Fewer than 100 firms worldwide are recognised by Bloomberg to report accurate greenhouse gas emissions. Yet, tens of thousands of people are talking and tweeting about climate change every day. How can this attention be converted into accurate action? We propose that sustainable data science might help, specifically that ‘emotional nowcasting’ of societal responses to sustainability related statements as expressed on Twitter. First, we differentiate between various types of corporate sustainability performance data and highlight the challenge that corporate greenwashing and a potential lack of financial independence of the assessor from the assessed poses for these data sets. Second, we introduce the concept of emotional nowcasting with two case studies of an emotionally non-ambivalent context, the football matches England vs. Germany and England vs. USA at the 2010 world cup. These case studies serve as a proof of concept for emotional nowcasting. Finally, we discuss the potential for emotional nowcasting to mitigate the pandemic of greenwashing currently experienced in sustainability communication. We conclude that emotional nowcasting can serve as one test of greenwashing which is on its own though not necessarily sufficient.