The struggle over what American students learn about global warming is heating up as conservative lawmakers, climate change doubters and others attempt to push rejected or debunked theories into the classroom.
An overwhelming majority of climate scientists say manmade emissions drive global warming, but there's no such consensus among educators over how climate change and its causes should be taught.
Several U.S. states recently considered measures allowing or requiring teachers to present alternatives to widely accepted viewpoints on such topics. For example, a stalled proposal in Iowa would have required teaching "opposing points of view" on topics such as global warming, and proposed science standards in Idaho would have students taught that human impact is driving global warming and that natural factors also contribute.
The debate is arriving on teachers' doorsteps nationwide, as thousands are being mailed the book "Why Scientists Disagree about Global Warming" from a Chicago-area advocacy group called The Heartland Institute that challenges the assertion that there is consensus about a human-caused climate crisis. In a follow-up statement, the institute's president said science instructors should "keep an open mind" and shouldn't teach "dogma pushed by some environmental activist groups."
The National Center for Science Education made rebuttal flyers explaining that Heartland relies on debunked theories. The National Science Teachers Association dismissed the mailing as propaganda and urged educators to recycle the books.
Meanwhile, President Donald Trump's decision to withdraw the United States from an international agreement aimed at curbing global warming is reinforcing some teachers' sense of urgency about discussing humans' role in accelerating climate change.
"This isn't just something we're talking about because it's going to be on the test," said Jim Reding, a high school teacher in Granville, Ohio, who said he wants his students to think critically and have civil, reasoned conversations on the topic. "This is something that could have an impact on my life or my children's life going forward."
An NCSE survey released last year of 1,500 public middle- and high-school science teachers found about three-quarters taught something about climate change during the 2014-15 school year. About a quarter give equal time to "perspectives that raise doubt about the scientific consensus," the survey found.
Approaches to teaching climate science depend largely on state science standards and decisions by districts and instructors, because the federal government doesn't dictate curriculum, said Glenn Branch, deputy director of the science education center. Many schools teach climate change in some way, but teachers vary in knowledge of the topic and how much they emphasize human impact, he said.
Lawmakers in Alabama and Indiana recently passed resolutions in support of giving teachers' latitude in how they help students analyze and critique scientific theories. Bills to put similar allowances into law fizzled in Oklahoma, South Dakota and Texas.
Florida lawmakers approved making it easier for people to challenge textbooks as inappropriate, and critics argued that bill could lead to schools removing books that discuss climate change.
The executive director of the science teachers association, David Evans, criticizes such measures as efforts to introduce theories that aren't evidence-based.
It's "permission, or in some cases even an imperative, to talk about things which are not scientific in the science classroom," he said. "And we firmly oppose that."
But the South Dakota bill's primary sponsor, Republican Sen. Jeff Monroe, argued it's a matter of balance and critical inquiry. He said he heard from educators seeking more latitude because they feel pressured under state standards to teach primarily one view on scientific theories such as climate change. He said none would publicly speak about their feelings or testify when lawmakers considered the measure because they feared backlash in their schools and communities.
"All I want is for them to be able to show the strengths and weaknesses of the theory, whatever they're talking about," and for state law to outline that allowance, Monroe said.
Joe Skahan, a science teacher in Lynn, Massachusetts, said he feels strongly about climate change as a problem and ways to address it, but he lets students draw their own conclusions based on what's observable. He devotes several weeks of lessons to climate science and might have students build windmills to learn about renewable energy, discuss rising sea levels or evaluate benefits of energy-efficient lightbulbs.
"It's up to teachers to be confident and, you know, not afraid to keep strong to teach the science regardless of what they're saying at the White House," Skahan said.
Trump said he left the Paris climate accord because it was unfair to the country. Education Secretary Betsy DeVos backed Trump's announcement and told reporters then, during a visit to a charter school in Washington on June 2, that she believes the climate is changing, but she wouldn't answer a reporter's question about whether human activity is causing that.
The Republican president previously downplayed evidence of human impact in climate change and once suggested global warming is an economically motivated "hoax" by the Chinese, though his current beliefs are less clear.
"The president believes that the climate is always changing — sometimes for the better and sometimes for the worse. Pollutants are part of that equation," the White House said in a statement this month.
Evans, of the teachers association, said he doesn't want students caught in political rhetoric but believes Trump is sending the wrong message about climate change and "the value of science in public life."
Students should be presented with evidence, not opinion, and understand topics like climate change by learning the science behind them, not merely accepting others' conclusions, he said.
© 2018 Associated Press