Case 1: Comparison of CO2 Emissions from an Environmental Perspective
Comparison of CO2 Emissions Generated When Reading Documents
The following are calculations of CO2 emissions generated when information is read using paper as medium and when read using electronic devices. Using the publicized data on CO2 emissions generated throughout the entire lifecycles of some products on the market, the average values of CO2 emissions throughout the entire lifecycle of computers, displays, and printers released in 2008 or later are calculated. Using each average value, CO2 emissions per unit quantity (CO2 generated by using a device for an hour or outputting one sheet) are then calculated. Because CO2 emissions vary significantly depending on the processor or memory capacity of a computer, we categorize computers into two types: standard computers with memory capacity up to 4 GB, and high-performance computers with memory capacity greater than 4 GB. Displays targeted for setting CO2 emissions per unit quantity are limited to those having a resolution of 1280 x 800 or more, and which are often used in offices (Table 1). CO2 emissions per one sheet of OA paper is considered to be 5 g based on the CO2 emission unit table (2007 version) of the Center for Environmental Information Science.
Table 1: Prerequisites (CO2 emissions per unit quantity)
|CO2 emissions per unit quantity|
|Laptop computer||27.6 g/h|
|Standard computer (17-inch display is used)||72.9 g/h (standard PC: 49.60 g/h + 17-inch display: 23.3 g/h)|
|High-performance computer (19-inch display is used)||124.7 g/h (high-performance computer: 98.42 g/h + 19-inch display: 26.3 g/h)|
|OA paper||5 g/sheet|
Example: Reading an eight-page document
The following compares CO2 emissions when an eight-page document is read for 30 minutes. The four kinds of media—paper, laptop computer, standard computer, and high-performance computer—are compared. When paper is used and an eight-page electronic document is printed on both sides of paper, four sheets are output and CO2 emissions generated are 30.3 g-CO2.Note1 Table 2 lists the CO2 emissions when the document is read for 30 minutes using a laptop computer, a standard computer, and a high-performance computer.
Table 2: Comparison of CO2 emissions when using different media to read the same document
|When reading an eight-page document for 30 minutes|
|Print the document on both sides of paper||4 sheets × (5 g-CO2 + 2.58 g-CO2) = 30.3 g-CO2
number of sheets × (CO2 emissions of paper per sheet + CO2 emissions of printer per sheet)
|Use a laptop computer||27.6 g/h × 0.5 hr. = 13.8 g-CO2|
|Use a standard computer||72.9 g/h × 0.5 hr. = 36.5 g-CO2|
|Use a high-performance computer||124.7 g/h × 0.5 hr. = 62.4 g-CO2|
- Note1 Comparison of CO2 emissions: g-CO2 is the unit for measuring CO2 emissions.
Figure 1 shows the relationship between the amounts of time spent on reading the document and CO2 emissions. In the case of reading a document on paper, CO2 is generated only while the document is being printed, but in the case of using a computer, CO2 emissions increase in proportion to the amount of time spent on reading the document. Compared to when using a laptop computer, reading a document printed on paper generates lower CO2 emissions when it takes at least one hour to read the document. Conversely, when it does not take at least one hour to read the document, using a laptop computer generates lower CO2 emissions as compared to when reading the document printed on paper.
For example, reading a paper or technical documentation often takes at least one hour. In such cases, reading a document printed on paper results in lower environmental impact compared to when using a laptop computer. Likewise, reading a document printed on paper generates lower CO2 emissions compared to when it takes about more than 30 minutes to read the document using a standard computer or more than 15 minutes using a high-performance computer. Therefore, choosing the paper or electronic devices in line with the time spent on reading a document reduces CO2 emissions.
Comparison of CO2 emissions generated by reading a document in a meeting
Example: A one-hour meeting
The following compares the CO2 emissions generated when a paper document is distributed with those when an electronic document is shown on the projector in a meeting. For a one-hour meeting with five participants where a ten-page document printed on both sides of paper is distributed to each participant, the total number of printed sheets is 25, and CO2 emissions are 189.5 g-CO2. In contrast, when the document is shown on the projector using a laptop computer for an hour, CO2 emissions are 191.4 g-CO2 (Table 3).
Table 3: Comparison of CO2 emissions
|A ten-page document is used in a one-hour meeting with five participants to compare CO2 emissions. (Note that g-CO2 is the unit for measuring CO2 emissions.)|
|Print the document on both sides of paper||5 sheets × 5 persons × (5 g-CO2 + 2.58 g-CO2) = 189.5 g-CO2
number of sheets × number of persons × (CO2 emissions of paper per sheet + CO2 emissions of a printer per sheet)
|Show the document on a projector using a laptop computer for an hour||(27.59 g-CO2 + 163.85 g-CO2) × 1 hr. = 191.4 g-CO2
(CO2 emissions of a laptop computer per hour + CO2 emissions of a projector per hour) × use time
Figure 2 shows the relationship between CO2 emissions and the number of participants. When a document is printed on paper and distributed to each participant, CO2 emissions increase in proportion to the number of meeting participants. However, when a laptop computer is connected to a projector to show a document, CO2 emissions increase in proportion to the time taken for the meeting, and do not depend on the number of participants. When more than 25 sheets of paper are to be distributed, less CO2 is generated by showing the document on a projector, and when 25 sheets of paper or less are to be distributed, less CO2 is generated by printing the document on paper. In actual meetings, many participants often use laptop computers connected to a projector to make presentations. In cases where all participants are assumed to bring laptop computers to the meeting room, CO2 emissions will increase in accordance with the number of participants. When there are 16 or more participants in such a meeting, CO2 emissions are lower when a document is shown on a projector than when the document is printed on paper and distributed to participants. In these ways, CO2 emissions are reduced by choosing paper or a projector in accordance with the number of sheets of documents distributed to participants and the number participants in a meeting.