Major textbooks used in California middle schools do not accurately portray climate change or the science behind it, describing it as a debate, not a fact, according to a Stanford University study.

Researchers analyzed four textbooks published almost 10 years ago that are commonly used in sixth grade classes, the first year that California students learn about climate change.

“We found that through language choices, the text portrayed climate change as uncertain along several lines, such as whether climate change was happening, whether humans were causing it and what the effects will be,” K.C. Busch, one of the paper’s co-authors and doctorate candidate at the Stanford Graduate School of Education, said in a statement about the research.

Busch said that textbooks typically use declarative language, but in sections on climate change, the books used words like “could” and “might.”

One of the books analyzed, Prentice Hall’s “Focus on Earth Science” described climate change this way, according to the study: “Not all scientists agree about the causes of global warming. Some scientists think that the 0.7 Celsius degree rise in global temperatures over the past 120 years may be due in part to natural variations in climate.”

“While uncertainty is inherent in science, in this case, the text is not scientifically accurate,” Busch said in the statement.

Busch said that while there is political debate surrounding climate change in the U.S., textbooks need to describe the science behind climate change accurately.

“I think the textbook adoption process is one that is social and political. I imagine that textbook publishers have to ‘toe the line’ in order to both meet the state science standards and have their book be palatable to a wide range of political ideologies,” she said in the statement. “With that said, however, the science in the science textbook should be accurate. There can be societal debate as to what we should do about climate change, but continuing to portray a scientific debate is dishonest.”

In a statement to The Guardian, Pearson, the company that owns publisher Prentice Hall, said that the company is committed to balance and accuracy.

“Pearson curriculum is developed by expert author teams and is reviewed by independent, academic reviewers,” a spokesman told The Guardian. “We always are committed to presenting balanced, unbiased, and accurate material, and welcome the opportunity to meet with parents and educators to listen to their concerns about textbook content.”