Increasing global temperatures influence human behavior in numerous ways. Recently, a new study sheds light on a crucial aspect of the issue: extremely hot days correlate with heightened negative emotions, as revealed by a comprehensive analysis of social media content.

In total, the research scrutinizes 1.2 billion social media contributions from 157 nations over the course of a year. The findings indicate that when the temperature exceeds 95 degrees Fahrenheit (or 35 degrees Celsius), expressed feelings tend to become around 25 percent more negative in low-income nations and approximately 8 percent more negative in higher-income nations. Intense heat impacts individuals emotionally, not merely on a physical level.

“Our research demonstrates that rising temperatures threaten not only physical health and economic output — they also influence emotional states globally, every day,” explains Siqi Zheng, a professor in MIT’s Department of Urban Studies and Planning (DUSP) and Center for Real Estate (CRE), and a co-author of the paper detailing these findings. “This work paves the way for a new understanding of how climate stress is shaping human well-being on a global scale.”

The paper, “Unequal Impacts of Rising Temperatures on Global Human Sentiment,” is released today in the journal One Earth. The authors include Jianghao Wang from the Chinese Academy of Sciences; Nicolas Guetta-Jeanrenaud SM ’22, a graduate of MIT’s Technology and Policy Program (TPP) and the Institute for Data, Systems, and Society; Juan Palacios, a visiting assistant professor at MIT’s Sustainable Urbanization Lab (SUL) and an assistant professor at Maastricht University; Yichun Fan from SUL and Duke University; Devika Kakkar of Harvard University; Nick Obradovich from SUL and the Laureate Institute for Brain Research in Tulsa; and Zheng, who holds the STL Champion Professorship in Urban and Real Estate Sustainability at CRE and DUSP. Zheng is also the faculty director of CRE and established the Sustainable Urbanization Lab in 2019.

Social media as a lens

For the analysis, the researchers examined 1.2 billion posts from social media platforms Twitter and Weibo, all from 2019. They employed a natural language processing method called Bidirectional Encoder Representations from Transformers (BERT) to analyze 65 languages across the 157 countries included in the study.

Each social media post received a sentiment score ranging from 0.0 (indicating very negative content) to 1.0 (indicating very positive content). The posts were geographically aggregated to 2,988 locations and assessed in relation to local weather conditions. This approach enabled the scholars to ascertain the link between extreme temperatures and expressed sentiments.

“Social media data offers us an unparalleled insight into human emotions across various cultures and regions,” Wang asserts. “This method enables us to quantify the emotional impacts of climate change at a scale that traditional surveys simply can’t match, providing real-time insights into how temperature influences human sentiment globally.”

To evaluate the effects of temperature on sentiment in different income contexts, the researchers also referenced a World Bank threshold for gross national income per capita set at $13,845, discovering that in regions with incomes below this level, the impact of heat on emotions was three times greater than in more affluent areas.

In the long run

Utilizing long-term global climate models while anticipating some adaptation to heat, the researchers also generated a long-term forecast of the impacts of extreme temperatures on sentiment by the year 2100. Extending their current findings to that timeframe, they project a 2.3 percent deterioration in emotional well-being due to high temperatures alone by then — though this is a speculative estimate.

“It’s evident now, as our current research contributes to earlier findings, that weather influences sentiment on a global scale,” Obradovich states. “And as weather patterns and climates evolve, ensuring individuals can become more resilient to disruptions in their emotional states will be a critical component of overall societal adaptation.”

The researchers acknowledge that there are many complexities involved in this topic, and ample opportunity for additional inquiry in this realm. One consideration is that social media users may not perfectly represent the broader population, with young children and the elderly likely less active on social media compared to others. However, as the researchers note in the paper, these very young and elderly individuals are probably especially susceptible to heat shocks, potentially making their reactions to extreme temperatures even larger than what their study can account for.

This research is part of the Global Sentiment project led by the MIT Sustainable Urbanization Lab, and the dataset from the study is publicly accessible. Zheng and the other co-authors have explored these dynamics using social media in the past, but never at such a large scale.

“We hope this resource assists researchers, policymakers, and communities in being better equipped for a warming world,” Zheng concludes.

The research received support, in part, from Zheng’s endowed professorship research fund, along with grants that Wang obtained from the National Natural Science Foundation of China and the Chinese Academy of Sciences.