## 1 Introduction  
There is overwhelming scientific evidence that human activity is the biggest contributor to climate change through greenhouse gas (GHG) emissions. The production and utilization of fossil-based energy sources are the largest contributors to anthropogenic GHG emissions [1]. The Intergovernmental Panel on Climate Change (IPCC) suggested limiting global warming to \(1.5\,^{\circ}\)C above preindustrial levels [2], requiring the development and deployment of cleaner energy technologies. These clean technologies should provide significant GHG reductions with a large potential market capture. Currently, transport, industrial activities, and building are the largest economic sectors driving fossil energy demand. The information and communication technology (ICT) sector is receiving relatively little attention. Recent reports showed that in the worst-case scenario, this sector could become a dominant energy user, potentially consuming as much as half of global electricity in 2030 [3]. Another report indicated that the overall carbon footprint of the ICT sector is expected to increase significantly [4]. The deployment of 5G networks and the prevalence of Internet of Things (IoT) devices will continue to drive the fast growth of energy demand in the ICT sector. Energy demand for IoT devices is expected to increase by a factor of 17 between 2016 and 2025 [4]. This will add additional pressure to current commitments to reduce GHG emissions, particularly if there is no significant reduction in other sectors. Indeed, a growing global economy and increasing energy demand, combined with a lack of cost-competitive, large-scale renewable power generation, has led to increasing emissions [5]. Even with increasing renewable energy, demand for coal and natural gas will continue to grow due to increasing global electricity demand. Improved efficiency at the device level (TV monitors, smartphones,computers, tablets, and modems) has led to reduced unit electricity consumption (J/bit), but overall consumption is increasing due to the growing demand from additional features and services. Electricity demand from different network layers is also expected to increase. For example, electricity demand for Wi-Fi networks is anticipated to grow from today's 250 TWh to 4500 TWh in 2030 [3]. This 20-fold increase in demand within a decade could not be compensated for just by the gain of efficiency. To provide perspective and significance to this challenge, Canada produced 652.3 TWh of electricity in 2017, representing 3% of global electricity production [6]. [PERSON] and [PERSON] [3] developed three case scenarios for overall energy demand from the ICT sector. In these three different scenarios devices, communication networks, and data center consumption are considered. These scenarios include annual numbers of sold devices, data traffic, and electricity intensities. The ICT sector is expected to be responsible for up to 51% of the total world power demand. This could lead to higher consumption of fossil fuels, as this is the only scalable, cost-effective, and ready-to-deploy source of electricity. The deployment of carbon-neutral 5G networks [7] will thus require the development of scalable clean electricity sources that are easy to integrate within telecommunication networks. There are numerous potential software and hardware solutions to address increasing GHG emissions within the ICT sector. Energy consumption per bit transferred through wireless networks has been reduced using new antenna technology known as massive multiple-input multiple-output (MIMO) [8]. The deployment a 5G networks will probably not proceed on a linear basis. For example, standby mode was not built in 4G networks, which leads to energy waste when base stations (BSs) are not all needed during off-peak demand [9]. Thus, it is quite difficult to accurately forecast GHG emissions, as heterogeneous network architectures are expanding, and overall energy demand is increasing.