The other cost

You probably know that airfares are shooting up right now, thanks to the crazy cost of fuel. Some airlines are nickel-and-diming passengers with fees for checking bags, sitting in certain seats, and even having a soda in-flight.

But do you know the cost of that flight in CO2 emissions? That's what programmer and environmentalist Michael Mandiberg calls the "real costs" of travel.

He's plugged flight origination and destination information from airfare websites like Orbitz.com into a little widget called Real Costs that you can download and install into your Firefox web browser.

Then when you surf for airfares on supported websites, you'll see an orange overlay that states the pounds of CO2 your chosen flight would generate. The Real Costs plug-in compares the flying emissions with cars, buses, and trains, plus it offers links to carbon-offset companies.

Add the CO2 costs to the financial sticker shock of airfares today, and you might think twice about those discretionary trips. At some point, Real Costs will be available for car travel too.

Get an insider's perspective from Real Costs founder Mandiberg with this interview on Yahoo! Video.