Coverage of climate change in introductory biology textbooks, 1970–2019

These shifts reflect the increased rate of change in temperatures and weather patterns, and severity of risk. Organizations focused on solutions have more recently emphasized individ- ual, or grassroots, actions as drivers for political or industrial change. Examples include Article 12 of the Paris Agreement (2015) and founding of grassroots climate change organi- zations such as 350.org (2008), Project Drawdown (2014), and School Strike for Climate (2018). 4. The number of data figures referenced in the climate change passage will increase. An increase in the number of visual elements, especially those portraying data, corroborates statements presented in the text, promotes understanding and recall of climate change evi- dence, and increases the space devoted to the topic of climate change. Therefore, the num- ber of figures should reflect the value placed on the content. Materials and methods We used an intentional sample of the most widely used textbooks in U.S. undergraduate edu- cation. Gangwani and Landin determined that high-edition biology textbooks were represen- tative of a larger sample of textbooks, so our sample primarily included books with three or more editions [10]. Textbook selection We located 57 college-level introductory biology textbooks published between 1970 and 2019. We selected 1970 as the starting publication date to ensure detection of the earliest coverage, as a scientific consensus on global warming was reached in the 1970s [21]. Books written for different college audiences (science and non-science majors) were combined in our sample

since this separation is a recent phenomenon. Analyzed textbooks had three or more editions, except for two books published in the 1970s, as fewer textbooks reached high edition numbers during that decade. Giordano addresses this phenomenon as a reflection of societal factors, such as a substantial increase in the cost of textbooks, mergers among publishers, a backlash against textbooks in general, and removal of textbooks due to racial and gender bias or the per- ceived controversy of inclusivity [22]. Due to little coverage of climate change in this decade, we included low-edition textbooks to ensure a larger sample. To confirm that our sample of textbooks included those most often used in higher educa- tion, we contacted library reference desks at the three largest universities in the states of Cali- fornia, North Carolina, and Texas to request a list of textbooks used in their introductory biology courses. While the lists were limited to the past decade, all books had been included in our sample (see S1 Appendix). Passage selection The passage addressing climate change was located by searching for key phrases in the index: atmospheric carbon, changing climate, climate change, climate variation, environmental change, global warming, global climate, greenhouse effect, greenhouse gas, nuclear winter, ocean acidification, refrigeration effect, sea level rise, and warming climate. The search terms were chosen to account for various phrases used by experts over time, uncertainty in future

scenarios among earlier textbooks, and the use of alternative phrases to avoid social or political controversy. To limit the selection to anthropogenic climate change, we excluded passages that primarily focused on the carbon cycle, atmospheric composition, ozone depletion, photosynthesis, fluc- tuation of seasonal temperatures, or climate change events in past geologic eras. In most PLOS ONE Climate change in biology textbooks, 1970–2019 PLOS ONE | https://doi.org/10.1371/journal.pone.0278532 December 21, 2022 4 / 16