through methane safeguards and fracking standards shows they recognize the dangers of this pollutant.”

Indeed, top administration officials have emphasized the need to reexamine the climate implications of fossil fuel extraction from federal lands and waters, but have not yet embraced the idea of banning these activities altogether. Interior Secretary Sally Jewell, a former petroleum engineer, has said that government officials need to recognize that some of the nation’s fossil fuels must remain untapped if they are serious about combating global warming, and the department just imposed stricter rules on oil and gas drilling in the Arctic Ocean.

In January Interior put a moratorium on new coal leasing on federal land, arguing it needed to scrutinize both the carbon impact and economic implications of its coal leasing practices in the West.

But several aspects of the department’s energy leasing program have continued under stricter safety standards, including offshore oil and gas leasing in the Gulf of Mexico. Those activities are a major source of revenue for the federal government.