Since I ate a lot of food, I asked to myself if maybe a train (dividing cost between all passenger) was more green than me!
A train typically uses electricity. The emissions of electricity on the greenest grids are typically around 50 g / kWh produced. In the near future I think we can even reach zero with hydrogen energy storage and renewables.
However, a train is a heavy object. A human on a bicycle travels at around 150 watts at a speed of 20 km/h, i.e. 7.5 watt-hours per kilometer. Compare that to an electric car using around 180 watt-hours per kilometer.
A human is a thermal engine with 25% efficiency. So a human needs 30 watt-hours per kilometer of food energy. This is 25.8 kcal, or 7.6 grams of pasta per kilometer.
Creating a kilogram of pasta produces 1.3 kilograms of fossil CO2 (plus the non-fossil CO2 that isn't counted because the plant has sequestered it from the atmosphre). So traveling on a bicycle at the minimum produces 10 grams of CO2 per kilometer. Of course a human could have a more varied diet.
An electric car would be 180 watt-hours per kilometer or 9 grams of CO2 per kilometer on the greenest grids already today. So an electric car weighing 2000 kg is already today more climate-friendly than a bicycle weighing 100 kg with the cyclist riding on it.
A train today consumes 16 watt-hours per kilometer per passenger. So a train already today requires less primary energy than a bicyclist. On the greenest grids today, a train thus produces around 0.8 g / passenger-kilometer.
Of course on the dirtiest grids you can multiply all amounts by 20. So an electric car would be 180 g / km and a train would be 16 g / passenger-km. So in a really dirty grid a train would produce more CO2 than a bicyclist on a really green diet. However, most cyclists don't eat only pasta but eat a small portion of meat as well, so we can safely conclude that in 99.9% of cases a train is more green than a cyclist.
Electric bicycles with current regulations won't help much by the way. On an electric bike, over half of the energy comes from the human cyclist due to the 25 km/h requirement, and only less than half from the electricity. This is because a typical cyclist on flat ground is already traveling at more than 25 km/h. To make electric bikes truly green, the 25 km/h requirement at which the electric assist needs to be cut off has to go away.