The Environment Report writes:

There's evidence that the Earth is changing because of global warming. Glaciers are receding. Polar ice caps are melting. Weather patterns are altered. That's prompted some people to look for ways to reduce their personal contribution to global warming. Rebecca Williams reports there are many new companies that claim to help you do that... for a price:

Whenever you drive, fly, or ride, you're emitting carbon dioxide. And it's not just the way you get around. It's also any time you turn on lights or plug into an electrical outlet. More than half of the electricity in the U.S. comes from power plants that burn coal and that's another major source of carbon dioxide.

According to Clean Air-Cool Planet, the average CO₂e emissions per year are:

• 4.5 tons for the average U.S. car
  
• 4.5 tons for the average global citizen
  
• 6.2 tons for electricity use of the average U.S. household
  
• 21 tons for the average U.S. resident

and the list goes on. The report also includes CO₂e offsets like moving drivers from SUV's to hybrid cars, replacing aging refrigerators with more energy-efficient models, replacing 100-watt incandescent lights bulbs with 18-watt compact fluorescent bulbs, planting an acre of Douglas Fir trees, and more. The GLRC reports that:

About three dozen companies and nonprofits have sprung up in the past few years. They're selling carbon offsets.

The idea of a carbon offset is to balance out the carbon dioxide that you emit. In theory, you can do this by investing in something like tree planting or energy projects that don't emit greenhouse gasses, such as wind or solar power.

Read or listen to THE PRICE OF GLOBAL WARMING by GLRC Environment Report
Be sure to read the attached A consumer's guide to carbon offsets from Clean Air-Cool Planet (pdf)
Read Carbon Offset at Wikipedia
Visit carbonfund.org, toward a zero carbon world
Visit SELF (Solar Electric Light Fund), Powering a Brighter 21st Century