The world's future depends on affordable and abundant energy, according to Joseph A. Tainter, a Utah State University professor quoted in the new Leonardo DiCaprio documentary, "The 11th Hour."

The title of the film refers to the conviction that Earth is running out of options and that humans can save the world by making important changes. Produced and narrated by DiCaprio, the movie is to open in Salt Lake City at the end of this month.

Tainter, professor and head of the Logan university's Department of Environment and Society, is the author of the book, "The Collapse of Complex Societies," published in 1990 by Cambridge University Press. His interviews appear in three parts of the film.

The movie isn't only about global warming; that subject occupies about seven minutes of the film's 90. The rest is about human well-being and the way it depends on all sorts of environmental factors, from acid rain to air pollution, from chemicals flowing into the oceans to the disappearance of forests.

As an anthropologist and archaeologist, Tainter has been interested in discovering why former civilizations have collapsed.

The world could be heading toward a situation where "we need more energy to solve our problems and yet we're not able to obtain it," Tainter said in a telephone interview.

Carbon fuels are finite, and their growing scarcity is shown by factors such as the skyrocketing price of gas. "Oil companies are having a hard time producing more; oil exporting nations are having a hard time producing more," he said.

Planners will need to take a serious look at renewable energy sources, he added. Most forms of renewables are based directly or indirectly on the sun: solar energy, wind energy, tidal energy.

That's not to say developing other sources of power will be a panacea. New sources "will have environmental consequences that we need to talk about as a society."

What sort of consequences could be associated with developing wind energy, for example?

"Simply having to take large areas of land and convert them over to wind energy production" could pose an aesthetics problem for some people. Also, "a lot of new transmission lines will need to be put into place.

"But at the same time, something like wind energy gives us a lot of opportunities." For examples, farmers in the windy high plains could instal wind-power generators amid more traditional crops. "There are always trade-offs," he said.

Investors and utilities are starting to see that wind farms could be a good idea, Tainter added.

What's his take on nuclear energy?

Tainter said he is among those who have not given up on nuclear power. "We pretty much dropped nuclear as a serious option after the Three Mile Island incident, and I believe that was a mistake."