Now, more than ever, scientists are saying that global warming is one of the biggest threats to the world's future.
They're calling greenhouse gases from factories, cars and construction a major cause of climate change.
"The construction and maintenance of our buildings, including homes, uses 40 percent of the world's energy and resources, and creates 33 percent or more of greenhouse gases," said Matt Peterson, CEO of the environmental action group Global Green.
Homes are some of the biggest offenders in terms of energy waste and greenhouse emissions.
"We are wasting so much energy, and if we could just corral that, it would be a significant step towards controlling global warming," said environmental activist Laurie David.
John and Susan Zinner are heeding David's advice, running their Santa Monica, Calif., home in an energy-efficient way. By following their example, every American can make their home more green -- and save some greenbacks in the process.
Despite the California sun, temperatures in the Santa Monica region can swing wildly. Balmy, 70-degree weather can change to a brisk 40 degrees in a matter of hours, and heating/cooling costs can add up.
To slash their energy bill and help the environment, the Zinners made some simple changes to their 70-year-old home, making it a model of green efficiency.
The innovation starts in the Zinners' front yard.
"Instead of water-thirsty grass, we've got native plants and a very efficient irrigation system," John Zinner said.
The small amount of water the Zinners provide for the lawn comes from a drip irrigation system that uses far less water than a spray. The system is run by a "smart" sprinkler control.
"It is connected to a satellite, so if it rained yesterday, sprinklers don't go on today," he said. "Secondly, you program it to your plants instead of just saying 10 minutes to that zone. Type in 'shade,' 'plants,' and it automatically figures out how much water it needs."
With no monthly lawn-care fees and minimal irrigation costs, the Zinner family's savings are dramatic.
For the sprinkler controller's one-time $200 price, the Zinners have saved $60 a month in water and lawn maintenance.
A Roof That Makes Money
Energy efficiency continues on the Zinners' roof. When the family moved in, the house was surprisingly hot, because the dark-colored roof was absorbing heat. To cut down on cooling costs, the Zinners painted it with a special, white coating.
"[It's a] dramatic difference," Zinner said. "We stopped using the air conditioner except on really hot days."
The roof coating cost $500 and produced a savings of $30 a month during cooling season.
The roof is also home to solar energy panels that fuel a photovoltaic solar electric system. In California, the sun is so strong, the panels can make more energy than the house needs. The panels actually give money back to the Zinners.
"We are running the meter backwards," he said.
After tax rebates, the panels cost $22,000. Though the investment is substantial, the savings are dramatic. The family's $120 per month electricity bills have been slashed to nearly nothing. The Zinners expect the system will pay for itself in 10 years.
Solar lights are the third energy saver built into the roof. From outside, they look like small skylights. Inside the house, they magnify the sun, delivering strong, natural light, with no power needed.
"This is an interior room, no windows. What makes it work is daylight," Zinner said, showing off a room that looked as if it were lit with traditional lamps.
Each solar light costs $400. Together, they save $20 a month in electricity.
Efficient Windows and Water Heater
Throughout the house, the Zinners installed tall windows and skylights so that during the day, the sun provided all the light necessary. The natural light cuts down on energy costs, but also makes the house more pleasant.
"There's energy savings, but also, it is a more comfortable, livable house when it is full of daylight," he said.
The windows and doors are insulated and dual-paned, with a low e rating for top energy efficiency. Together, they cost $3,000 and save the Zinners $50 per month.
A tankless water heater completes the house's collection of energy-efficient installations. It fits on the wall and warms only as much water as needed, so there's no energy wasted. The tankless heater costs $800 more than a regular heater, but saves $20 each month.
All of the Zinners' appliances are energy star rated. Though they're more of an initial investment, energy star appliances use far less energy than standard ones and save homeowners money in the end.
With a few small changes like those the Zinners made, everyone can make a new home or pre-existing one more green.