During the first Clinton-Trump presidential debate on Sept. 26, Hillary Clinton accused Trump of believing that "climate change is a hoax perpetrated by the Chinese," and Trump interrupted to object. (The Washington Post)

This story has been updated.

You haven’t heard it much in the media, but this election is likely to have large consequences for how the United States, and perhaps the world, addresses climate change. And that is simply because the candidates’ positions contrast sharply on the matter, and because the world has begun an ambitious emissions reduction regime under the Paris climate accord that only one of the candidates wants to continue.

Donald Trump, in an interview with the Washington Post’s editorial board in March, said he is “not a big believer in man-made climate change.” And Trump has said that if elected he would “cancel” the Paris climate agreement – which enters into force on Friday, Nov 4. He has also stood up strongly for the U.S. fossil fuel industries, and especially the struggling coal sector.

Hillary Clinton, by contrast, wants to continue and extend Obama’s climate policies, including striving to reach the U.S.’s Paris agreement target of cutting our greenhouse gas emissions by 26 percent or more below 2005 levels by 2025. She also wants to, as she has put it many times, make the U.S. a “clean energy superpower” by stoking growth of the solar and wind industries.

That’s quite a contrast. But at the same time, and as many have noted, the mainstream presidential election discussion of the past two months, and especially the presidential debates, has tended to ignore all of this. (I was fortunate enough to participate in an exception to this trend Wednesday on the “Diane Rehm Show.”)

So let’s look more closely at how it is that Earth’s most momentous and depressing environmental problem has somehow stayed mostly out of what some would say is Earth’s most momentous and depressing election – and what the implications for climate and energy would be, depending on who wins on November 8.

Climate silence?

First let’s think back about two weeks. (I know it’s hard.) Environmentalists, and liberal pundits, were aghast. The third presidential debate had ended, concluding a presidential debate season in which the topic of climate change wasn’t asked about by any of the moderators, and only came up relatively briefly as a Hillary Clinton talking point.

The real subtext here: A lot of people on the left wanted to see Donald Trump try to defend his stance of climate change doubt, even as Clinton prosecuted the case that such a view is denying science, etcetera, etcetera. Bring popcorn, right?

But I would assert to you that even if it had happened, that would not have been a major moment in this election. Here’s why.

The truth is that in this race, Hillary Clinton has made much of the climate issue, brought it up repeatedly, campaigned with Al Gore in Florida and linked a changing climate to ferocity of Hurricane Matthew, and much more. That’s far more than President Obama did in 2012. Unlike Obama, apparently, Clinton saw it as a political winner for her, particularly with millennials and Bernie Sanders followers.

All in all, you could argue it’s a very substantial change for the issue of the climate in recent U.S. elections. It’s an elevation and a prioritization. It’s just that it has happened during a race that has been extremely scandal-focused, extremely negative, and obsessed in all ways with Donald Trump – and that has been a unique aspect of this election.

If Clinton had been running against Marco Rubio, or John Kasich, or Ted Cruz, it’s likely the subject would have come up even more. So as I wrote earlier, in this election, there’s just really “no oxygen left for a serious debate about carbon.”

Climate and energy under a President Clinton

So what might we have heard, if the debates had explored these topics more extensively?

The truth is that we actually kind of know: While energy and environment matters barely came up in the presidential debates, the University of Richmond School of Law recently hosted an energy and environment debate between Clinton and Trump campaign advisers, and it was pretty illuminating. And indeed, there’s a huge gap between the contenders, especially on the existence and seriousness of human-caused climate change, although there are also interesting areas of agreement, like on nuclear power. (For a more thorough rundown of this debate, read Brad Plumer here.)

If Clinton wins, let’s face it: We know it’s going to be more of Obama. This is certainly one case where she represents the status quo.

Under Clinton, we can assume that the Paris process goes full speed ahead, the Environmental Protection Agency’s Clean Power Plan advances (assuming it survives its current legal challenges), and much more. Clinton has also made extremely bold clean energy pledges, such as her promise (as her campaign website explains) to, within 10 years, “generate enough renewable energy to power every home in America, with half a billion solar panels installed by the end of Hillary’s first term.”

