"An Inconvenient Truth," Al Gore's movie on global warming, is now the fourth-largest-grossing documentary of all time. But apparently it isn't young adults who are paying the price of the ticket — or, more important, taking the truth about the environment to heart. In fact, the inconvenient truth today is that youths' willingness to conserve gas, heat and energy has taken a precipitous plunge since the 1980s.

According to data from Monitoring the Future, a federally funded national survey on trends in the attitudes, values and behavior of high school seniors since 1976, there has been a clear decline in conservation behavior among 18-year-olds over the past 27 years — although we are not yet sure whether these attitudes follow youths into adulthood. This decline, interestingly, is coupled with a rise in materialistic values.

In fact, trends in materialism and conservation are highly related: At times when youths place higher value on material goods, they are also much less likely to say they would conserve resources. And when youths are more materially driven, they are also less likely to believe that natural resources will become scarce in the future.

Since the 1990s, the trends in materialism seem to have topped out at a steady high level, while willingness to conserve keeps declining. These opposing values should raise a red flag about the consumer culture and its influence on youth.

Youths also consistently believe that government is more responsible for the environment than they are personally. Importantly, when they perceive that the government's role in solving environmental problems is declining, so does their belief that they, personally, must do their part to save the environment.

Conservation is a collective responsibility. Likewise, in the minds of youth, their own actions to preserve the environment are inextricably linked to their perception of the government's role in environmental conservation.

Indeed, environmental attitudes of youth seem to mirror the opinions of those in the White House at the time. The highest levels of conservation occurred in the mid- to late 1970s, at the same time President Jimmy Carter was publicly petitioning citizens to take individual responsibility for conserving resources. The steepest decline in conservation occurred during the Reagan administration, which has been widely criticized for its environmental policies. Willingness to conserve enjoyed a slight surge around 1992-93, when Bill Clinton first took office, but this increase was short-lived. (Al Gore must not have been speaking up too loudly about the environment back then.)

The good news in these trends is that when government responds, so do youth. If our country's leaders follow the example of Al Gore and start to genuinely explore sustainable solutions, it's likely that young people will follow suit.

Policymakers and elected officials might also want to note that when youths embrace conservation and pro-environmental attitudes, they are more likely to engage in conventional politics, from writing to officials to giving money to a political campaign, or working on a campaign.

Gore argues that in America, "political will is a renewable resource." Perhaps one way to renew this resource is to start focusing more on young people and their understanding of, as well as contribution to, environmental problems.

Laura Wray is a graduate student and Constance Flanagan a professor of youth civic development at Pennsylvania State University. They work with the MacArthur Research Network on Transitions to Adulthood in mapping the attitudes of young adults. They wrote this commentary for The Washington Post.