In August, President Obama ensured that climate change will be one of the major issues at stake in the 2016 election. Whether candidates choose to talk about it or not, whoever gets elected president next year will have enormous influence over US climate and energy policy.

The reason is simple. Back in 2007, the Supreme Court gave the Environmental Protection Agency unprecedented authority to regulate US greenhouse gas emissions under the Clean Air Act. In the years since, Obama has used that power to enact sweeping new climate rules. That includes stricter fuel efficiency standards for cars and trucks. It also includes the Clean Power Plan, an ambitious EPA rule to cut CO2 emissions from the nation's power plants, which was finalized in August.

Whoever gets elected in 2016 will have enormous influence over US climate policy

These regulations were all enacted without Congress. And their ultimate fate rests with the next president. If a Republican like Donald Trump gets elected in 2016 and wants to weaken the Clean Power Plan or relax those fuel economy rules, he'll have a lot of leeway to do so (though total repeal could prove difficult, as we'll see). By contrast, if Hillary Clinton wants to come in and massively expand what the EPA's done, she'll have plenty of options — such as extending carbon regulations to refineries, chemical plants, or aircraft.

"Any future administration will have a lot of room to be either more ambitious or less ambitious," explains Michael Wara, an expert on energy and environmental law at Stanford. And unlike with tweaks to Obamacare or federal tax policy or a host of other issues, this won't require Congress's approval.

Which path the next president chooses could have ripple effects around the world. As part of ongoing international climate talks, Obama has pledged that US greenhouse gas emissions will be at least 26 percent lower in 2025 than they were in 2005. We're not quite there yet — and the policies Obama has put in place thus far will only get part of the way:

So it's up to the next president. He or she could amplify Obama's policies and aim to hit that 2025 target — hoping, like Obama has, that this will inspire other countries to respond in kind with their own actions. (There's at least some reason for optimism: This past year, countries like China and Brazil have pledged to increase their climate efforts.) Or the next president could scale back Obama's climate policies significantly, at the risk of letting global talks stall out.

So far, presidential candidates have stayed fairly hushed on this issue. In an ideal world, they'd be asked about it at every turn. Here's a look at the options available to whomever takes the White House in 2016.

How a Republican president could dismantle Obama's climate policies

Many of the current Republican presidents have expressed hostility to Obama's EPA regulations, including the Clean Power Plan. Scott Walker, for instance, has called it a "buzzsaw to the nation’s economy."

So let's say a conservative hostile to Obama's climate policies becomes president in 2016. What options does he actually have?

1) Sign a bill that handcuffs the EPA. If next year's election brings us a Republican president with majorities in the House and Senate, he or she could always just pass a bill amending the Clean Air Act and curtailing the EPA's authority over greenhouse gas emissions. Boom, done. This could range from blocking or modifying the Clean Power Plan to barring the EPA from ever regulating CO2 emissions in any sector.

2) Replace the Clean Power Plan with a new regulation. Alternatively, let's imagine our Republican president doesn't have majorities in Congress. Now things get trickier. A President Scott Walker can't just refuse to regulate greenhouse gas emissions entirely. After all, the Supreme Court has ordered the EPA to do so as long as there's evidence they cause harm (and that evidence is quite solid.)

So instead, a new president might have to take subtler steps to weaken Obama's climate policies. Take the Clean Power Plan, which will force states to start cutting power plant emissions by 2022. One option is for a Republican president to initiate a new rulemaking process through the EPA to either undo Obama's plan or replace it with another, less ambitious rule. The hitch? This would take at least 12 to 15 months — it involves a notice, a proposed rule, soliciting public comment, and so on. And the process would likely get bogged down by lawsuits from environmental groups (who are very, very skilled at this sort of litigation). Doable, but surprisingly difficult.

3) Implement the Clean Power Plan, but very loosely. Or the next president could opt for a quieter approach — allow Obama's Clean Power Plan to proceed, but implement it weakly. In theory, there's room to do this. Under the rule, states have to submit plans for how they'll cut their power plant emissions by 2016, but they can request an extension until 2018. The EPA will then have to review the plans to make sure they're robust. An administration that wasn't very concerned about global warming might be able to get away with approving less aggressive plans from recalcitrant states like Texas or West Virginia.

"There’s a lot of latitude in the review process," says Stanford's Michael Wara. "The history of the Clean Air Act shows this. If you have a president who doesn’t like climate policy, they could basically signal to the states that they’re going to give a lot of compliance flexibility and allow states to make assumptions in their plan that reduce their costs." This would likely involve seemingly arcane tweaks to models and baselines that would be harder for green groups to challenge in court.

Meanwhile, some states may outright refuse to submit any plans for reducing emissions. (Sen. Mitch McConnell, R-KY, is already urging states to do exactly this.) If that happens, the EPA has the authority to impose its own federal plan on the states — but that implementation will be left to the next president. So, again, a Scott Walker administration could implement a federal rule that went easy on recalcitrant red states.

4) Fail to defend Obama's climate regulations in court. Industry groups are planning to challenge aspects of the Clean Power Plan in court, and those cases will take years to resolve. Adele Morris, the policy director for the Climate and Energy Economics Project at the Brookings Institution, pointed out that an administration hostile to Obama's EPA rule could always just defend it weakly in court. Plus, if any parts of the rule do get struck down, the next administration will get to decide how to redo it.

5) Loosen up Obama's fuel economy standards. A Republican administration could fiddle with other Obama climate rules, as well. For instance, the EPA has been ratcheting up fuel-economy standards for new cars and light trucks, which are now scheduled to rise from their current 35 miles per gallon to 54.5 miles per gallon by 2025.