In this scenario, many fascinating questions arise. For instance, it’s far from clear that generating all of our home electricity from intermittent renewables (wind and solar) is going to be feasible, given the nature of power grids and the fact that you can’t always count on the sun shining and the wind blowing. We will have to start asking, for instance, how much wind and solar power can grids handle in the U.S., especially in states like California, and how much will they need to back that up with energy sources that can fire up quickly when renewables slump. Those sources could be either natural gas, or, in the future, enormous grid batteries.

Another major question will depend not only on whether Clinton is elected president, but also the composition of the Senate and the House, and therefore, what is politically feasible. But the truth is that a centrist policy consensus has been emerging in recent years on how to fix climate change, in the wake of the political failure of cap-and-trade early in the Obama years.

Let’s not forget that the EPA’s Clean Power Plan arose in a context in which it seemed impossible for Obama to actually get a piece of major climate legislation through Congress. But beyond EPA regulatory action, there seems to be general agreement, especially among economists, on the need to set a price on carbon dioxide emissions. This would likely take the form of what is known as a revenue-neutral carbon tax, in which emissions are taxed but that revenue to the government is offset with tax reductions elsewhere, or paid back to citizens in the form of dividends.

The question is whether Clinton would pursue such a policy, if she finds herself with a Congress at all favorable to it. And it’s important to note that this is closely tied to another key energy question: What happens to two key low carbon energy sources — nuclear power and coal plants that have been designed so that their emissions can be captured and stored underground (so-called “carbon capture and storage”) — which many analysts believe will be needed to supplement wind and solar. Both electricity sources have been struggling — and both would be more competitively priced with a tax on carbon.

The politics of taxing carbon could get pretty interesting, as we see in Washington state, which has a carbon tax on the ballot as an initiative and actually, we’re seeing that some environmentalists and denizens of the political left are uncomfortable with it. One key divisive issue is the revenue-neutrality: These groups would like to use emissions reductions policies to also promote clean energy investments, rather than return revenues to taxpayers.

“If it passes, it’s going to be important, it’s going to be path-breaking, it’s going to set an example that will get attention in other states and importantly in Washington, D.C.,” Dallas Burtraw, a senior fellow at Resources for the Future, told me recently of the Washington state carbon tax push. But if that push fails, it may suggest that even the coalition of interest groups behind climate action is too fractious for certain policy approaches. So we’ll have to very closely watch this initiative and how it fares.

Finally, if Clinton is elected, perhaps the biggest battle is going to be over natural gas and fossil fuel infrastructure, as she draws pressure from the left and the anti-fracking crowd, which believes that the transition away from fossil fuels has to be super fast and that even relying on lower-emitting natural gas is a luxury we can’t afford. “The climate movement has to elect Hillary Clinton — and then give her hell,” writes the movement leader and journalist Bill McKibben.

Because of this push, we can expect continuing debates over whether or not natural gas is a “bridge fuel,” and how much fugitive methane emissions undermine that role, and whether regulating those away will be enough. In general, the question of methane — how much we’re emitting from fossil fuels, as opposed to from other sectors, like agriculture, and how much that matters — will continue to be a major debate in coming years, in significant part because the issues here remain more uncertain than are those surrounding the principal greenhouse gas, carbon dioxide.

Thus, under Clinton, we should expect the U.S. executive branch to take every step that it can to try to reduce our greenhouse gas emissions and advance the global climate process — but we should also expect a series of hard questions to arise when it comes to the precise nature of the transition to less carbon-intensive energy in the U.S., and what that means for natural gas, nuclear energy, and just maybe, a cleaner way of burning coal.

It’s worth noting, incidentally, that this runs in an interesting parallel to what other countries that are committed in a major way to grappling with climate change through their energy systems, like Germany, are now facing.

Climate and energy questions in a Trump presidency

Trump is expected to try to withdraw from, or simply not participate in, the Paris process. One question is precisely how Trump would attempt to extricate the U.S., given that the agreement will be in force and its language states that a party cannot withdraw for three years, followed by a one-year waiting period. A lot of analysts have spun out scenarios for how this would occur.

In the video above, Trump energy adviser Kevin Cramer, a U.S. representative from North Dakota, argues that a Trump administration would submit the agreement for ratification to the Senate — something the Obama administration argues is not required for this type of agreement — and that it would likely fail there. Yet it isn’t clear what happens in this case, since the U.S. has already, in an international context, formally joined the accord.

