Climate science is supporting lawsuits that could help save the world.

Governments have failed to slow climate change quickly enough, so activists are using courts to compel countries and companies to act — increasingly with help from forefront science.

Friederike Otto hadn’t really thought much about the legal world when she answered the phone one day in 2018. On the other end of the line was Petra Minnerop, a scholar of international law at the University of Durham, UK, who was exploring how the legal system might help to save the planet.

Minnerop had developed an interest in climate litigation — efforts to hold governments and companies legally responsible for contributing to global warming. Following the success of several climate lawsuits, she was seeking to get involved and thought Otto’s research might help. Otto, a climate modeller at the University of Oxford, UK, is one of the world’s leaders in attribution science — a field that has developed tools to assess how much human activities drive extreme weather events, including the heatwaves, fires and floods that have ravaged parts of the globe this year. In their telephone call, the pair realized that they had similar aims and they set about thinking how science and environmental law might trigger more action to limit climate change.

Minnerop and Otto are in the vanguard of scientists and legal scholars who are assisting in lawsuits to force governments and companies to take action against climate change. Over the past few decades, environmental groups and citizens around the world have filed more than 1,800 climate suits. Science has been central to supporting the arguments in these cases, but the vast majority have relied on the most basic conclusions of climate research. Now, Otto, Minnerop and others are seeking to bring in the latest science to improve lawsuits’ chances of driving substantial reductions in greenhouse-gas pollution.

“There’s a really big gap in many cases between what can be said scientifically and what is brought to courts,” says Otto.

Court order

The number of climate suits has surged in recent years, thanks in part to a growing youth climate movement that has injected fresh energy into activism aimed at protecting the planet. Since 2015, plaintiffs, including children, have filed more than 1,000 climate cases, according to an analysis¹ published in July by researchers at the Grantham Research Institute on Climate Change and the Environment in London (see ‘Climate cases on the rise’). In 37 cases, lawsuits allege that governments have not lived up to their promises to lower the risks of climate change or to set goals that are ambitious enough. These cases, which target systemic problems, have generated the most attention, and could have some of the most far-reaching consequences if they are successful. Other cases focus on specific projects or practices, such as coal mining in Australia or deforestation in Brazil.

Success at court was limited at first. But a string of wins in the past two years is raising hopes that the legal scales are tilting in favour of stronger climate action. In May, the District Court of The Hague ruled that the energy company Royal Dutch Shell must reduce its carbon emissions by 45% compared with 2019 levels over the next 9 years, arguing that the high level of current emissions by the group might contribute to imminent environmental harm to Dutch citizens.

A month earlier, the Federal Constitutional Court in Germany ordered the government to lay out a clearer strategy towards achieving its climate targets for the period after 2030. The country is the world’s seventh-largest greenhouse-gas emitter. A similar court ruling last year compels the Irish government to flesh out its climate mitigation plan and explain how it intends to meet the goal of cutting emissions by 80% by 2050, relative to 1990 levels.

These two cases follow a precedent set by a landmark decision in 2015 in the Netherlands — a few months before nations agreed in Paris to limit global warming to well below 2 °C relative to pre-industrial levels, and preferably to 1.5 °C. The lawsuit had been filed in 2013 on behalf of almost 900 plaintiffs, including children. The court ordered the Dutch government to take action to lower domestic greenhouse-gas emissions by at least 25% by the end of 2020, compared with 1990 levels.

“People said we would have zero chance of winning,” says Jan Rotmans, a climate scientist at the Dutch Research Institute For Transitions in Rotterdam, who set up the Urgenda Foundation that filed the lawsuit. “But it turned out we were a catalyst.”

A court of appeal and the Supreme Court of the Netherlands later upheld the ruling. Emissions in the Netherlands in 2020 were down by around 24%, but missed the target; the Urgenda Foundation announced in June, after a meeting with Dutch Prime Minister Mark Rutte, that it is considering suing the government for damages resulting from insufficient climate action.

Similarly to subsequent rulings, the Dutch court’s move was heavily based on the body of climate science compiled by the Intergovernmental Panel on Climate Change (IPCC). In its judgment, the court cited scientific consensus that a global atmospheric concentration of carbon dioxide that was higher than 430 parts per million — the threshold to 1.5 °C warming — would mean “a serious degree of danger” for Dutch citizens, including extreme heat, drought, precipitation and sea-level rise.

“For the first time, a court had recognized that a government violates its duty of care for citizens if it doesn’t do enough to curb emissions,” says Joana Setzer, who specializes in climate litigation at the Grantham Institute and is a co-author of the July report. “This meant a lot from a legal point of view.”

Other cases have tended to follow the same scientific justification. Referring to IPCC science, judges in Ireland and Germany acknowledged that insufficient climate action might soon lead to disruptions — including wild weather or dangerous sea-level rises that would threaten the livelihood of future generations. In South Korea, a group of young people are challenging their government for human-rights violation on the same grounds. Judgments in that case and similar ones in the United States are still pending.

As signs of dangerous climate change are becoming more evident, pressure is mounting to hold governments and major carbon-emitting firms accountable. And this year has brought a string of weather extremes, including record heat in July in parts of North America, wildfires raging in Siberia and severe rainfall and floods in Belgium, Germany and China. Studies by Otto’s group and others have already demonstrated that climate change is at least partly responsible for the North American heatwave and the central European floods. Extreme weather events worldwide will become increasingly severe as temperatures continue to rise, the IPCC said in August, in the first part of its latest assessment of the state of climate science².

Bigger picture

The new IPCC reports will add pressure for stronger climate action, but as climate litigation expands in scope, it will draw on a broader range of research, says Peter Frumhoff, chief climate scientist at the Union of Concerned Scientists in Cambridge, Massachusetts.

“It’s a benefit to have the IPCC as a framework of accepted climate research,” he says. “But IPCC science isn’t all you need at court. There’s a lot more to the picture.” Future liability cases, says Frumhoff, could also incorporate the results of emerging attribution science, reviews of countries’ compliance with national commitments to the Paris agreement and studies related to what companies are doing in terms of the climate risks of their products.

There’s another reason that lawsuits might start to rely more on science that goes beyond what appears in IPCC reports. Those massive studies take years to compile, so the results can be out of date by the time the reports are released. Before this year, the last major IPCC report on the physical basis of climate science was published in 2013. Climate-change attribution was described as ‘challenging’ in a 2012 IPCC special report on managing the risks of extreme events and disasters³; but that science has matured to the point at which Otto and other researchers conduct attribution studies within days to weeks after major weather anomalies.

Yet judges are still reluctant to grant legal weight to attribution studies. A joint study by Minnerop, Otto and their colleagues, published in June⁴, found that such results are scarcely cited in climate lawsuits because of lingering doubts over the robustness of the findings. The IPCC’s latest report highlights that the methodology of climate-change attribution has matured since the last assessment, and that the results of state-of-the-art studies can now be considered robust.