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

count of one-half point. We did not include descriptive figures, such as a photograph of an impacted animal or an infographic showing how greenhouse gases block infrared energy from leaving the atmosphere, in the data figure count. Intercoder reliability Each author coded each textbook separately. Agreement for each data entry was defined as the same score for numbers under 10, or scores within ±1 for counts of 10 and above. We used a simple percent agreement due to the large number of possible categories. Agreements of 90% or higher were considered acceptable [24]. For any book with an intercoder agreement of less than 90%, the authors recoded the passage together. In almost every instance, 100% agreement was attained though discussion and consensus; for the few data points without agreement, we averaged the two scores. Results Our data indicate that climate change coverage changed substantially over time, the greatest shift occurring in the 1990s. Modifications to content since 2000 have been minor and empha- size the impacts of climate change while deemphasizing solutions. Amount of content Coverage of climate change in textbooks increased from 1970 to 2019, though not consistently or relative to scientific research or the severity of the issue. Prior to 1990, the textbook passage addressing climate change averaged fewer than 11 sentences. In the 1990s, coverage expanded to almost 40 sentences, a 264% increase. However, two outliers with large passages, at 90 and 108 sentences, were two editions of the same book. The median content during this decade

was 30 sentences. The following decades increased the average climate change content from 51 sentences in the 2000s to 67 sentences in the 2010s. The decade spanning 2010 to 2019 also showed a large range, with books presenting between 22 and 107 sentences. The median length of the passage dropped from 52 sentences in the 2000s to 45 sentences in the 2010s (Fig 1). The coverage of climate change in textbooks has decreased compared to the number of scien- tific articles published after the 1990s. In the 1990s, there was approximately one textbook sen- tence for every 200 scientific publications about climate change. In the 2010s, the ratio was one textbook sentence for every 1,100 scientific publications (Fig 2A). Textbook coverage has remained proportional to global temperatures. In the 1990s, there was approximately one text- book sentence for each 0.01˚ Celsius increase in global temperature. Since 2000, the textbook content decreased slightly in comparison to global temperatures, although the median number of sentences in the 2010s dropped to almost half the temperature anomaly (Fig 2B). The years 2015–2019 show a notable increase in global temperatures. The average number of textbook sen- tences would need to increase by 23 sentences to remain in proportion to these temperatures. Start location of climate change passage Climate change coverage has been consistently presented at the end of biology textbooks. Small shifts in placement over time have moved the topic further toward the end of the book.

The earliest start location, at a median of 85.3% of the book, occurred in the 1970s. The latest start location, at a median of 97.6%, appeared in textbooks published in the 2010s (Fig 3). Only four textbooks, published between 2002 and 2014, contained multiple passages addressing cli- mate change. We averaged the start locations, which remained toward the end of the book at 85.6%. PLOS ONE Climate change in biology textbooks, 1970–2019 PLOS ONE | https://doi.org/10.1371/journal.pone.0278532 December 21, 2022 6 / 16