  Characterising the spreading of ideas within echo chambers is essential for
understanding polarisation. In this paper, we explore the characteristics of
popular and viral content in climate change discussions on Twitter around the
2019 announcement of the Nobel Peace Prize, where we find the retweet network
of users to be polarised into two well-separated groups of activists and
sceptics. Operationalising popularity as the number of retweets and virality as
the spreading probability inferred using an independent cascade model, we find
that the viral themes echo and differ from the popular themes in interesting
ways. Most importantly, we find that the most viral themes in the two groups
reflect different types of bonds that tie the community together, yet both
function to enhance ingroup connections while repulsing outgroup engagement.
With this, our study sheds light, from an information spreading perspective, on
the formation and upkeep of echo chambers in climate discussions.
