Final answer:
In the disaster context mentioned, 'optimistic' generally refers to a hopeful or confident expectation regarding the future, which means the word is best defined as 'positive'.
Step-by-step explanation:
In the context of a disaster in Seattle, the word optimistic in paragraph 6 likely means positive. The passage provides various contexts hinting at the future outcomes or expectations, such as contingency plans in the face of threats, realistic scenarios for future warming, and the potential of post-fossil energy substitutes. Being optimistic generally involves a positive expectation or hopefulness regarding the future, despite the current challenges or threats that may exist. Therefore, the most appropriate answer is A) positive, as it suggests a hopeful or confident attitude towards the situation being discussed, unlike significant, specific, or unreasonable.