After looking at this data

https://ourworldindata.org/travel-carbon-footprint

one wouldn’t feel bad traveling short-haul flights in comparison to land based options.

There are three factors that go into the carbon footprint while traveling:

• carbon emissions per kilometer
• distance between locations
• passenger count of vehicle

And then there are personal factors like:

• cost of travel
• duration of travel

Considering that on average air travel is always the shortest option among the rest, the hypothesis would be that carbon emissions on that factor would be equivalent.

Let $a, b$ be vehicles. Let $c_a, c_b$ be carbon emissions in g/km with $c_a > c_b$ and $d_a$ be the distance bound to vehicle $a$. Then

\[d_b = \left(\frac{c_a}{c_b} - 1\right)d_a\]

is the allowance of kilometers for the vehicle bound to $q$ before a carbon equivalence is made.

Another factor is the capacity amount of passengers, let’s say that the average short-haul flight has 180 passengers, the average long distance bus 60 passengers and the average long distance train 2550 passengers (30 cars times 85 passengers). This quickly solidifies that traveling by train is the cleanest option. Assuming each vehicle is fully booked.

Let’s extend the upper equation with passenger count denote with $p$. Then

\[d_b = \frac{c_a}{c_b}\frac{p_b}{p_a}d_a\]

is vehicle’s $b$ allowance in kilometers before equivalence.

In conclusion, just because it seems like a vehicle is carbon emission wise worst off on a g/km basis, does not have to mean that case holds up for the complete trip.