Legal points aside, it’s pretty obvious that a Trump administration could simply fail to participate in the Paris process — just not engage — and there’s not much that the world could do about that, other than very loudly disapprove. At that point, a key question would be whether there is so much global perception of urgency that we would see other nations move forward anyway, even without the United States, with the hope of waiting out a Trump administration and banking at least some emissions cuts in the meantime.

The Paris Agreement entered into force on Friday, Nov. 4, 2016. The Post's Chris Mooney explains where we go from here. (Daron Taylor/The Washington Post)

Meanwhile, back at home, Trump has repeatedly pledged to try to help the domestic coal industry. And an enormous question is how he would actually go about doing that. Given that Trump has tended to misdiagnose that industry’s problems – pinning them rather exclusively on EPA regulations, rather than also crediting the surge in competition from natural gas, which has changed the economics for utility companies – it’s not clear that he could succeed.

Interestingly, Trump often talks about “clean coal.” And it’s true that the climate concerns about burning coal would lessen greatly if large percentages of the emissions were being captured and sequestered in some way, but the industry just isn’t ready to do that at a large scale at this point. Would Trump invest further in clean coal technology and even consider carbon pricing, to help carbon capture-and-storage compete?

Trump would also presumably try to thwart the EPA’s Clean Power Plan, if it survives the courts — though it’s not entirely clear how that scenario plays out either. Based on some analyses of what this would look like, it sounds like most courses of inaction, such as trying to create a new and different regulation that would be weaker, or failing to enforce the plan, would probably end up with environmental groups suing the EPA and throwing matters to the courts.

But let’s remember that the compliance period under the Clean Power Plan doesn’t start until 2022 anyway. And renewables and natural gas have so much momentum right now that U.S. emissions could actually continue to decline without it ever taking effect – perhaps even more so if electric vehicles continue the kind of growth we’ve been seeing.

After all, U.S. carbon dioxide emissions have been declining during the Obama years, without any Clean Power Plan in place, in part because of more burning of natural gas and also, increasingly, more renewables:

To see why renewables could advance even under Trump, consider the state of Texas, a state that regularly votes Republican in presidential elections, but also leads all of the United States in the amount of wind energy generating capacity that it has installed. And in fact it’s not even close: Texas has over 18 gigawatts (or billion watts) of wind capacity right now, with another 5 on the way. The second two states, Iowa and California, were around 5 to 6 gigawatts.

So it’s quite possible that Trump could come into office, reject climate change, reject the international climate process, and we could still actually see U.S. emissions tick down at least somewhat over the course of four years, thanks simply to the free market and technology.

Granted, it’s dubious this would be at a rate that would match Paris climate targets, or anything like what Clinton would achieve by actively trying to produce such an outcome. And given that the world is in urgent need to ramp up its pace of emissions cuts, those differences could have major implications for international climate cooperation (to say nothing of the physical climate system).

And there’s perhaps one more thing to point out. Today we’re seeing a pretty dramatic conflict over a piece of fossil fuel infrastructure: the Dakota Access Pipeline. In recent years a “keep it in the ground” movement has arisen that has increasingly targeted such projects. Under Trump, it seems likely that such demonstrations would increase, perhaps markedly, as a lack of climate action through policy would spur more attempts to push climate action through protests.

Most of all, we should expect climate change to be a far more salient political issue under a Trump presidency — a major source of sharp conflict — simply because of the obvious high-profile political and international conflagrations that would ensue if he keeps his campaign pledges.

Oh, and one more thing: We’ve had a run of very hot years lately, but we can also expect that the years of the next presidency will likely keep pace with the warmth of the 2010s so far — if not bringing still more records.

In that case, maybe by 2020, a debate moderator would indeed ask about climate change.

This article draws on remarks Chris Mooney gave on Oct. 31 at the 2016 annual meeting of the National Association of Science Writers.

Read more at Energy & Environment:

Global warming could be breaking up this 200 million year old relationship

We’re adding record amounts of wind and solar — and we’re still not moving fast enough

It could be the nation’s first carbon tax. And environmentalists are fighting over it

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