To Print or Not to Print?

A1:  Computers are discarded before they stop working

A2:  Monitors are discarded before they stop working

A3:  Most documents in homes/offices are printed on a laser printer ((Consumer inkjet printing is more expensive, so those that require high volumes of printing are probably using laser printers.))

A4:  Printers are discarded only when they stop working

A5:  Printer fuser breaks after ~100000 sides

A6:  Printer toner cartridges are used until empty

A7:  Each cartridge lasts for 2000 sides

A8:  Only new cartridges are used; no recycled ones are used

A9:  Fossil fuels required to build a printer are about the same as building computer

A10: Printer weight is 5kg/printer

A11: Printer uses 500W while printing

A12: Only uncoated paper from non-recycled paper is used

A13: There is no proactive tree planting

A14: Computer/monitor consuming 0W when reading paper printout (e.g., reading on the subway)

A15: Printers print at 8 pages per minute

A16: All the CO₂ from paper manufacturing from tree logging to consumer is the same as transporting it 12000km (i.e., we can lump in all the other CO₂ from manufacturing paper by inflating the emissions due to transportation).  This is the same as transporting the paper across the full length of the Trans-Canada Highway 1.5 times.

A17: Printers only use 20 lb copy paper

A18: We can ignore the embodied energy of creating a truck

A19: Employees of factories and power plants generate a net of 0 CO₂; they would produce this CO₂ regardless of where they were employed

A20: Computers used for reading documents/printing would have been purchased, even if they were not used for reading documents/printing

A21: Printers are turned off when not in use ((Standby for laser printers is quite high — in the 10-50W range.))

A22: Printing is always double sided and both sides of the page are used.

A23: No misprints

A24: Computer is running at idle power while viewing documents on a screen

A25: Low power computer uses 80W (based on measurements around the lab in which I work, looking at computers in the lower quartile of consumption — much lower consumptions are possible)

A26: 24″ LCD monitor uses 50W at medium brightness (LCDs with LED backlights use quite a bit less power)

The Upshot

How often does one spend 6 minutes or more reading a page?  Perhaps not that often.  On the other hand, there may be some papers that one reads over and over again or perhaps shares with others that will result in a cumulative reading time of over 6 minutes.  In such situations, printing will result in less CO₂ emitted.  Remember, this comparison only deals with CO₂ and none of the other ickies produced during the paper-making process or computer equipment manufacturing.

Note that in this analysis, I have systematically given reading on a computer an advantage!  If one uses recycled paper and toner, paper’s CO₂ impact drops by about 50% and you get 3 minutes to read a page to reach break-even (remember, these numbers change depending on how clean/dirty your energy source is).  Further, one need not replace an entire printer when only the fuser breaks.  Of course, one could also use a lower power computer.  I’ve measured the power consumption of the laptop I use, a first generation MacBook Air, to be 10W with Wi-fi on and the screen at medium brightness.  That’s 8% of the hypothetical system in the measurements above, allowing me to read 13 times more slowly and spend about 40 minutes reading a page instead of printing on recycled paper with reused toner to break even.  On the other hand, a more power hungry system results in less time to break even.  A dual 24″ monitor setup on a more powerful computer with a high-end graphics card would require reading at a rate of more than 1 page/minute to be more CO₂ efficient than printing out the page.