Greenpeace Italy and the Italian advocacy group ReCommon aim to build on a similar case targeting the Anglo-Dutch oil major Royal Dutch Shell in the Netherlands to force Eni to slash its carbon emissions by 45 percent by 2030.

“The urgency of taking action against the climate crisis has prompted us to bring the first climate lawsuit in Italy against the country’s largest energy company,” said Matteo Ceruti, a lawyer for the plaintiffs.

The allegations rest in part on a study Eni commissioned between 1969 and 1970 from its Isvet research centre, which has been shared with The Guardian by the nonprofit climate news service DeSmog. The report made clear that left unchecked, rising fossil fuel use could lead to a climate crisis within just a few decades.

“[C]arbon dioxide in the atmosphere, according to a recent report by the UN secretary, given the increased use of [fossil fuels], has increased over the last century by an average of 10 percent worldwide; around the year 2000 this increase could reach 25 percent, with ‘catastrophic’ consequences on climate,” the report said.

Greenpeace Italy and ReCommon have also unearthed a 1978 report produced by Eni’s Tecneco company, which included a projection of how much atmospheric CO2 levels would rise by the turn of the century.

“It is assumed that with the increasing consumption of fossil fuels, which began with the Industrial Revolution, the CO2 concentration will reach 375-400 [parts per million or ppm] in the year 2000,” stated the report. “This increase is considered by some scientists as a possible long-term problem, especially since it could change the thermal balance of the atmosphere leading to climate changes with serious consequences for the biosphere.”

This prediction would prove to be broadly accurate. Between 1970 and 2000, Earth’s atmospheric CO2 concentration rose from 325ppm to 371ppm. It is now about 420ppm.

Further research by DeSmog has shown that Eni’s company magazine Ecos made repeated references to climate change during the late 1980s and 1990s — while running advertising campaigns promoting planet-warming natural gas as a “clean” fuel.

Eni did not respond to a request for comment on the documents.

The lawsuit will also name two government entities — the ministry of economy and finance, and the development bank Cassa Depositi e Prestiti — for the “influence they exercise on Eni,” the writ of summons states. Between them, the ministry and the bank hold the Italian government’s one-third ownership stake in Eni.

Greenpeace Italy and ReCommon announced the lawsuit at a news conference in Rome on Tuesday, held on the eve of Eni’s annual general meeting. The groups say they intend to file the suit in the civil court of Rome by May 19 and will request that hearings begin in November.

Experts in climate litigation say the documents associated with the Eni case add to a growing body of evidence that oil companies had a clear understanding of the risks posed by burning their products more than half a century ago, but still chose to downplay the dangers and ramp up production of oil and gas.

“These findings reinforce and add to the pattern found in previous research: Oil majors understood the catastrophic effects their products would have on the world, yet failed to warn the public, concealed their knowledge, denied the problem, and obstructed efforts to solve it,” said Ben Franta, a senior research fellow at the Oxford Sustainable Law Programme. “Like other fossil fuel companies, Eni might ultimately be held accountable in court for this pattern of deception and harm.”

With a market capitalization of nearly $49bn (£39bn), Eni typically appears among the world’s top dozen richest oil companies. In 2022, Eni reported a profit of $14.12bn, up $9.9bn from 2021. The company operates in more than 60 countries and at all levels of the oil and gas sector — from exploration and drilling to petrochemical manufacturing.

Eni ranked 24th among global oil and gas majors for cumulative carbon dioxide and methane emissions from 1950 to 2018, according to an analysis by the Climate Accountability Institute.

Two landmark climate cases in the Netherlands have raised the Italian campaigners’ hopes that they can use litigation to force companies and governments to rapidly cut climate-heating carbon emissions.

In 2019, the Dutch supreme court upheld a lower court ruling siding with the Urgenda Foundation, an environmental group, and ordered the Dutch government to adopt more ambitious targets for reducing emissions. Two years later, The Hague district court ruled in favour of Friends of the Earth Netherlands, Greenpeace Netherlands and other groups that sued Shell to slash its emissions 45 percent by 2030. Shell has appealed against the ruling.

The Italian case also bears a resemblance to a swelling number of consumer fraud lawsuits against big oil by states, cities and municipalities in the US. The supreme court in April declined appeals by Exxon Mobil, Chevron and Suncor Energy to move five of these cases from state to federal courts.

In April 2020, the Italian competition authority said it had fined Eni about $5.5m for misleading consumers with “green” claims in a diesel fuel ad campaign. Last year, environmental groups filed a complaint with the Organization for Economic Cooperation and Development, an intergovernmental body, alleging that Eni’s plans to increase oil production ran contrary to its goal of reaching net zero emissions by 2050. That case is still pending.

Eni said it would prove the new lawsuit was “groundless,” and, if necessary, demonstrate in court that it had taken the correct approach to decarbonisation. “The strategy combines and balances the essential objectives of sustainability, energy security and competitiveness of Italy,” Eni said in a statement.

The company added that it reserved the right to take legal action to protect its reputation in response to “repeated defamatory actions” undertaken by ReCommon.