Crisis events can be important triggers for social action. In the context of digital activism, however, this linkage has been largely disregarded. Using two Twitter datasets from the Australian 2019-2020 "Black Summer" bushfires and the 2020-2021 bushfire season, we empirically explore how social media discussions about these crises eventually lead to digital activism against man-made climate change. By employing a combination of different topic modeling techniques and a thematic analysis, we find that discussions about climate change spiked in five out of six communication peaks related to bushfire events. These discussions, analyzed based on recommendations from Computationally Intensive Theory Construction (CITC), reveal three main themes—highlighting, debating, and mobilizing—which constitute the transition between crisis communication and digital activism in these cases. This pattern extends existing research by showing how crises can trigger digital activism and contributes to a better theoretical understanding of the early stages of digital activism. Moreover, our study supports practitioners in moderating social media discussions around socially sensitive crises.