The CCI grades cities based on their efforts to combat climate change and ranks over 50 city policies that focus on reducing city CO2 emissions. The index presents both a number value for the city's estimated annual greenhouse gas (GHG) emissions (in millions of metric tons of carbon dioxide [CO2]) and a letter grade that reports how well the city is doing to adopt and implement GHG reduction policies. The CCI also strives to build a network of activists by providing action alerts and other resources that encourage citizens to push for political action at the local level and create positive environmental change within their communities.