After moving last month against former President Barack Obama’s efforts to limit fossil fuel exploration and combat climate change, President Donald Trump will complete his effort to overturn environmental policy this week, signing two executive orders to expand offshore drilling and roll-back conservation on public lands.

On Wednesday, Trump will sign an executive order directing his interior secretary, Ryan Zinke, to review national monuments designated by previous presidents under the Antiquities Act of 1906, aiming to roll back the borders of protected lands and open them to drilling, mining and logging.

The President is then expected to follow up on Friday with another executive order aimed at opening up protected waters in the Atlantic and Arctic oceans to offshore drilling. The order would direct Zinke to revisit an Obama administration plan that would have put those waters off limits to drilling through 2022. Friday’s order is also expected to call for the lifting of a permanent ban on drilling in an area including many of those same waters — a measure Obama issued in December 2016 in a last-ditch effort to protect his environmental legacy from his drilling-enthusiast successor.

The moves — just before Trump’s 100th day in office — would begin to fulfil a central campaign promise to unleash a wave of new oil and gas drilling and create thousands of jobs in energy.

The reality is more complicated, said experts in the law, policy and economics of energy. The orders are not likely to lead either to significant new energy development or to job creation in the near future. With oil prices around $50 a barrel and production already glutting world markets, few oil companies are making plans to expand into costlier, riskier offshore drilling.

And the process of undoing Obama-era regulations will take more than a flick of Trump’s pen. The legal challenges that the orders will face could take years to resolve. And without additional action from Congress, they could be reversed by Trump’s successor.

“You don’t create jobs by signing a piece of paper if those jobs rely on a combination of economics and technology that the president doesn’t control,” said Kevin Book, a managing director at ClearView Energy Partners, a Washington analysis firm.

That does not mean that both sides of the energy production debate are shrugging off the president’s moves. Oil and gas companies and Trump’s political supporters are cheering, even as they concede that this week’s signing ceremonies will not produce new oil rigs in the next few years.

Environmental groups warn that just opening the door to future drilling in pristine federal lands and waters could lead to more disasters like the 2010 oil spill in the Gulf of Mexico, which sent millions of barrels of oil to the shorelines of coastal states, killing wildlife and destroying fragile ecosystems.

“These might not necessarily result in near-term oil and gas production, but it could expand our opportunities in the future,” said Erik Milito, the director of upstream issues for the American Petroleum Institute, which lobbies for oil companies.

Jacqueline Savitz, a vice president of Oceana, which campaigns aggressively against the drilling, declared, “Offshore drilling in the Atlantic and the Arctic is still dirty and dangerous.”

“The Arctic is the most dangerous place you can be drilling offshore: It’s dark, icy and far away from disaster response teams,” she said.

Environmentalists were no more receptive to the review of the Antiquities Act.

“It is clear that this ‘review’ is a thinly veiled attempt to appease special interests and sell off our national parks, public lands, oceans and cultural heritage to the highest bidder,” said Christy Goldfuss, vice president of energy and environment policy at the liberal Center for American Progress, and a former environmental policy official in the Obama White House.

She added: “Our monuments — from the Grand Canyon to Zion to Papahanaumokuakea and Stonewall National Monument — are majestic, historic and uniquely American. No president has ever attempted to revoke a national monument, and to mark his 100th day, President Trump is entering a legal, political and moral minefield.”

In the century since Theodore Roosevelt signed the Antiquities Act into law, presidents have used the law to put hundreds of millions of acres of land and waters off limits to development, and no president has undone a predecessor’s designations.

But Trump’s supporters say that in recent years presidents have overused and abused that authority. Obama designated about 553 million acres as national monuments, more than any other president.

Zinke said the review of those monuments would include only designations made since 1996, stretching over 100,000 acres.

“I can tell you as a kid who grew up in Montana, the West, where much of those monument designations took place, this review is long overdue,” Zinke, a former Montana congressman, said in a conference call with reporters.

Still, Zinke, who is a lifelong hunter and fisherman, said his love of the land would play into his review: “I’m a Teddy Roosevelt guy. You can’t love public lands more than I do.”

Legal experts say it will still be a heavy lift for the Trump administration to change the designations. “The Antiquities Act language does not include any authority for presidents to rescind or modify a national monument created by predecessors,” said Mark Squillace, an expert on natural resources law at the University of Colorado Law School. “That authority is limited to Congress.”

Trump will also run into legal hurdles in some of his efforts to roll back Obama’s offshore drilling protection. Just before leaving office, Obama invoked an obscure provision of a 1953 law, the Outer Continental Shelf Lands Act, which he said gave him authority to act unilaterally to create a permanent drilling ban on portions of the ocean floor from Virginia to Maine, and along much of the Alaska coast.

“We’re in uncharted waters,” said Jason B. Hutt, a lawyer with the firm Bracewell who represents fossil fuel companies. “There is precedent for a president to narrow or modify drilling restrictions, but not to undo a ban, because there’s never been a ban.’

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Trump is within his rights to overturn Obama’s ban on drilling in portions of the Arctic and southeastern Atlantic Coast through 2022. But even his allies noted that such a move would be unlikely to lead to rigs in the water for several years, and that it could easily be reversed by Trump’s successor.

“It’s certainly not going to happen tomorrow. No one is saying, all of a sudden, there’s going to be drilling everywhere,” said Thomas J. Pyle, an adviser to the Trump transition and the president of the Institute for Energy Research, an organisation partly funded by the billionaire brothers Charles G. and David H. Koch. “It will involve a lot of effort by agencies. It will involve lawsuits. And hopefully it will involve Congress, so they can cement these” changes in place.