Memorandum for the Petitioners | 40 5.31. Extreme event attribution can assess the increased likelihood of a specific extreme weather event occurring. Attribution studies for cyclones, including typhoons and hurricanes, link additional flooding from rising sea levels to human-induced climate change, as well as how warmer ocean temperatures sustain and intensify a hurricane and assess increases in the precipitation.'°° Tropical storms have also been the subject of extreme event attribution studies. Studies attempt to determine whether human GHGs have made an extreme event more intense (ie., caused more rainfall or made temperatures hotter), or more likely to occur (ie., increased the chance or likelihood of the extreme event).!36 5.32. The results are expressed probabilistically -- in the same way that risk factors in health are measured -- because, in theory, any extreme event is possible in the counterfactual world. Scientists have, therefore, said that it is not possible to give a simple yes or no answer to the question of whether a particular event was caused by climate change; rather, what can be measured is how global warming made the event more intense, or more likely to occur. This methodology, however, does not imply that there is no relationship between cause and effect; it simply expresses the relationship in a statistical form.!3” 5.33. In the case of super typhoon Haiyan, Summary of the Amicus Curiae: as stated in the Joint The ocean heat content (OHC) and sea level in the region had increased a great deal since 1993 and especially since 1998. Consequently, as the typhoon approached the Philippines, it was riding on very high sea surface temperatures (SSTs) with very deep support through the high OHC, and the strong winds and ocean mixing did not cause as much cooling as would normally be experienced, probably helping the storm to maintain its tremendous strength. Moreover, the storm surge was without a doubt exacerbated considerably by the sea levels, which were some 30 cm above 1993 values. Although natural variability played a major role, there was also a global component through increased OHC from the Earth’s energy imbalance. 38 (Emphasis supplied) 5.34. As explained by amicus expert Dr. Kevin Trenberth, Distinguished Senior Scientist at the National Center for Atmospheric Research, “the changes in extremes have huge impacts on society and on ecosystems and the environment (....) In one sense, the extreme event '85 See Exhibit “EEEEEEE” to “EEEEEEE-3,” Statement of Brenda Ekwurzel, dated 20 September 2018, p. 3. '86 See Exhibit “DDDDDD” to “DDDDDD- 15,” Statement of Sophie Marjanac, dated 03 August 2018, pp. 4-5, par. 14, (in-text citations omitted). '37 Ibid., pp. 5-6, para. 17 (in-text citations omitted). '88 Joint Summary of the Amicus Curiae, supra note 50, p. 38 (in-text citations omitted).