Attribution science and the law

Introduction

The scientific consensus on human-caused climate change is no longer in doubt. What is evolving rapidly is the ability to trace specific harms such as sea level rise, heatwaves and wildfires back to human activities. This growing field, known as attribution science, is playing a pivotal role in climate litigation. The recent decision in RWE -v- Lliuya marks a turning point: courts have accepted that emissions from a specific company can be a causal link in real-world climate impacts.

This article explores the scientific foundations of attribution science, its implications under tort law, particularly nuisance, and how it is reshaping climate accountability.

A brief history of climate science

The idea that excess greenhouse gases could warm the planet dates to 1856, when American scientist Eunice Newton Foote found that a glass cylinder filled with CO₂ heated more quickly than one filled with regular air. In 1890, Swedish chemist Svante Arrhenius quantified how changes in atmospheric CO₂ could drive global temperatures.

By 1938, engineer Guy Callendar showed that Earth had already warmed by 0.5°C since 1890. And in 1959, nuclear physicist Edward Teller, better known as the father of the hydrogen bomb, warned that: 

"It has been calculated that a temperature rise corresponding to a ten percent increase in carbon dioxide will be sufficient to melt the ice cap and submerge New York.” 

At the time, CO₂ levels were 317.7 ppm, already a 13% increase from pre-industrial levels. Today, they exceed 430 ppm.

Radiative forcing: a system out of balance

In that same 1959 speech, Teller explained what we now call radiative forcing: CO₂ allows solar radiation in but blocks outgoing heat. This imbalance of ingoing and outgoing energy in the form of heat forces the Earth’s system to adjust, primarily by warming, an expression of the first law of thermodynamics: energy cannot be created or destroyed, only transferred.

In 2021, satellite data confirmed this imbalance, providing direct evidence that human activity is altering Earth’s energy system. There is now a measurable, causal link between human emissions and planetary warming.

Cause and effect: the rise of attribution science

Extreme weather events have always occurred - hurricanes, droughts and monsoons are part of natural variability. But a changing climate system can influence the severity of these events. In other words, while the number of events might not increase dramatically, the intensity and impact of those events are amplified. Climate change acts as a risk multiplier.

For example, melting ice caps increase the volume of water in the oceans, which can lead to heavier rainfall and more severe flooding. Higher temperatures accelerate evaporation, drying out soils and vegetation, which in turn increases the likelihood and intensity of wildfires.

In 2004, a paper titled Human Contribution to the European Heatwave of 2003 marked a turning point. Using updated climate models that incorporated radiative forcing, researchers compared two scenarios:

• One in which atmospheric CO₂ remained at pre-industrial levels called a ‘counterfactual world’.

• One using actual greenhouse gas concentrations as they increased over time.

By comparing these two models, the researchers were able to determine how much climate change had increased the likelihood of the heatwave. The result: climate change had doubled the probability of the event. This was the first major application of what is now known as attribution science.

The limits—and power—of attribution

Attribution science is more reliable for chronic events like heatwaves or sea level rise than for short-term more localised incidents like flash floods. But even with uncertainty, the ability to quantify risk increases and strengthens the legal case for accountability.

Even with improved modelling, there are still uncertainties about how severe the upper extremes will be – or possible worst-case scenarios. But these uncertainties don’t weaken the case for action; they strengthen it. Understanding the range of possible futures is key to preparing for them, and to assigning responsibility when harm occurs.

Attribution science in the courts

The impacts of climate change we’re experiencing today aren’t the result of emissions released yesterday. They’re the result of the climate system itself, and how it continues to respond to the excess greenhouse gases already in the atmosphere. Today’s actions are about limiting the damage still to come. 

But the damage already happening and the losses being incurred? That’s where attribution science comes in.

Whether it’s rebuilding after floods, compensating for lost farmland or addressing deaths from extreme heat, such as in the 2021 wrongful death case due to the Pacific Northwest heat dome, attribution science makes it possible to connect human-caused emissions to real-world harm.

Nuisance law and the good neighbour principle

Nuisance law governs how individuals use their property without unreasonably interfering with others. A private nuisance doesn’t require intent—only that the interference is substantial and foreseeable. Many jurisdictions, including England & Wales, USA, Canada, New Zealand, France, Germany and Brazil recognise nuisance-based liability.

In a shared climate system, emissions from one country affect others globally. This expands the traditional concept of a ‘neighbour’. The principle of not unreasonably interfering with others now applies across borders.

RWE -v- Lliuya: a legal turning point

In this case, a Peruvian farmer sued German energy giant RWE, claiming its emissions contributed to melting glaciers above his town, raising flood risk. Although on appeal the case was dismissed by the High Regional Court of Hamm due to insufficient imminent risk, the key takeaway was that the court accepted that climate science could establish a causal link.

As Grantham Institute Research Fellow Noah Walker-Crawford noted:

"This ruling sets a significant precedent... It recognised that emissions from a specific company may be linked to real-world climate impacts.”

A global legal landscape

The principles in RWE -v- Lliuya: causation, foreseeability and unreasonable interference, exist in many legal systems. In England and Wales, private nuisance requires substantial interference with property rights, not negligence. Claims can be based on continuing harms from past acts—crucial for climate cases.

And while the UK has a Polluter Pays Principle enacted in the Environment Act 2021, there have been no significant criminal prosecutions under it. That may be because companies can now offer enforcement undertakings which are a voluntary commitment to remedy environmental harm as an alternative to criminal prosecution. This may be why the tort of nuisance will be the next battlefront for environmental claims. 

This opens the door to similar lawsuits in the US, Canada, Australia and elsewhere. Climate litigation is becoming a global phenomenon, mirroring the global nature of emissions.

New tools for accountability

Technologies like Climate TRACE are transforming litigation. Using satellite data and AI, Climate TRACE tracks emissions from individual facilities in near real-time.

This allows plaintiffs to link harm to specific emitters, strengthens evidentiary chains, and enables courts to assess proportional responsibility. For companies, it signals that accountability is now trackable.

Conclusion: from science to litigation

Attribution science has moved the climate conversation from “Is it happening?” to “Who is responsible?” It enables courts to link emissions to impacts—and to assign liability.

As more cases test these links and data tools become more sophisticated, tort law—especially nuisance—will play a key role in climate accountability. We all live in the same atmosphere. The question now is not whether harm is occurring, but who should pay for it—and whether the law is ready to act.