D. Topics in Computer Science · Topics in Computer Science: Sustainability, Emerging Research and CareersThe Environmental Cost of Computing: E-Waste, Energy and Paper
D1.1About 70 minutes
Learning goals- I can describe the life cycle of a computing device and the resources each stage uses.
- I can explain what e-waste is and why it is a problem.
- I can calculate the energy a device uses with energy = power × time, in watt-hours and kilowatt-hours.
- I can explain how data centres and unnecessary printing add to the environmental cost of computing.
Words to know
e-waste
Electronic waste: discarded devices with a plug or battery, such as phones, laptops, monitors, printers and chargers.
life cycle
All the stages of a product's life: raw materials, manufacturing, shipping, use and end of life.
hazardous substance
A material that can harm people or the environment if it escapes, such as lead, mercury or cadmium.
watt (W)
A unit of power: how fast a device uses energy.
kilowatt-hour (kWh)
A unit of energy: 1000 watts used for one hour. Electricity bills charge per kWh.
standby power
Electricity a device uses while it is switched off or asleep but still plugged in. Also called phantom power.
data centre
A building full of servers that store data and run online services such as streaming, cloud storage and AI.
Your phone has a past
The phone or laptop in front of you started as rock in a mine. Metals such as copper, gold, tin and cobalt were dug up, refined, shipped across oceans and built into chips and batteries in factories that use a lot of energy and water. Then the device was shipped again, to a store and to you. It uses electricity every day. One day it will stop working, or you will want a new one, and it has to go somewhere.
This strand of the course, Topics in Computer Science, starts with the effect computers have on the planet and on people. In this lesson we look at the environment. In the next lesson we look at health.
Where this fits
In the unit Computer Environments and Systems you learn what is inside a computer (processor, memory, storage, power supply). Here we ask a different question: what does it cost the planet to make, run and throw away those parts?
The life cycle of a device
Engineers who study the environment look at a product's whole life cycle:
- Raw materials. Mining metals and making plastics from oil. Mining disturbs land and water and uses fuel.
- Manufacturing. Making chips, screens and batteries takes large amounts of electricity, water and chemicals.
- Use. The device uses electricity for its whole working life. So do the servers it connects to.
- End of life. The device is reused, recycled, stored in a drawer, or thrown out.
Shipping happens between every stage, and shipping burns fuel. The longer we use each device, the more its manufacturing cost is spread out.
E-waste
E-waste is anything with a plug or a battery that has been thrown away. It is one of the fastest-growing kinds of waste in the world. The United Nations Global E-waste Monitor 2024 reported that:
- about 62 million tonnes of e-waste was produced in 2022;
- only 22.3% of it was documented as properly collected and recycled;
- the e-waste of 2022 contained metals worth about US$91 billion, much of it lost.
Why is e-waste a problem?
- Hazardous substances. Electronics can contain lead (in solder and in the glass of old tube-style monitors), mercury (in some older screen backlights), cadmium (in some older batteries) and brominated flame retardants in plastics. In a landfill, or when devices are burned or broken apart without protection, these can leak into soil, water and air.
- Lost resources. Every metal that is not recovered must be mined again.
- Lithium-ion batteries in phones and laptops can start fires in garbage trucks and waste facilities if they are crushed. That is why they must never go in the regular garbage.
Power consumption
Computers use electricity while they are on, and many still use a little while they are "off" (this is standby power). The key formula is:
energy = power × time
- Power is measured in watts (W).
- If time is in hours, energy is in watt-hours (Wh).
- Divide by 1000 to get kilowatt-hours (kWh), the unit on an electricity bill.
A 60 W desktop running for 10 hours uses 60 × 10 = 600 Wh = 0.6 kWh.
The electricity also has an environmental cost. How big depends on where it comes from. Ontario's electricity comes mostly from nuclear and hydro power, which produce little carbon dioxide when they run, but every kWh still needs power plants, transmission lines and fuel or water.
Worked exampleExample 1: A computer left on all the time
A desktop uses 60 W when on and 2 W in sleep mode. Its owner uses it 6 hours a day. How much energy is saved in one year (365 days) by letting it sleep the other 18 hours, instead of leaving it on 24 hours a day? At an example price of $0.13 per kWh, what is the money saved?
