— They have a reputation for being environmentally minded do-gooders. But an academic analysis of surveys spanning more than 40 years has found that today’s young Americans are less interested in the environment and in conserving resources — and often less civic-minded overall — than their elders were when they were young.

The findings go against the widespread belief that environmental issues have hit home with today’s young adults, known as Millennials, who have grown up amid climate change discussion and the mantra “reduce, reuse, recycle.” The environment is often listed among top concerns of young voters.

“I was shocked,” said Jean Twenge, a psychology professor at San Diego State University who is one of the study’s authors. “We have the perception that we’re getting through to people. But at least compared to previous eras, we’re not.”

This study, published online this month in the Journal of Personality and Social Psychology, looked at the life goals, concern for others and civic orientation of three young generations — baby boomers, Generation X and Millennials.

Based on two long-standing national surveys of high school seniors and college freshmen, Twenge and her colleagues found a decline over the past four decades in young people’s trust in others, their interest in government and the time they said they spent thinking about social problems.

A recycled plastic water bottle is seen bailed up with other plastic bottles inside the Recology recycling facility in San Francisco, Calif. (Justin Sullivan/Getty Images)

Steepest of all was a steady decline in concern about the environment and in taking personal action to save it.

Researchers found that, when surveyed decades ago, about a third of young baby boomers said it was important to become personally involved in programs to clean up the environment. In comparison, only about a quarter of young Generation X members — and 21 percent of Millennials — said the same.

Meanwhile, 15 percent of Millennials said they had made no effort to help the environment, compared with 8 percent of young Generation X members and 5 percent of young baby boomers.

Millennials also were the least likely to say they had made an effort to conserve electricity and fuel used to heat their homes.

In the case of heating fuel, 78 percent of young baby boomers and 71 percent of young Generation X members said they cut back, compared with 56 percent of Millennials.

It is important to note that most of the survey data available for Millennials were collected before the country’s most recent recession hit.

Mark Potosnak, an environmental science professor at DePaul University in Chicago, has noticed an increase in skepticism — or confusion — about climate change among his students as the national debate has heightened. That leads to fatigue, he said.

“It’s not so much that they don’t think it’s important. They’re just worn out,” Potosnak said. “It’s like poverty in a foreign country. You see the picture so many times, you become inured to it.”

A lot of young people also simply don’t spend that much time exploring nature, said Beth Christensen, a professor who heads the environmental studies department at Adelphi University on Long Island in New York.

Some of her students volunteer with a group that cleans up trash in the bays that surround the island — one of many examples of young people who are taking environmental issues seriously.

At Babson College in Massachusetts, for instance, there is student housing called the “Green Tower,” where residents focus on conserving resources. It is a growing housing trend on many college campuses.

At Muhlenberg College in Pennsylvania students are running a biodiesel plant on campus and building “permaculture,” or indefinitely sustainable, gardens in their back yards.

They are less likely to write a letter to their member of Congress or to try to change things on a global level, said Richard Niesenbaum, a biology professor at Muhlenberg. They also don’t like to label themselves as “environmentalists.”

“In a lot of ways, they’re more pragmatic,” he said.

The analysis was based on two long-term surveys of the nation’s youth. The first, the University of Michigan’s Monitoring the Future project, is an annual survey of thousands of high school seniors, from which data from 1976 through 2008 were used.

Other data came from the American Freshman project, another large annual national survey, administered by the Higher Education Research Institute. Those responses came from thousands of first-year college students, from the years 1966 through 2009. Because of the large sample sizes, the margin of error was less than plus or minus half a percentage point.