• Trees: The percentage of a tree (or trees) used to make the paper.
  • Carbon: The amount of CO2 (green house gas equivalent) that was released in the process of manufacturing and delivering the paper.
  • Energy: Represents the impact in terms of the equivalent impact of running a 60W bulb for a period of time.

  
Field Description
Trees
 This value corresponds to percentage of a tree that has gone into making the paper. The value assumes the user is printing on standard A4 or Letter sheets and 80,500 sheets make up a tree [a]

This value is set by the config key: environment.sheets-per-tree

Carbon
 This value corresponds to greenhouse gases released in the production of the paper (CO2 equivalent). The value assumes that the user is printing on standard A4 or Letter sheets and one sheet equals 8.6g CO2 [b].

The default value takes in account CO2 produced as a byproduct of the paper production only. It does not take into account the power consumed by the printer or power associated with the ink / toner use and production. Finding referenced figures on these values is difficult, and one could argue that the printer power consumption is not a function of the user's usage as the printer would be there consuming power even if they choose not to use the device.

This value is set by the config key: environment.co2-grams-per-sheet

Energy
 This value represents the manufacturing energy used to produce the paper. The energy value is represented by relating it to the equivalent energy consumed by a standard light bulb. This provides users with a real world understanding of the value. This value assumes the user is printing a standard A4 or Letter sheet and that the manufacturing cost per sheet is 17Wh [c]. This is an appropriate amount for virgin office paper. 12Wh is more appropriate for 100% recycled paper [d].

This value is set by the config key: environment.watt-hours-per-sheet

 
[a] A single tree can produce about 80,500 sheets of paper according to How Much Information? 2003 filed by University of California at Berkeley,
http://www2.sims.berkeley.edu/research/projects/how-much-info-2003/print.htm.

[b] Office paper produces 0.53 metric tons of carbon equivalent (MTCE) per ton of paper, according to the USA EPA report Greenhouse Gas Emissions From Management of Selected Materials in Municipal Solid Waste, 1998, p26, here.

This amount is equal to 1.9 metric tons of CO2. The Environmental Energy Technologies Division of the U.S. Department of Energy indicate that there are about 220,000 paper sheets in a ton: http://eetd.lbl.gov/paper/ideas/html/copyfactsM.htm.

[c] According to the Environmental Energy Technologies Division of the U.S. Department of Energy, the manufacturing cost of virgin office paper is 17 Watt hours:
http://eetd.lbl.gov/paper/ideas/html/issues.htm.

[d] According to the Environmental Energy Technologies Division of the U.S. Department of Energy, the manufacturing cost of 100% recycled office paper is 12 Watt hours: http://eetd.lbl.gov/paper/ideas/html/issues.htm.