Feature: Air Pollution Litigation and the Problem of Causation

Dan Scott and Harry Little from Clyde & Co explore the difficulties of air quality litigation and how changes to causation rules could result in more successful claims. 

Air pollution is increasingly a source of liability risk. As in the climate change space, NGOs are actively seeking out strategic litigation opportunities and identifying novel means of bringing claims against both public and private bodies. Litigation is brought with a dual purpose: to hold polluters to account and influence their behaviours in future.  

Presently, air quality litigation is focused on public bodies, insisting that they do more to regulate and enforce pollution reduction measures. In the coming years we expect to see an increasing number of claims brought against private bodies, including primary polluters and the manufacturers of allegedly polluting products. Such claims will test the boundaries of environmental law.  

One question is whether polluting conduct can be characterised as a breach of legal duty. The answer to this question may seem obvious, but the main activities causing air pollution – driving cars and heating homes – are undertaken by all of us as a core part of our daily lives. A similar point applies to the manufacturer of products which cause air pollution. If a car or domestic boiler complies with current standards, can it amount to a breach of duty to place it on the market? 

There are also difficulties of proof and causation. There is a factual aspect: how to prove and quantify the impact of a single defendant’s activities among many other causes of local air pollution. Polluting gases may travel many miles and persist in the local atmosphere for varying periods of time. The effect is not always linear: human activity, natural phenomena and climatic conditions may contribute to spikes in local pollution.  

There is also a legal aspect. A prospective claimant will need to prove the existence of a substantial link between the defendant’s conduct and injury, and show that the injury is not too remote a consequence of the defendant’s wrongdoing. 

cars passing through north and south

If one considers a claim being made by residents of a town for bodily injuries they allege are caused by emissions from a local factory, the difficulty in establishing causation becomes immediately apparent. In such a scenario, one must consider:  

  • pollutants emitted from the factory; 
  • pollutants travelling in the air from outside the relevant locality;  
  • pollutants from stationary emitters, including households, businesses, and other factories;  
  • pollutants from mobile or transient emitters such cars, trains, aircraft; and 
  • the length of time over which the pollutants have caused or contributed to the injury.  

Assume, for example, that the factory contributed 50% of the local emissions, should that be sufficient to satisfy the requirements of causation? The claimants will say that the factory was the most substantial contributor to air pollution and should be held to account. The defendant will argue that it cannot be held liable when there were so many other contributing causes. Both positions have merit. There is something counterintuitive about a defendant escaping liability simply because other people were engaged in the same harmful behaviour. It would, however, be equally counterintuitive to allocate 100% liability to a company which only contributed 50% of local emissions.  

Material Contribution 

In England and Wales the courts have shown a willingness to depart from strict causation analysis where there is a pressing public policy consideration. In certain circumstances, the courts have used the test of ‘material contribution’ wherein a claimant need show only that the defendant’s actions materially contributed to the injury.  

In the well known case of Fairchild v Glenhaven, the House of Lords considered a difficult case involving mesothelioma. The claimants had been exposed to asbestos throughout their working lives and while working for different employers. As they could not prove during which period of employment the harm occurred, the employers argued that none of them could be held to account. The Court held that, exceptionally, the need for common sense should prevail over the strict requirements of causation, and therefore the employees could recover compensation from any employer who had materially contributed to the risk of harm.  

According to the Fairchild approach, the claimant must show that the defendant’s conduct was at least capable of causing or aggravating the damage, and that it did in fact materially increase the risk of that damage.  

It is important to stress that the Fairchild approach has not yet been adopted outside the narrow context of employers’ liability claims. Extending it to environmental cases would be a novel and unprecedented development. The approach would not necessarily lead to a just outcome. Building on the above example, consider what would happen if the residents of the town brought their claim against a group of car manufacturers due to there being substantial emissions emanating from the motorway running through the town. Whilst the individual manufacturer’s contribution to the local emissions may well have materially contributed to the residents’ injuries, it does not seem just that a single manufacturer whose products only contributed to a small % of local emissions could be held liable for the totality of the injury.  

Alternative Theories  

There are other theories of causation which claimants might invoke. Each of those theories would have its own issues in the context of air pollution, but may be a more or less attractive alternative to traditional rules.  

In the FCA Business Interruption Test Case, the Supreme Court deviated from traditional causation rules, finding that each and every occurrence of Covid-19 was a separate but equally effective cause of the Covid-19 regulations imposed by the British government.  

In the US, the court have developed a ‘market share’ theory of causation following the landmark product liability case of Sindell v Abbott Laboratories. There, a claimant had been injured by a drug but could not establish which company had manufactured the drug. The California Supreme Court found each manufacturer of the drug liable for a percentage of the plaintiff’s damages based on its market share of the drug production. 


On the application of current rules, civil claims for harm arising from poor air quality are destined to fail. It is almost impossible to prove that any single emitter was the cause of harm. Nevertheless, the common law is not written in stone, and changes to the way in which courts apply causation rules could have a substantial effect on the outcome of claims. In the coming years we expect to see some new and challenging cases in this important field.  

This article first appeared in the May issue of Air Quality News – read it in full here

Photo by Alexander Popov


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