If you went to the concert you can go to a site that the company has setup at www.esurance.com/sos and enter your mileage. Esurance will buy carbon offsets from NativeEnergy, a company that works with Native American farmers to build renewable energy projects. They then sell the carbon credits based on those installations. Now the question is will anyone offset all the carbon generated to power all the amps and equipment used to setup and put on these concerts all over the world?
[Source: Esurance.com, thanks to Linton for the tip]