- Always on: 60 W × 24 h × 365 days = 525 600 Wh = 525.6 kWh.
- With sleep: each day is 60 W × 6 h + 2 W × 18 h = 360 + 36 = 396 Wh. For a year: 396 × 365 = 144 540 Wh ≈ 144.5 kWh.
- Saved: 525.6 − 144.54 = 381.06 ≈ 381.1 kWh a year.
- Money: 381.06 × $0.13 ≈ $49.54 a year, for one computer.
- Now multiply by a school lab of 30 computers: about 30 × 381 ≈ 11 400 kWh a year. Small habits add up.
About 381 kWh and about $49.54 a year for one computer.
Let Python do the arithmetic
You already know enough Python from Programming Basics to model this. Changing one variable (for example hours_used) lets you test different habits instantly.
on_watts = 60
sleep_watts = 2
hours_used = 6
days = 365
always_on = on_watts * 24 * days / 1000
with_sleep = (on_watts * hours_used + sleep_watts * (24 - hours_used)) * days / 1000
saved = always_on - with_sleep
print("Always on:", round(always_on, 1), "kWh")
print("With sleep:", round(with_sleep, 1), "kWh")
print("Saved:", round(saved, 1), "kWh")
print("At $0.13/kWh that is $" + format(saved * 0.13, ".2f"))
The example numbers (60 W, 2 W, $0.13 per kWh) are made up to show the method. Your own computer's label and your electricity bill give real values. Output (one line each): Always on: 525.6 kWh / With sleep: 144.5 kWh / Saved: 381.1 kWh / At $0.13/kWh that is $49.54
Data centres and the cloud
When you stream a video, store photos "in the cloud" or ask an AI chatbot a question, the work happens on servers in a data centre. Data centres need electricity to run the servers and more electricity to cool them, and many also use water for cooling.
The International Energy Agency (IEA) estimated that data centres used about 415 TWh of electricity in 2024 (1 TWh = 1 billion kWh). That was about 1.5% of all the electricity used in the world. The IEA projected this could more than double to about 945 TWh by 2030, largely because of artificial intelligence.
Paper
Computers were supposed to create the "paperless office", but they also made printing easy. Printing files and emails that never needed to be printed wastes paper, ink or toner (and the cartridges they come in), and the energy used to make all of these. Printing the same file twice to fix one typo doubles that waste.
| Effect | Where it comes from | Example |
|---|
| E-waste | End of life | A drawer of old phones; a monitor left at the curb |
| Hazardous substances | Manufacturing and end of life | Lead in old monitor glass; mercury in old backlights |
| Power use | Use (devices and data centres) | A lab left on all weekend; streaming in high definition |
| Resource use | Raw materials and manufacturing | Mining metals; water used to make chips |
| Paper and cartridges | Use | Printing a 40-page email thread to read once |
Just for funWhy did the old laptop refuse to go to the landfill?
It still had too many good memories. (Wipe them first, then recycle it.)
Hands-on activityHome energy detective
You need: paper and pencil, and the labels on your household electronics. A calculator or Python helps.
- With a grown-up's permission, walk through your home and list every device that is plugged in right now: TV, game console, router, chargers, computer, printer, smart speaker.
- For each device, find the power rating in watts on its label, power adapter or manual (look, don't open anything; never touch the prongs of a plug). If you only find volts and amps, watts ≈ volts × amps. This is the maximum; real use is often lower.
- Estimate how many hours a day each one is on and how many it sits on standby.
- Use energy = power × time to estimate the daily energy of the three biggest users. Write a short Python program like the one above to do the arithmetic.
- Write two habits your household could change (for example a power bar that turns the TV area fully off at night) and estimate the yearly saving.
What to look for: a list of at least six devices, correct use of watts × hours ÷ 1000 = kWh, and realistic suggestions.
Your turn
1Name the four stages of a device's life cycle.
Raw materials, manufacturing, use and end of life (with shipping between stages).
2What is e-waste? Give three examples.
Discarded electronic devices (anything with a plug or battery). Examples: an old phone, a broken printer, a tangle of old chargers.
3Name two hazardous substances that can be found in electronics.
Any two of: lead, mercury, cadmium, brominated flame retardants.
