By Deborah Zabarenko

(Reuters) - A new Tennessee law protects teachers who explore the "scientific strengths and scientific weaknesses" of evolution and climate change, a move science education advocates say could make it easier for creationism and global warming denial to enter U.S. classrooms.

The measure, which became law Tuesday, made Tennessee the second state, after Louisiana, to enable teachers to more easily teach alternative theories to the widely accepted scientific concepts of evolution and human-caused climate change. At least five other states considered similar legislation this year.

The heart of the law is protection for teachers who "help students understand, analyze, critique, and review in an objective manner the scientific strengths and scientific weaknesses of existing scientific theories covered in the course being taught."

Science education advocates say this leaves latitude for teachers to bring in material on creationism or climate change denial, which they consider unsound science.

The law was billed as a triumph of academic freedom by proponents of creationism or intelligent design, who reject the concept that human beings and other life forms evolved through random mutation and natural selection.

The Tennessee measure "protects teachers when they promote critical thinking and objective discussion about controversial science issues such as biological evolution, climate change and human cloning," said a statement from the Seattle-based Discovery Institute, which promotes intelligent design.

But Brenda Ekwurzel of the Union of Concerned Scientists saw a risk to education: "We need to keep kids' curiosity about science alive and not limit their ability to understand the world around them by exposing them to misinformation."

Tennessee's action came 87 years after the 1925 "monkey trial" in which John Thomas Scopes was tried for teaching evolution in Tennessee.

The state legislature overwhelmingly approved it, and Governor Bill Haslam let it become law without his signature, tacitly acknowledging that a veto would not be sustained.

In a statement, Haslam said the legislation did not change the state's scientific standards or school curriculum, or do anything unacceptable in Tennessee schools.

On such controversial subjects as "biological evolution, the chemical origins of life, global warming and human cloning," the law stipulates that teachers cannot be barred from helping students understand "the scientific strengths and scientific weaknesses of existing scientific theories."

The law protects the teaching of scientific information, not religious or non-religious doctrine, which is important, since that could stray into unconstitutional territory. But science educators worry that teachers could offer unsound science, or non-science, and be protected by this legislation.

CREATIONISM IN THE CLASSROOM

Josh Rosenau of the National Center for Science Education said the law could easily come between administrators and teachers, if science teachers bring creationist or climate change denial ideas into their classes.

The U.S. Supreme Court ruled in 1987 that requiring that creation science be taught in public schools alongside evolution is unconstitutional as a violation of the First Amendment right to freedom of religion.

The Tennessee law might make it harder for administrators to prevent the introduction of creationism in the classroom, Rosenau said by telephone. And any legal challenge by parents or others would be "tricky," he said.

He cited a survey of U.S. high school biology teachers published in the journal Science in 2011 that found about 13 percent of those surveyed "explicitly advocate creationism or intelligent design by spending at least one hour of class time presenting it in a positive light."

The survey found only about 28 percent consistently followed National Research Council recommendations for introducing evidence that evolution occurred.

The rest, about 60 percent, avoided controversy by limiting evolution instruction to molecular biology, telling students they need not believe in evolution to score well on tests, or exposing students to all positions, scientific and otherwise, to let them make up their own minds, the article said. ( https://www.sciencedaily.com/releases/2011/01/110127141657.htm )

In teaching climate change, Ekwurzel said the U.S. National Academy of Sciences offered useful classroom information in a May 2010 report that affirmed the reality of climate change, its largely human cause and the significant risk posed to human and natural systems.

But James Taylor of the Chicago-based free-market Heartland Institute, which plans to offer a global warming K-12 curriculum pointing up scientific disagreement about the impact of climate change, questioned the academy's assessment and those who advocate it.

"To gloss that disagreement over, to pretend that it does not exist, is misrepresenting the science and doing a disservice to students and teachers alike," Taylor said by phone.

(Reporting By Deborah Zabarenko; Editing by Marilyn W. Thompson and Cynthia Osterman)