Save the thermostat, save the world.

Or something like that. The New York Times David Leonhardt explores the "paradox of thrift"

McKinsey & Company recently analyzed household spending on energy, for example, and found enormous waste. People heat their homes when they are not there and, thanks to leaks in their walls and heating ducts, also heat the airspace above their roof.

A programmable thermostat, which adjusts the temperature when people are out of the house or asleep, can cost as little as $50. For less than $1,000, people can buy the thermostat, as well as hire a contractor to fix leaks and replace their light bulbs with more efficient ones. In either case, the spending often pays for itself in just a year or two.

“There is a difference between consuming and investing,” says Ken Ostrowski of McKinsey. “And energy efficiency falls more into the category of investing.”

So get out there an invest, buy a programmable thermostat. Save the economy, save the world. Another great investment is to invest in services, get a massage or ten instead of buying a flat screen TV. Borrow some board games, and have a fun night out with your friends and family.

The definition of investment is that which returns beyond your outlay. Learn a skill, learn an instrument, read to a kid. The investments are out there, we just have to discover them.