Donald J. Trump will head to the heart of America’s and gas boom on Thursday to unveil details of his policies on energy and the environment.

Speaking at an oil industry conference in Bismarck, N.D., Mr. Trump is expected to embrace standard Republican calls for more fossil fuel drilling and fewer environmental regulations, while possibly elaborating on his positions on .

Mr. Trump has backed some energy policies, such as requiring more ethanol production, that are widely criticized by energy experts. He has made contradictory remarks on alternative energy sources, such as wind and solar. And he has made pledges — for example, to restore lost jobs in coal mining — that essentially defy free-market forces.

“Many of his proposals thus far don’t seem to appreciate the complex forces that drive the energy system,” said Richard G. Newell, director of the .

Mr. Trump’s decision to set his speech in North Dakota was politically strategic. He is fewer than 30 delegates shy of clinching the Republican presidential nomination, and North Dakota’s 28 unpledged delegates could get him to the magic number.

A central question confronting the next president will be climate change. Mr. Trump has forcefully denied the established science that it is caused by humans, saying in a radio interview last year, “I’m not a believer in man-made global warming.”

Mr. Trump has said he would undo President Obama’s climate change policies, particularly a set of Environmental Protection Agency regulations to curb planet-warming emissions . Of the E.P.A. itself, he “to get rid of it in almost every form.”

He has said that as president, he would renegotiate the , a global agreement committing nearly every nation to lowering greenhouse gas pollution. And, while demand for American coal has declined, he declared while campaigning in West Virginia, “We’re going to get those miners back to work.”

Interactive Feature | Short Answers to Hard Questions About Climate Change The issue can be overwhelming. The science is complicated. We get it. This is your cheat sheet.

But, as , Mr. Trump’s organization cited global warming and its consequences in a permit it filed to build a wall to protect against erosion at his seaside golf resort in County Clare, Ireland. And in an environmental impact statement from a smaller project in 2003, his organization also cited “sea level rise” and “global warming” as reasons to build a small cobble and rock wall at three sections of a beach.

Whether Mr. Trump could fulfill his energy pledges is an open question. The centerpiece of Mr. Obama’s climate change rules in federal courts. If, as is widely expected, the case goes to the Supreme Court, the justices, rather than the president, will determine its fate. But if elected president, Mr. Trump could nominate a new Supreme Court justice to help strike down the rule.

Dismantling the E.P.A. would be trickier. The president does not have unilateral authority to eliminate an agency, and even proposals to limit its authority would have to go through Congress. And simply cutting its authority would not end its responsibility to carry out existing environmental laws.

“Even if Congress did vote to eliminate the E.P.A., they would cause huge problems unless they also went back and redid some of these laws,” said Jeffrey R. Holmstead, who was an E.P.A. official under President George W. Bush. “You would cause quite a train wreck if you were to simply do away with the E.P.A.”

While Mr. Trump says he would renegotiate the Paris agreement, its fate may be determined before the next president takes office. Once the accord is ratified by 55 countries representing 55 percent of global emissions, it will enter into legal force, and any country wishing to withdraw would have to wait four years to do so. However, if the deal has not been ratified by January 2017, a new American president could withdraw immediately. For that reason, many countries are racing to ratify the deal this year.

It is unclear how Mr. Trump could restore lost jobs in the coal industry. As domestic coal demand has declined, companies have laid off thousands of miners. But economists say that shift is driven by market forces: The boom led power companies to buy cheaper gas rather than coal.

“Most analysts would say that coal is hurting because natural gas prices have collapsed,” said Robert McNally, the president of the Rapidan Group, an energy consulting firm, and a senior energy official in the Bush administration. “ would have to find a way to raise natural gas prices.”

On renewable energy, Mr. Trump has been inconsistent.

In 2005, he wrote on his blog, “I wish that the United States would just get on the ball with alternative energy,” and suggested that funding for the space program “should be redirected into research that would develop other ways of fueling our nation.”

Graphic | Where Trump Breaks With the Republican Party Donald J. Trump is set to be the Republican standard-bearer, but when it comes to some of his policies, he is out of sync with many Republican leaders in Congress.

But in his 2015 book, “Crippled America,” Mr. Trump called the government’s push to develop renewable energy “another big mistake.”

Yet while campaigning in Iowa, where makes up more than 25 percent of electricity, he said he was “O.K. with” subsidies for wind power.

Mr. Trump also sought to court Iowa voters by supporting corn-based ethanol. Current law requires annual production of 15 billion gallons of corn-based ethanol. This has benefited Iowa’s farmers but, experts say, harmed the rest of the country, raising food and fuel costs while yielding little environmental gain. A bipartisan coalition of federal lawmakers has pushed to repeal the mandate. But while campaigning in Iowa, Mr. Trump said he was “100 percent” behind the mandate and would even raise it.

“That doesn’t make a lot of sense,” said Mr. Newell of Duke University. “It’s already so ambitious that it’s been difficult for industry to meet.”

Over all, experts remain skeptical of Mr. Trump’s command of the complexities of the global energy economy.

“I have no idea whether he’ll show the same mastery of international oil markets that he does of women’s issues,” said Tom Kloza, an analyst at the Oil Price Information Service.

This month, Mr. Trump met with Robert E. Murray, the chief executive of Murray Energy, a major coal producer, seeking policy advice. He appeared befuddled by a question about liquid natural gas, according to , and asked, “What’s L.N.G.?”

Mr. Trump has tripped over other policy terms as well.

In a recent Fox News interview, he said, “Department of Environmental, I mean, the D.E.P. is killing us environmentally,” evidently referring to the E.P.A.

On Wednesday, Mr. Trump’s campaign was still finishing work on his remarks and deciding whether he would deliver them from a teleprompter, as he has with other major policy speeches. In recent weeks, he has delivered several policy addresses in Washington, including before the American Israel Public Affairs Committee and another .