4A 40 W monitor is on for 5 hours. How much energy does it use, in Wh and in kWh?
40 × 5 = 200 Wh = 0.2 kWh.
5Why must lithium-ion batteries never go in the household garbage?
They can catch fire if crushed in a garbage truck or waste facility, and their materials should be recovered.
6According to the IEA, about what share of the world's electricity did data centres use in 2024?
About 1.5% (about 415 TWh).
7Give one way unnecessary printing harms the environment.
It wastes paper, ink or toner, cartridges and the energy used to make them.
More practice: warm-up
1What unit is shown on an electricity bill?
2How many Wh are in 1 kWh?
Power a device uses while it is off or asleep but still plugged in.
4True or false: e-waste only means old computers.
False. It includes phones, TVs, printers, chargers, game consoles and anything else with a plug or battery.
5What two things do data centres use electricity for?
Running the servers and cooling them.
More practice: on your own
1A game console uses 150 W while playing and 10 W on standby. It is played 3 hours a day and on standby the rest. Find the energy used in one day in kWh.
Playing: 150 × 3 = 450 Wh. Standby: 10 × 21 = 210 Wh. Total 660 Wh = 0.66 kWh a day.
2Using your answer above, find the energy for a 365-day year, and the cost at $0.13 per kWh.
0.66 × 365 = 240.9 kWh; 240.9 × 0.13 ≈ $31.32.
362 million tonnes of e-waste were produced in 2022 and 22.3% was documented as recycled. About how many tonnes were not documented as recycled?
62 × 0.777 ≈ 48.2 million tonnes.
4Explain why keeping a phone for four years instead of two is better for the environment, even if the new phone uses a little less power.
Most of a phone's environmental cost comes from mining and manufacturing. Keeping it longer spreads that cost over more years and means fewer phones are made and thrown out.
5Ontario's electricity comes mostly from low-carbon sources. Does that mean leaving computers on is harmless here? Explain.
No. It still uses power plants, transmission and resources, costs money, and adds to demand at busy times. Low-carbon is not zero impact.
Challenge
1A school has 4 labs of 30 computers. Each computer uses 60 W when left on and 2 W asleep. The computers are left on for 16 hours each night, 190 school nights a year. How much energy would be saved each year by making them sleep at night instead?
Saving per computer per hour: 60 − 2 = 58 W. Total: 120 computers × 58 W × 16 h × 190 nights = 21 158 400 Wh ≈ 21 158 kWh a year.
2The IEA projected data centre use to grow from about 415 TWh in 2024 to about 945 TWh in 2030. By what factor is that, and what is the average yearly percentage growth? (Hint: 945/415 = (1 + r)⁶.)
Factor: 945 ÷ 415 ≈ 2.28. (1 + r)⁶ = 2.277, so 1 + r = 2.277^(1/6) ≈ 1.147, about 14.7% per year.
3Write a Python program that asks for a device's watts and hours per day and prints the yearly energy in kWh rounded to one decimal place. Test it with 60 W and 6 hours.
Example: watts = float(input("Watts: ")), hours = float(input("Hours per day: ")), print(round(watts * hours * 365 / 1000, 1), "kWh"). With 60 and 6 it prints 131.4 kWh.
Quiz
1. Which stage of a smartphone's life cycle includes mining cobalt and copper?
2. A 100 W computer runs for 8 hours. How much energy does it use?
3. Which statement about e-waste in 2022 matches the UN Global E-waste Monitor 2024?
4. Why are crushed lithium-ion batteries a danger at waste facilities?
6. Which is an example of a hazardous substance that can be found in old electronics?
Big idea: Expectation D1.1 asks students to explain the negative effects of computers on the environment, such as e-waste, unnecessary printing and heavy power consumption. (Health effects are in the next lesson.)
How to help: Do the home energy activity together. Read the power labels with your teen and talk about which devices could be fully switched off at night. If you have a drawer of old phones and chargers, this is a good time to plan where they will go (Lesson: Where Old Computers Go).
Common difficulties:
- Mixing up power (W) and energy (Wh or kWh). Power is a rate; energy is power × time.
- Forgetting to divide by 1000 to change Wh to kWh.
- Thinking low-carbon electricity means no impact at all.
- Thinking e-waste is only computers. Anything with a plug or battery counts.