Information technology is growing at an exponential rate and has direct impact over the entire society. Data centers are the building blocks of IT business organizations. Most of the Internet traffic is concentrated on data centers as maximum computation and storage are moving into the cloud that provides the capabilities of centralized repository for storage, management, networking and dissemination of data. These data centers consume tremendous amount of energy. All data center are plagued with thousands of servers as major components. These Servers emits Carbon foot prints thus raising the requirement of more green computing techniques. These techniques require attention for formal energy consumption issues. Current studies basically focus on the existing approaches and challenges for Data center optimization to achieve Green Computing. This paper presents a systematic overview on paper Virtualization, cloud computing and energy efficiency methods as well as drop of carbon emission from data centers.