I have been watching the blogposts of KDE Itinerary with some excitement and even though I did not have the chance to test it, I hopefully will soon. Seen the developments I thought it would be something which would belong into our time to calculate the CO2-footprint of a journey and allow to pay for their compensation if the emissions can not be avoided. I am not an expert, but quite sure that some of those services offer the necessary tools/api for doing the calculation and compensation.
I have been thinking about adding a year by year statistics view so you can track the effect of your personal effort to reduce environmental impact, which would need CO2 calculations as well. Integrating with compensation schemes could be a nice addition indeed. So far just ideas, I haven't done any research on this yet, but I certainly would consider this in scope.
The German perspective on this, a list of tested compensation projects: https://www.test.de/CO2-Kompensation-Diese-Anbieter-tun-am-meisten-fuer-den-Klimaschutz-5282502-5283299/ Myclimate seems to have an API Atmosfair which scored best in the test, I could not find anything.
Statistics page with CO2 impact estimation and year-by-year trends has been added now.