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Ambiguous language on climate change in American textbooks is said to be fuelling the mood of climate denial according to a study Mario Tama/Getty

Climate change is possibly happening, humans may or may not be causing it, and it is unclear if we need to take immediate mitigating action, sum up dubious messages emanating from science textbooks in the US.

While, only 54% of American teens believed climate change is happening, around 43% believe it is caused by humans, while 57% are not concerned about it, a large part of the blame goes to these textbooks.

A new study measuring how four sixth-grade science textbooks, adopted for use in California, found climate change offered to students as a controversial debate. Prolific use of verbs like "could", "may" or "might" accentuate the uncertainties behind climate change, while words such as "find", "determine", "measure" and "obtain" are less frequently used. The most frequently used word associated with scientists was "think".

In fact, some "positive" results of climate change also creep into the books: "Global warming could have some positive effects. Farmers in some areas that are now cool could plant two crops a year instead of one. Places that are too cold for farming today could become farmland."

"We found that climate change is presented as a controversial debate stemming from differing opinions," said Diego Román, an assistant professor in the Department of Teaching and Learning, Southern Methodist University, Dallas, a co-author of the study. "Climate skeptics and climate deniers are given equal time and treated with equal weight as scientists and scientific facts -- even though scientists who refute global warming total a miniscule number."

Scientists are in agreement over the issue of climate change as well as the human hand tampering the climate, note the researchers. The most recent report from the Intergovernmental Panel on Climate Change, using the evidence of 600 climate researchers in 32 countries in 2013 stated "human influence on the climate system is clear".

Mind your language

As a social scientist who studies linguistics and the impact of words, Román said language matters, particularly in the textbooks in the nation's three most populated states, California, Texas and New York, which set standards for the rest of the country.

He was also critical of the fact that the textbooks did not call upon the students to act to mitigate climate change. A generic advice such as "take care of the environment" or "stop burning coal and wood," is not as effective as drawing connections between climate change and the need to turn off lights or drive less.

The researchers examined different textbooks, each published in either 2007 or 2008 by a different major publisher. They found ambiguous language in the books calling climate change as unsettled science, much like what the media has portrayed.

The textbooks misrepresented actual scientific discourse which asserts the risk carried by climate change and the need for action, besides stressing the human cause, said the authors.

As states adopt the new national standards for science education developed in part by the National Science Teachers Association and the American Association for the Advancement of Science, there is an opportunity to set right the misleading language on climate change, the researchers noted.

The textbook researchers recommend against stripping out uncertainty, but suggest clarifying what exactly is unknown and why. They also recommend the inclusion of humans as agents and as the cause of climate change.

The findings were published in the Environmental Education Research journal in the article, "Textbooks of doubt: Using systemic functional analysis to explore the framing of climate change in middle-school science textbooks."