The decision to drop textbooks that question the severity of climate change from schools in Portland, Oregon, has drawn heavy criticism from the National Coalition Against Censorship (NCAC), which is warning that it will “undermine public education”.

Following lobbying from environmental groups, which had criticised science textbooks expressing doubt about “the human causes and urgency of the crisis”, and which use words such as “might”, “may” and “could” when referring to climate change, last month the Portland Public Schools board voted to “abandon the use of any adopted text material that is found to express doubt about the severity of the climate crisis or its root in human activities”.

The move drew criticism from conservative quarters, with Fox News quoting one commenter saying: “I have never seen a case for homeschooling more clearly put forward. This is further proof that public schools are not interested in education, only political indoctrination.” Commenters on Glenn Beck’s site the Blaze, meanwhile, compared it to book-burning.

The move has now raised “serious concerns” at free-speech organisation NCAC, which released a statement condemning the decision “for all its good intentions”.

“Social studies texts accurately describing the political debate around fossil fuels and climate change, for instance, would presumably contain comments from individuals who ‘express doubt about the severity of the climate crisis’. If such material is excised from the curriculum, will students be prepared to face – and argue with – climate-change denial when they encounter it in the world outside school?” asked the NCAC.

“Purging the curriculum of this kind of material will undermine public education, which should equip students for critical and informed consideration of important matters of public policy and controversy,” the statement continues. “Even if some scientists questioning the human causes of climate change do so apparently at the behest of the fossil fuel industry, it is still a fact that environmental policy is a subject of ongoing debate. Students should be conversant with, and equipped to address, the various questions and issues that are the subject of public discussion.”

The NCAC adds that “curricular decisions that appear to be a result of political pressure are suspect, no matter from which political side the pressure comes”, and is adamant that “deciding how to approach the existing political debate around the causes of climate change should be left to those who teach about it”.