Due to demand for computer resource cloud based centers are expanding. Exponential growth of data centers has increased energy consumptions to an alarming rates. Impact on environment is proportional to high energy utilization in form of Carbon-dioxide emissions. To maximize various IT resources, cloud computing has produced an ultimate and interesting way to virtualize server and data centers to make it energy efficient .Green cloud computing refers to eco-friendly usage of computers and resource with respect to IT industry. It involves designing, calculating and usage of computing devices in such a way that it can lower any adverse impact on environment.
The availability of high capacity network, low-cost computers and storage devices as well as the widespread adoption of service oriented architecture, hardware vitalization, autonomic and utility computing has promoted growth in cloud computing. Without cloud computing ,from 1-1.5% of worlds total power is consumed by data centers . It is possible for data centers to run more efficiently by cloud computing .
Annual energy saved between 2015 to 2020 could amount to over $12 billion with help of cloud computing in larger companies.This is the study conducted by the Carbon Disclosure Porject(CDP). Today google has achieved 50% decrease in data center ower consumption by cloud computing which proves energy efficiency .
The eminent obstacle faced by mankind is exhaustion of fossil and fuels to support civilzation. Emission of green-house gas by excess energy consumption is the major factor contributing to current global warming. It is essential for mankinf to push towards green technology.
As internet has been part of our life ,cloud computing has emerged as new kind of “utility” that gets delivered through wired or wireless networks. Network based services both to cooperate and individual end users through high speed internet and cooperate IP connections is called “Cloud Computing Service”.\nGreen cloud computing uses the strategies and the development of computer system that look to utilize resource efficiently in order to decrease the impact of IT process on environment . This can be achieved either Product Logetivity Resource Allocation or Virtualization or Power Management .
Reviewing literature plays a key role in creating a reliable foundation of advancing knowledge, according to Webster and Watson. Both academic and non-academic literature are surveyed in order to obtain a sense of current state of green cloud computing studies. Initially we combined sources from conference papers, journal papers, technical reports, books from multiple scientific database ISI Web of Science Association for Computing Machinery (ACM) Digital Library , IEEE Computer Science ,Scopus and Science Direct . These journal helps to gain access to leading computer science journals and high–quality peer reviewed computer science conference publications. The keywords used were “green cloud computing”, sustainable” and “sustainable cloud computing”.
The concept of green cloud computing had attracted the attention of researchers at 2009. Reports published directly by ICT organizations, NGO’s and other sources for non-academic studies were analyzed. Studies and opinions obtained from the sources influence the attitude towards green cloud computing for wide variety of users. Academic and non-academic research complement each other. The study of both sources offers a complete picture of Green cloud computing, which is very important technically and socially.
Evolution of cloud computing:
Cloud computing is an access provider of computing service to computer user. Companies pays a fee based on consuming time and resource used . Cloud computing helps a company to enlarge its network and server infrastructure. Network and server capacity is added automatically to a company’s website by cloud computing service as the demand for service of website increases. A server and network capacity maybe be replicated around the world so that, for example, a single outage of sever does not affect the company’s operations. Many sever and personal computer combined on network such as internet to act as one large computer is referred to as Grid computing. Grid computing is commonly used for research environment such as climate research and life science problems. Technology which is responsible for environmental change is Green Cloud Computing. 17 inch monitor that are always turned on release 750 pounds of carbon in one year which is equivalent to carbon dioxide released by car driven 820 miles. Conserving computers electricity consumption is done along with maintaining acceptable performance by power management software. The software checks when a computer is inactive and shuts down the computer. The main focus is to perform computations with as few Joules as possible, by re-routing the computations to a more efficient destination etc.
The attention received by green computing from the computing community led to the rise in interest in studying the influence of cloud computing .It was a reaction to the report published by Gartner which estimated that the global ICT industry accounted for approximately 2% of global CO2 In 2009, Liu et al presented Green Cloud a new architecture which aims to decrease data center power consumption . The studies on green cloud has been intensified since 2009 and the interest in finding methods to decrease energy consumption is even older. These studies were very essential for green cloud computing evolution. Energy efﬁciency is increased, CO2 emissions and e-waste are decreased in green data centers , not only for ICT equipment, but for all environmental aspects (building, lightning, cooling, etc.)—are the basis for actual and future green cloud computing. Along with energy consumption of computer devices, Green cloud includes the energy consumption of networks or cooling equipment, but also other environmental issues, such as CO2 emissions, (e-)waste management, and consumption of natural resources. In this frame of reference, researchers are analyzing the relationship between “sustainability” and “cloud computing”. The advancement of this research was directed by the increase in interest in the environment and by the extended use of cloud computing. Figure illustrates the growing interest in green cloud computing in the academic literature between 2009 and 2016, with the single exception of 2013.
The technology is beneficial as:
Reasons for green cloud computing being environmental friendly: Virtualization  Virtualization in cloud computing creates virtual platform of server operating systems and storage devices .It helps the user by providing multiple machine at the same time and allows sharing of single physical resource to multiple users. It manages workload by reconstructing traditional computing and make it more scalable, economical and efficient .The main factor for cloud computing is to attain sustainability from cost and energy efficient point of view. There are two types of virtualizations mainly used:
Reducing energy consumption : It helps in preventing overheating by balancing the workload across many server.
