Shell squared off against seven environmental groups in a Dutch appeals court Tuesday, with climate activists accusing the multinational oil giant of failing to implement a landmark 2021 judgment.

Judges at The Hague District Court ruled three years ago that Shell must reduce its carbon emissions by 45 percent by 2030, as it was contributing to the "dire" effects of climate change.

That ruling was seen as a historic victory for climate change campaigners as it was the first time a company had been made to align its policy with the 2015 Paris Climate Change Accords.

Shell, which called litigation "ineffective" to address climate change, is appealing the 2021 ruling, while environmental groups accuse the oil giant of failing to take action.

"Justice delayed is justice denied," said Donald Pols, who heads Milieudefensie, the Dutch arm of Friends of the Earth, who originally brought the case.

"I hope this case will change the way that Shell does business... as it is currently one of the largest polluters in the world," he added.

"We are very confident. We have been working for more than two years towards this moment," Pols told AFP outside the Hague courthouse, where four days of hearings are scheduled.

A new study revealed "that Shell will continue to invest billions of dollars in (new) oil and gas projects for decades to come," Milieudefensie added in a statement ahead of the case.

The study, by Milieudefensie and fossil fuel research group Oil Change International, added that London-based Shell "also made the final decision to approve construction of 20 major oil and gas projects, including six in 2023 alone."

"The scientific basis on which we've founded our claims against Shell has only solidified," Milieudefensie's lawyer Roger Cox said ahead of the hearings.

"In court, it's facts that matter. That's why I am confident that we can once again convince the judges that Shell needs to act in line with international climate agreements," he said in a statement.

  'Simply not effective' 

 Shell hit back ahead of the hearing, denying it was ignoring the 2021 court ruling.

"A civilian judge simply is not equipped to make rulings in a civil case which has national and political implications," Shell's lawyer Daan Lunsingh Scheurleer told AFP.

"We too find that urgent action is needed to stop climate change," Shell Netherlands chief executive Frans Everts added.

"But this court case is not the way to achieve that aim," Everts told AFP at the start of the hearing.

"One ruling against an individual company is simply not effective if the issue simply continues to exist," he said.

Shell said it believed the 2021 verdict "was ineffective and even counterproductive in tackling climate change," but denied it was ignoring it.

Shell said it was investing some "10 to 15 billion dollars between 2023-25 in low-carbon energy solutions," representing 23 percent of its total capital expenditure.

"If this judgment is upheld, it will have far-reaching consequences for Dutch business, employment, and the Dutch investment climate," the company warned.

The 2015 Paris accords committed all nations to cut carbon emissions to limit warming to two degrees Celsius (3.6 Fahrenheit) above pre-industrial levels and encouraged them to go down to 1.5 degrees.

A decision by the judges is expected within the next three months.