Claims regarding excessive Greenhouse Gas (GHG) emissions generated by IT technology are growing in number, and some of them leave me scratching my head. As someone who enjoys doing the math to figure out what claims are based in reality and what claims are hyperbolic, I wanted to address one specific sustainability claim about an activity that many of us came to rely on for entertainment during COVID 19: movie streaming.
A joint release by the Federal Environment Ministry and the German Environment Agency is often quoted in the GHG chatter. The release states that the technology used to transmit data from the data center to the user can be as high as a very surprising 90 grams of CO2 per hour.
A digital age Shakespeare might wonder what is more sustainable for the environment and ask, "To download or not to download, and just get in the car and drive to the theater already?"
But my analysis shows that the joint release presents a worst possible case. Going forward, it will be hard to make a case that downloading and watching movies on a smartphone is going to be a major contributor to GHG emissions. In fact, my analysis shows that you can download and watch 3,383 films on your 5G phone for every trip to the theater!
Doing the math to find out what is more sustainable for the environment
Let's take a deeper look:
Storage - Many instances of the movie are distributed (cached) in local data centers, which are located in close proximity to the people who are downloading it, greatly increasing the speed of the download. The CO2 emissions generated in a data center are relatively low, at 1.5 grams of CO2 per hour1. if we assume a conservative 24 downloads per day or one per hour. Algorithms are used to make sure only fresh content is stored locally. However, the storage technology used will also have an effect. Solid state storage (SSD), the most energy efficient, will greatly reduce this 1.5 grams of CO2e per hour worst case to 0.5 grams of CO2e per hour best case (estimate).
Transmission - Transmitting data from the data center to the user can be as high as 90 grams of CO2 per hour. But that's using 3G (which is starting to be decommissioned in many areas). If new 5G is used, only 3.5 grams of CO2 are emitted per hour, and the ubiquitous 4G is 11.5 grams1. Plus, it takes only seconds to download a movie using 5G while it will take tens of minutes with 3G. If we take a worst case 3G download, it's 90g CO2e per hour and say it takes 20 minutes to download, that means it's 30g CO2e per movie for transmission. The best case is 5G with 3.5g CO2e per hour, say a 20-second download equates to 0.0194g CO2e per movie for transmission.
Phone Power Usage - If we assume a five-watt (W) charger to fully charge a phone one hour each day, this calculates to 5 Wh per day and a total of 1.825 kilowatt-hours (kWh) of electricity per year to charge your phone.2
The CO2 emissions vary by geographic area, with the low in South America 0.35 kgCO2e and the high in Africa with 1.69 kg CO2e per year by charging one phone each day. If we say the average is 0.75kg (750g) CO2e per year, the average per day is 0.002kg, or 2g CO2e per day. Watching a two-hour movie uses roughly 25% of the phone's charged battery capacity, we get 0.0005 kg or 0.5g CO2e to charge the phone back up after each movie.
Summary - the equation to download and watch a movie on a smartphone is: Transmission + Data Center Storage + Phone Power Usage = CO2e per movie.
Worst Case: 30+1.5+0.5= 32.0g CO2e per movie
Best Case: 0.194+0.5+0.5 = 1.194g CO2e per movie
The result: download and watch 3,383 films on your 5G phone for every trip to the theater.
Download or drive for sustainability?
When we compare downloading versus attending a movie in a theater, transportation to get there along with heating and cooling the theater needs to be factored into the GHG equation. (Of course, there are other considerations like embedded carbon to manufacture the phone that are not considered here). If we make the assumption that heating and cooling a home is around the same energy use as the average heating and cooling per person in a theater, we are left with transportation to the theater. The average gas burning passenger vehicle emits about 404 grams of CO2 per mile3. If we assume the movie theater is five miles away, a round trip is 4,040g CO2e per movie.
Sure, electric vehicles cut down on GHG, but right now the majority of electricity used to charge their batteries is being generated by burning fossil fuels and there are additional losses in transmission. For example, if I look at a full BEV (battery electric vehicle) in the United States, the average GHG is around 210 grams of CO2 per mile3. This is highly dependent on your location and will decrease as more renewable generation comes online. When compared with worst case 32.0g CO2e and best case 1.194g per movie downloaded and watched on your smartphone.
It always helps to put these numbers into perspective, so let's use the average annual household electricity consumption in 2020; 10,715 kWh5 and the CO2e for North and Central America tells us that the average electricity use of a U.S. home produces 3,687kg CO2e per year or 3,687,000g CO2e per year. With worst case: 32.0g CO2e per movie and best case: 1.194g CO2e per movie, it's clear that movie downloads will be fairly insignificant. Even the worst case is only 0.001% of a household's yearly GHG emissions or 0.32% of a household's daily GHG emissions to download and watch one movie.
So, the next time you hear some of the growing chatter about sustainability and movie downloads causing significant GHG emissions, you have some math to reference and debate which claim is grounded in reality and worthy of your concern.