But those numbers aren't set in stone. These CAFE (corporate average fuel economy) rules come up for a midterm review in 2017. At that point, automakers could lobby to allow the standards to rise more slowly — particularly if sales of fuel-efficient vehicles continue to be sluggish due to low oil prices. And an administration skeptical of these rules would have some room to relax them.

The one twist, however, is that due to a longstanding quirk of the Clean Air Act, California can threaten to create its own stricter vehicle standards if it's not happy with what the federal government is doing (and other states can join in). Automakers loathe the idea of multiple sets of vehicle standards around the country, so they may not want to weaken the federal rules too much and risk having California go rogue.

6) Decline to pass any new regulations. Technically, the EPA is supposed to keep regulating carbon dioxide until it covers all major sectors of the economy. That's the ultimate logic of that 2007 Supreme Court decision. But a Republican administration that didn't want to do this could probably drag their heels on this. Yes, they'd get sued by green groups, but they'd probably be successful in delaying new regulations. George W. Bush's administration managed to slow-walk a variety of rules, such as regulations on mercury pollution, for years.

If a new Republican administration put a halt to EPA regulations — and Congress also refused to act — then it'd probably be quite difficult for the United States to hit its goal of cutting emissions at least 26 percent below 2005 levels by 2025. The big question is whether that'd spur other countries like China to abandon some of their own climate efforts and unravel global climate accords.

How Hillary Clinton could expand Obama's climate policies

On the other side, Hillary Clinton has said the EPA's climate rules should be "protected at all cost." Which means that if elected, she'd veto any attempts by a Republican Congress to repeal the Clean Power Plan and so on. That's clear enough.

The big question is whether she (or Martin O'Malley or Bernie Sanders or whoever) would expand Obama's policies — and go beyond what he's done.

After all, according to a recent analysis by the World Resources Institute, even all of Obama's climate regulations to date are unlikely to be sufficient to get US greenhouse gas emissions 26 percent below 2005 levels by 2025. More will still be needed. Congress could provide that "more," in theory. But if they don't, Clinton would also have a lot of power, using the EPA's authority, to do more all by herself. A partial list includes:

1) Strengthen energy efficiency standards for homes and buildings. The Department of Energy has the ability to scale up or tighten various energy efficiency standards for household appliances, residential boilers, commercial ventilation equipment, and so forth. This would help reduce energy demand and CO2 emissions.

2) Expand programs to reduce HFCs. The Obama administration has already begun cracking down on HFCs, a potent greenhouse gas often used in refrigeration and air conditioning. In theory, the next president could direct the EPA to accelerate the phase-out of the worst of these gases and help bolster recycling programs and pursue alternatives.

3) Start regulating industrial CO2 sources. Similarly, the next president could set the EPA loose regulating other sources of CO2 emissions. Under Obama, the EPA has only regulated CO2 from vehicles and power plants. But the agency technically has the authority to regulate refineries, cement plants, petrochemical plants, and so on. The WRI report suggests that the EPA under the next president could use this power to improve end-use efficiency and fuel switching in the industrial sector and bring down US emissions even further.

4) Crack down on methane leaks from oil and gas infrastructure. Under Obama, the EPA has already begun setting standards for methane leaks from new oil and gas wells. The next president could expand this authority to existing oil and gas wells — the source of 90 percent of leaks — as well as other natural gas infrastructure.

5) Expand fuel economy standards for cars and light trucks. As noted above, federal fuel economy standards for new cars and light trucks are currently set to keep rising each year until they reach 54.5 miles per gallon in 2025. The WRI report points out that the next president could tighten these standards further during the 2017 midterm review, or even extend them further — say, to 63 mpg by 2030. (Though, again, if low oil prices are blunting sales of fuel-efficient vehicles, this could be tough.)

6) Set carbon dioxide rules for aircraft. Countries around the world are planning to come to some sort of agreement on reducing emissions from flying in the next few years. The WRI report notes that the next administration could work with the EPA to set a rule to improve the fuel efficiency of new aircraft in the range of 2 to 3 percent annually.

7) Reduce methane from landfills and agriculture. The EPA has already proposed regulations on methane emissions from new landfills. It could go further to restrict emissions from existing landfills and coal mines, as well as look into ways to reduce emissions from agriculture (yes, that means tackling cow burps).

With all these actions and more, the WRI report notes, the United States could get its greenhouse gas emissions on a steady downward trajectory. That, by itself, wouldn't be enough to solve global warming. After all, other countries like China and India would have to continue taking stronger actions themselves. But it's a start.

Of course, it's also worth noting that a flurry of executive-branch rules and regulations isn't really a long-term climate plan. In order to help stave off drastic global warming, the United States will probably need to push down emissions 80 percent or more by midcentury. And that would require truly staggering changes. It won't be enough for coal and gas plants to get slightly more efficient under EPA rules. We'd have to replace virtually our entire energy system with a new, cleaner one.

That's the sort of thing that likely requires congressional action. Only Congress can fund R&D for new technologies or offer subsidies for clean energy. Only Congress can bring about dramatic changes to our grid infrastructure. Only Congress can enact an economy-wide carbon tax. Barring some creative flexibility on regulations, these are things the next president just can't accomplish without cooperation from the House and Senate. At best, he or she will only be able to get part of the way there.

In any case, all candidates should be asked about this. For instance, Jeb Bush has said he's "concerned" about climate change and that "we need to work with the rest of the world to negotiate a way to reduce carbon emissions." But what does this mean in practice? Would he stick with Obama's Clean Power Plan? Modify fuel economy rules? Maintain the 26 percent by 2025 target? Let's hear it.