COPENHAGEN, Denmark << Denmark pushed the button Wednesday on an ambitious project that aims to bury vast amounts of planet-heating carbon dioxide gas beneath the North Sea floor, in the hope that it can help the Nordic nation and others meet climate targets.

An international consortium including chemicals giant INEOS and gas and oil producer Wintershall Dea said Project Greensand in Denmark’s North Sea will be the world’s first cross-border carbon storage project.

Denmark’s Crown Prince Frederik gave the symbolic order to begin pumping CO2 into the depleted reservoir of the Nini West oil field, 50 years after his father Prince Henrik celebrated the start of oil and gas exploration off the Danish coast.

“It gives me great pleasure today to be able to reverse the traffic in the pipes and send CO2 back into the Danish underground to the benefit of the climate for Denmark, for Europe, but also for the planet,” said Frederik.

Initially the gas will be shipped in liquid form from an INEOS plant in Belgium, but the plan is to bring in CO2 from Denmark and other European countries later on. After a pilot stage it will see 1.5 million metric tons of the greenhouse gas buried in a sandstone reservoir 1.8 kilometers (1.1 miles) below the seabed each year, rising to 8 million tons per year by 2030.

In a recent report, the United Nations Intergovernmental Panel on Climate Change said carbon capture and storage technology has to be part of the range of solutions to reduce emissions and cap global warming at 1.5 degrees Celsius (2.7 Fahrenheit) compared with pre-industrial times.

“To keep global temperatures below 1.5 degrees we need to remove carbon on top of our efforts to reduce emissions,” European Commission President Ursula von der Leyen said in a video address at the Greensand launch event.

She noted that the 27-nation European Union needs to capture and store about 300 million tons of CO2 annually by 2050 if it wants to be climate neutral, meaning all the greenhouse gas emissions still produced then will have to be removed again somehow.

“This is a staggering amount,” said von der Leyen.

Experts warn that carbon capture and storage is still an unproven technology and relying on it could undermine efforts to decarbonize the energy sector.

Bruce Robertson, an analyst with the Institute for Energy Economics and Financial Analysis, said the technology for sequestering carbon was first developed in the 1970s to help boost oil production. By pumping gas underground, fossil fuel companies could force more oil and gas out of existing wells.

While several recent projects have focused on the climate benefits of storing carbon underground, these have been largely unsuccessful, he said.

Robertson cited the Gorgon project in Australia, driven by industry majors such as Chevron, Shell and Exxon, who attract the best petroleum engineers in the world. “And they can’t get this project to work,” he said. “It’s underperforming pretty radically.”

Energy company Equinor has successfully stored carbon in two reservoirs off the coast of Norway but had to stop a project in Algeria because carbon dioxide “started going all over the shop,” said Robertson.

Each project requires a costly bespoke solution because the underground conditions can be radically different and there is no certainty the CO2 won’t be released again, for example if there is an earthquake, he said.

“You are setting up a series of carbon bombs underground that may go off at some undetermined point in the future,” he told The Associated Press in a video interview from Australia.

Robertson noted that a large amount of energy is also needed to capture and bury the CO2, most of which comes from industrial processes or fossil fuel extraction. And it does nothing to remove the carbon dioxide released from burning fuel — such as in cars or home heaters — which makes up the majority of emissions.

“Carbon capture and storage for the oil and gas industry is only addressing a very small amount of the problem and not the elephant in the room,” he said.

Maeve O’Connor, an analyst at the nonprofit energy research group Carbon Tracker, said it was important the emissions captured by the project aren’t used to justify increased production, but actually result in a net reduction of emissions.

“We often see oil and gas companies issue lofty announcements about breakthrough projects, but the reality is that if the company does not concurrently rein in production, their greenhouse gas emissions will continue to grow and the world’s 1.5 C goal will get harder and harder to reach,” she said.

Still, the International Energy Agency predicts that the most ambitious transition to net zero emissions would require 1.5 billion tons of CO2 to be stored or otherwise used globally by 2030, rising to 6.2 billion tons in 2050. Governments, including in the United States and Europe, are already setting aside considerable subsidies for carbon capture and storage, or CCS.

Denmark’s climate and energy minister, Lars Aagaard, made clear that his country wants a piece of that pie.

“There is, pardon my French, no chance in hell that we will meet the global climate targets without CO2 storage,” he said. “It’s a tool that we need.”