A while ago I was shown online a page where you could input something like the following:
2 passengers ex LHR
3 passengers ex JFK
4 passengers ex SIN
5 passengers ex HKG
The tool would then calculate where you should all meet to minimize the CO2 emissions - based purely on distance flown (so, please, no replies telling me how futile it is as different aircraft and different engines have different emissions and so on

)
Does anyone out there know the webpage for this? I've searched here back to 2005, and googled this, but without success so far. Anyone knows about this planning tool?