The California Climate Credit, Explained.

Twice a year, California residents enjoy a credit towards their electricity bill. The a similar credit is applied once a year to residents’ natural gas utility bills. But why?
Natural gas distributers, power plants, and large industries that emit greenhouse gases are required to buy carbon pollution permits in California in an effort to fight climate change. A portion of the sale of these permits gets passed back to you, the consumer, with the intention of providing opportunities for you to take advantage of upgrades that can be made to save energy and money, and that ultimately benefit the environment and fight climate change.
Investor-owned utility companies (PG&E, SDG&E, SCE, Pacific Power, Liberty Utilities, SoCalGas, Southwest Gas) and Community Choice Aggregator (CCA) customers are those that benefit from this credit, since they are under the California Public Utilities Commission (CPUC) purview. The current provisions for the California Climate Credit will last until 2020.
Additional information can be found here.