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

textbooks, headings marked the start and end of the passage; however, in earlier textbooks, the passage transitioned without a delineating header. Occasionally, a climate change passage incorporated non-relevant topics (e.g., the carbon cycle or photosynthesis). Since these sen- tences were within the delineated passage, we included them in our counts, which inflated the length of the passage. Rarely were anthropogenic climate change and the greenhouse effect addressed in multiple locations within the book. In these instances, we averaged the two start pages and coded the selections separately, though data were combined for processing. This sit- uation inflated the length of the passage since the descriptions of climate change were repeated in each section. Text outside the main passage (e.g., a side panel) was included if it contained at least three paragraphs. We counted shorter passages only if there was no other content, as was often the case for textbooks published in the 1970s. Climate change content was often included in side- bars or supplemental page panels in 1980s textbooks. To calculate the start location as a percentage of the books’ total pages, we used the last page of the last chapter since appendices, indices, and glossaries varied substantially between books and over time. In the case that a textbook contained no passage related to climate change, we excluded that book from the start-page average. Text analysis Sentences within the climate change passage were counted and categorized. We included only

the main body of the text; we did not include figure captions, review questions, lists of learning objectives, chapter summaries, scientist biographies, or footnotes. We also did not count rhe- torical questions (i.e., “How does this happen?” or “Why?”) since these inflated the number of sentences without addressing content. Sentences within parentheses were not included, as they usually referred to other content or chapters. Each sentence was classified into one of three broad categories: 1) a general description of the greenhouse effect, 2) impacts of climate change, or 3) actions that ameliorate the effects of climate change. Sentences addressing the impacts of climate change were further delineated into nine subcategories: 2a) sea level, glaciers, or polar ice; 2b) rainfall or drought; 2c) extreme weather events (e.g., hurricanes, wildfires, el niño); 2d) temperature changes; 2e) species extinction or range shifts; 2f) agricultural impacts; 2g) ocean acidity or currents; 2h) human health; and 2i) “other.” Some sentences addressed two or three subcategories; in this case we placed a portion of one point in each of the addressed subcategories. If a single sentence included more than three subcategories, we tagged it as “other.” Also, action sentences were further divided into 3a) individual/local actions or 3b) national/international actions. Rarely did a text include generalized or vague sentences addressing solutions; we categorized these as “other.” Individual actions were further categorized as high-impact (e.g., reproductive plan-

ning, transportation, diet choices) or low-impact (e.g., recycling, turning off lights) for reduc- ing carbon emissions, according to Wynes and Nicholas [23]. Figure analysis Any data figures, tables, charts, or graphs referenced in the text passage were included in the analysis (hereafter referred to as figures). Data categories included global temperatures, carbon dioxide levels, sea level change, species movement (often maps), and photographic evidence (e.g., comparison in size of glaciers over time), or “other” (e.g., agricultural yields, changes in rainfall). If a single figure depicted multiple data categories, we included a portion of one point in each of the addressed categories. For example, many textbooks included a graph showing the rise in CO2 levels and global temperatures over time. In this case, each category received a PLOS ONE Climate change in biology textbooks, 1970–2019 PLOS ONE | https://doi.org/10.1371/journal.pone.0278532 December 21, 2022 5 / 16