Reducing carbon emission : Carbon emission can be reduced as the energy consumption is reduced by load . Cloud enabling green computing Helps in significant improvement in energy efficiency by sharing the same infrastructure .
 Dynamic provision : In traditional computing, datacenter and private infrastructure are used to maint to fulfill worst case demand. Multi-tenancy : Energy and carbon emission can be reduced.
Server utilization : Sometimes on premise infrastructure runs with very low utilization .Using virtualization same application can hosted and used on the same server thus lead to utilization up to 70%.
Datacenter efficiency : By using the most energy efficient technologies ,cloud providers can improve the PUE of datacenter .
The three types of cloud models are:
The applications available for use are with paid licensed subscription which run on vendor’s cloud. SaaS model helps to quickly access cloud-based web applications without committing to install new infrastructure. it eliminates the need to install ,update and maintain applications on each of your computers.
Affordable Hardware is not required for this making it cost effective . Accessible Everywhere Due to internet cloud based application are accessible everywhere . SaaS platform are useful for companies that require frequent collaboration as their employees can access the programs easily. Ready-to-Use With SaaS, the programs you need are already fully developed and ready to use. In comparison with other two platforms the set-up time for SaaS programs is greatly decreased.
Disadvantages of SaaS
Lack of Control If you don’t feel comfortable releasing the control of your applications to another party, it’s not the best option as vendor has control over the program that your company is using. Slower Speeds Depending upon internet access to function, SaaS applications tend to be slower than client/server applications. Variable Functions & Features Features and functions are less in SaaS cloud-based applications than their client/server counterparts. This disadvantage may be invalid if your business only needs the features offered in the SaaS version to function.
Third-party trafficker is hosting the cloud infrastructure that supports the platform. Third-party trafficker provides your business with a platform upon that your business will develop and run applications. PaaS removes your need to install in-house hardware or software package. Your business wouldn't manage the underlying cloud infrastructure, however you'd maintain contorl over the deployed applications.
Advantage of PaaS 
Rapid Time-to-Market PaaS simplifies application management by eliminating the necessity to keep up and manage the underlying infrastructure .As a result ,applications will be developed and deployed quicker. Cost Effective Development A cloud –based platform provides your business with a base upon that to make your applications ,as opposition building from nothing, therefore dramatically reducing the prices associated Scalability Cloud based platforms supply reusable code that makes it easier to develop and deploy applications
Disadvantages of PaaS
Security & Compliance The vendor stores most of applications data in PaaS model. This proves troublesome because the merchant could also be storing their database via 3rd party, therefore harming security of your knowledge . Lack of Compatibility. It is attainable that your current infrastructure might not be compatible with a cloud platform. If some parts cannot be cloud-enabled, you will have to be compelled to switch from your current apps and programs to cloud-compatible counterparts so as to completely integrate. Alternately you will have to be compelled to leave these parts out of cloud and at intervals your current infrastructure.
IaaS , the most versatile of the cloud models permits your business to possess complete ,scalable management over the management and customization of your infrastructure In the IaaS model, the cloud supplier hosts your infrastructure parts that will be present on-site information center(such as server,storage and networking hardware). Your business however, would maintain management over operative systems,storage,deployed aplications and presumably restricted management of selected networking parts(eg. Host firewalls).
Advantages of IaaS
Eliminates Capital Expenses Helps in removing capital expense of deploying in-house hardware and software Additionally ,IaaS usually is obtainable as a pay –as- you-go model, with charges based mostly either in time ,or within the quantity of virtual machine house that was used. Supports Flexibility IaaS is beneficial in supporting workloads that are temporary, could modify unexpectedly, or are experimental. Like all workloads these loads need infrastructure to support them. cloud based infrastructure answers the necessity for flexibility. Simple Deployment It is easier for your cloud supplier to deploy your servers, processing, storage and networking within the IaaS model than to deploy these parts in-house, with no previous no base to build off. As a result, your period can increase as your systems are accessible to be used sooner.
Disadvantages of IaaS
Insight Because your entire infrastructure is maintained and controlled b your IaaS supplier, its rare that you are going to be given the small print of its configuration and performance .In turn ,this could create systems management and observance harder for your company. Variability of Resilience The availability and performance of the workload is very dependent upon the supplier. If the IaaS suppliers experiences internal or external time period,your workloads also will be affected. Costly IaaS models are generally more expensive than Paas and SaaS models as a result they provide more support to your business than the other two cloud models. However, they’ll still be cost-efficient supported their utility to your business.
Today’s IT services are using the cloud computing solutions so as to offer to its clients the required services efficiently. Except that the high use of the cloud engenders a large growth in its data center infrastructure. In this case, unfortunately, an enormous amount of electrical energy is consumed and a high amount of carbon dioxide is emitted in the air. Thus, reducing the energy consumption in cloud data centers while assuring an optimized management of its resources including VMs and servers is becoming a needful aim to achieve. This requirement is related to the green cloud concept by which we can contribute to the environmental protection. In this paper, various techniques for enhancing the green cloud resources allocation are discussed and which are based essentially on virtualization, migration, and consolidation. Thus, the proposed solution provides an optimized resource management while considering all major energy parameters and major possible constraints of VMs allocation in PMs and which influences on the energy consumed in the cloud computing data center. Also, we focused on taking energy performance trade-off in concern.