tortious, or whether they were man-made: The purpose of the Fairchild exception is to provide a cause of action against a defendant who has materially increased the risk that the claimant will suffer damage and may have caused that damage, but cannot be proved to have done so because it is impossible to show, on a balance of probability, that some other exposure to the same risk may not have caused it instead. For this purpose, it should be irrelevant whether the other exposure was tortious or non-tortious, by natural causes or human agency or by the claimant himself. These distinctions may be relevant to whether and to whom responsibility can also be attributed, but from the point of view of satisfying the requirement of a sufficient causal link between the defendant's conduct and the claimant's injury, they should not matter. It was, however necessary to prove that the type of risk to which the defendant contributed was in fact a cause of the injury: In my opinion it is an essential condition for the operation of the exception that the impossibility of proving that the defendant caused the damage arises out of the existence of another potential causative agent which operated in the same way. It may have been different in some causally irrelevant respect, as in Lord Rodger's example of the different kinds of dust, but the mechanism by which it caused the damage, whatever it was, must have been the same. So, for example, I do not think that the exception applies when the claimant suffers lung cancer which may have been caused by exposure to asbestos or some other carcinogenic matter but may also have been caused by smoking and it cannot be proved which is more likely to have been the causative agent. Adopting such an approach to the context of climate change implies a two stage test for 'causation': 1 The Claimant must prove, on the balance of probabilities, that climate change was a cause of the particular injury; and, if so, that 2 That the Defendants actions or omissions have materially increased the risk of climate change. The Court in Barker, however, preferred to avoid the 'legal fiction' that the test was one of causation. Rather there were circumstances in which risk creation could displace the requirement to prove causation (Lord Scott at para. 53): It is essential, in my opinion, to an appreciation of the effect of the Fairchild decision to keep firmly in mind that liability was not imposed on any of the defendant employers on the ground that the employer's breach of duty had caused the mesothelioma that its former employee had contracted. That causative link had not been proved against any of them. It was imposed because each, by its breach of duty, had materially increased 43