this study, targeting on hashtags is more in line with our research question. Firstly, hashtags were
invented spontaneously by users of Twitter in 2007 as a mechanism to categorize discussions [ 74].
Words with hashtags are recognized as topics and considered worthy of public discussion. Secondly,
by attaching # to certain words in tweets, the users intentionally anchor their tweets to certain topics.
The operator # explicitly reﬂects the author’s emphasis, which can help us extract rather than infer the
author’s identiﬁcation of the topic of the tweets. Our research question is to analyze and visualize
the associations of topics in public climate discourse. Compared with other approaches, analyzing
hashtags co-occurrence pattern has advantage in extracting the structure of public discussions.