A 'virtual' meeting is a lot 'greener' than traveling long distances and helps to reduce your carbon footprint (the impact your activities have on the environment, especially greenhouse gasses).
The 'carbon calculator' shows the approximate amount of CO2 that aircraft flying people to and from the meeting would have produced.
For those interested here is a description of how the figure is calculated:
We loop through all of the attendees of the meeting and calculate how far each of the other attendees would have to travel to get to their location. From this we choose the shortest of these totals, to find the person the attendees could have chosen to travel to, in order to travel the shortest distance. Distances are calculated using the 'great circle' distance on the Earth's surface (i.e. we assume a 'sphere' and it is the shortest surface distance).
The figures for flights were taken from the web page: http://www.climatecrisis.net/takeaction/carboncalculator/howitwascalculated.html
We use the figures listed on this web page to calculate the amount of CO2 that would have been used. The appropriate consumption figures are then applied to each individual's journey. Finally the total is doubled because presumably the trip would include a return journey!
Some of the assumptions and inaccuracies:
1) IP location = person location
2) World is spherical
3) People would be making the trip to the optimum person
4) People make a no-stops direct flight to the person
5) The trip is assumed to be a flight
6) The fuel effeciency consumption figures from the web site are only approximate? (see the link above for details)
7) A few IP's of attendees will not always be resolved to a location and consequently in such a case their trips are not included