Cloud Computing is getting popular day by day as it reduces the cost of business, provides improved services and security. In simple terms, Cloud computing is the delivery of services via the internet, including servers, storage, databases, and much more. It gives the user power to access anything and anywhere through the internet and you typically have to pay only for the cloud services you use. Green Computing is a recent trend towards operating computer systems to be energy efficient and to reduce carbon footprints and E-waste. Cloud computing is reshaping modern networking with a capacity of environmental protection prospects as well. In This paper will talk about the attainments of green cloud computing and green data centers and why we need them. Then, recent studies with some existing work are briefed and environmental issues are explicitly addressed.