It takes energy to get the data to the data center—miles of fiber optic cables, studded with other fixtures of internet infrastructure that all require power along the way.
At the center, your data is stored multiple times on hard disks, and the constant activity of all those disks creates a lot of heat, which necessitates energy-intensive air conditioners to protect the equipment from overheating.
If you save and store 100 gigabytes of data in the cloud during a year, enough space for several thousand photos or a few hours of video, the amount of electricity required to accomplish this would result in the emission of about 0.2 tons of CO2
Source: https://stanfordmag.org/contents/carbon-and-the-cloud
Datacentres set to consume third of Ireland’s energy by 2026.
Source: https://www.computerweekly.com/news/366567892/Datacentres-set-to-consume-third-of-Irelands-energy-by-2026
Cloud Carbon Emissions Measurement and Analysis Tool