Educators unveiled new guidelines Tuesday that call for sweeping changes in the way science is taught in the United States — including, for the first time, a recommendation that climate change be taught as early as middle school.

The guidelines also take a firm stand that children must learn about evolution, the central organizing idea in the biological sciences for more than a century, but one that still provokes a backlash among some religious conservatives.

The guidelines, known as the Next Generation Science Standards, are the first broad national recommendations for science instruction since 1996. They were developed by a consortium of 26 state governments, including Minnesota, and several groups representing scientists and teachers.

States are not required to adopt them, but 26 states have committed to seriously considering the guidelines. They include Arizona, Arkansas, California, Iowa, Kansas and New York. Other states could also adopt them.

Educators involved in drawing them up said the guidelines were intended to combat widespread scientific ignorance, to standardize teaching among states, and to raise the number of high school graduates who choose scientific and technical majors in college, critical for the U.S. economic future.

The focus would be helping students become more intelligent science consumers by learning how scientific work is done: how ideas are developed and tested, what counts as strong or weak evidence, and how insights from many disciplines fit together into a coherent picture of the world.

Leaders of the effort said that teachers may well wind up covering fewer subjects but digging more deeply into the ones they do cover.

In some cases, traditional classes like biology and chemistry may disappear entirely from high schools, replaced by courses that use a case-study method to teach science in a more holistic way.

In many respects, the standards are meant to do for science what a separate set of guidelines known as the Common Core is supposed to do for English and mathematics: impose and raise standards, with a focus on critical thinking and primary investigation.

To date, 45 states and Washington have adopted the Common Core standards.

"This is a huge deal," said David L. Evans, the executive director of the National Science Teachers Association. "We depend on science in so many aspects of our lives. There's a strong feeling that we need to help people understand the nature of science itself, as an intellectual pursuit."

The climate and evolution standards are just two aspects of a set of guidelines containing hundreds of new ideas on how to teach science.

But they have already drawn hostile commentary from conservative groups critical of mainstream scientific thinking.

For instance, as the standards were being drafted, a group called Citizens for Objective Public Education, which lists officers in Florida and Kansas, distributed a nine-page letter attacking them.

The letter warned that the standards ignored evidence against evolution, promoted "secular humanism" and threatened to "take away the right of parents to direct the religious education of their children."

Advocates of climate literacy hailed the new standards, saying they could fill a critical gap in public awareness.

"Quite simply, students have a right to know about climate science and solutions," said Sarah Shanley Hope, the executive director of the Alliance for Climate Education, which offers one-day programs in schools.

Many states are expected to adopt the guidelines over the next year or two, but it could be several years before the guidelines are translated into detailed curriculum documents, teachers are trained in the material and standardized tests are revised.

And all of this has to happen at a time when state education departments and many local schools are under severe financial strain. Inevitably, educators said, some states will do it better than others.

Educators want to introduce students to topics that can be made comprehensible only by drawing on the ideas and methods of many scientific disciplines, one of the reasons that climate change and other large-scale environmental problems are seen as holding so much potential in the classroom.