Such approaches translate well to the context of climate change litigation, and there is no loner any reason to regard 'causation' as a major obstacle to its success. Demonstrating that the actions of a particular defendant have, for example, 'materially increased the risk' of climate change damage occurring has been made significantly easier by: i) developments in the science allowing for the probabilistic attribution of specific climactic patterns and weather events to climate change; ii) the work of Rick Heede, showing that the majority of greenhouse gases can be attributed to just 90 'carbon majors'; and iii) the work of investigative journalists which appears to show that certain companies deliberately set out to undermine the scientific consensus regarding climate change, with the specific purpose of obstructing the development of appropriate policy responses. 6.6.2 Adapting the 'but for' test in cases of complex causation This section will review jurisprudence, which shows the 'but for' test may be adapted: a) in cases where there are different, cumulative causes for a single harm; or b) where it would be unfair or unreasonable to expect a claimant to establish a precise causal link. Material contribution to harm In Bonnington Castings Ltd v Wardlaw [1956] AC 613, [1956] UKHL 1 the UK's House of Lords held that it was sufficient to show that a defendant's breach of duty had made a material contribution to the claimant's injury even where other causes had made a more substantial contribution. 'Material', in this context, means a cause exceeding the de minimis threshold. The case provides, in small scale, an analogue for climate change litigation. The claimant had developed pneumoconiosis as a result of inhaling air containing minute particles of silica. The court found as fact that the defendant's breach of duty resulted in only a small proportion of the inhalation, which could not be precisely quantified. In the words of Lord Reid: The medical evidence was that pneumoconiosis is caused by a gradual accumulation in the lungs of minute particles of silica inhaled over a period of years. That means, I think, that the disease is caused by the whole of the noxious material inhaled and, if that material comes from two sources, it cannot be wholly attributed to material from one source or the other ... I cannot agree that the question is which was the most probable source of the Respondent's disease, the dust from the pneumatic hammers or the dust from the swing grinders. It appears to me that the source of his 31