Transportation: The Elephant on the Plane

When I started tracking my carbon footprint, one category dominated all others: transportation. Specifically, aviation.

This post breaks down the carbon costs of different transport modes and explores the uncomfortable mathematics of modern travel.

The Numbers

Carbon Emissions by Mode

Per passenger per kilometre (kg CO2e):

Source: UK Government conversion factors

Real Journey Comparisons

London to Manchester (320km)

Train: 6x less carbon than flying.

London to Paris (450km)

Train: 4x less carbon, faster door-to-door.

London to New York (5,585km)

No good alternative exists. This is the problem.

Why Aviation Dominates Footprints

Distance + Carbon Intensity

• Modern life often requires long-distance travel
• For distances >1,500km, flying is often only option
• A single long-haul flight can equal a year of careful low-carbon living

The Academic/Professional Trap

My field (computer science, HCI) expects:

• International conference attendance (3-4/year typical)
• Global research collaboration
• Visiting lectures and keynotes
• External examining

Each = 1-2 return flights. Total: 5-8 flights/year. This alone puts you at 3-5 tonnes CO2e.

The Efficiency Paradox

Flying is carbon-intensive per km, but time-efficient. Train from Manchester to Berlin: 15+ hours. Flight: 2 hours.

When time is valuable (professionally), flying wins despite carbon cost. This is a systemic problem, not individual failing.

Modal Choice Decision Tree

Distance < 500km

Best: Train (electric where possible)
Acceptable: Car (if shared, EV preferred)
Avoid: Flying

Rationale: Train often competitive on time, vastly better on carbon.

Distance 500-1,500km

Best: Train (plan journey time)
Consider: Overnight train (makes time cost bearable)
Last resort: Flight (if truly time-critical)

Rationale: Carbon difference substantial, train usually feasible with planning.

Distance > 1,500km

Reality: Flying often only option
Mitigation:

• Question if journey necessary
• Combine trips (multi-purpose)
• Extended stays (justify carbon cost)
• Virtual alternatives where possible

The Commute Question

Daily Impact

Manchester to university: 8km each way

Cycling vs. solo driving: 620kg/year difference

That’s equivalent to a return flight to Athens.

Feasibility Factors

Not everyone can cycle:

• Distance (8km manageable, 30km not for most)
• Safety (infrastructure quality matters)
• Physical ability
• Weather (some climates/seasons prohibitive)
• Cargo (shopping, children)

But where feasible, commute choice compounds over years.

The Electric Vehicle Question

Current Reality (2019)

Average EV: 0.053 kg CO2e/km (UK grid mix)
Petrol car: 0.192 kg CO2e/km

EV: 72% reduction in running emissions.

But manufacturing EV battery: 5,000-10,000 kg CO2e upfront.

Breakeven: ~50,000-100,000 km depending on electricity source.

Future Potential

As grid decarbonises, EV emissions fall further. By 2030, potentially 90% reduction vs. petrol.

But still worse than:

• Not owning car
• Public transport
• Cycling

EVs aren’t carbon-free, just lower-carbon than alternatives.

Policy Implications

Individual choice matters, but system design matters more:

What Helps

• Cheap, fast, frequent trains
• Safe cycling infrastructure
• EV charging networks
• Remote work acceptance
• Virtual conference platforms

What Hinders

• Expensive rail vs. cheap flights
• Car-centric city design
• Professional pressure to attend in-person
• Time penalties for low-carbon choices

Personal Approach

My transportation hierarchy:

1. Avoid - Is journey necessary?
2. Virtual - Can it be online?
3. Cycle - For local (<10km)
4. Train - For regional/national
5. Car - If shared, or no alternative
6. Fly - Only if no reasonable alternative

Since adopting this in 2019:

• 70% reduction in transport emissions
• Maintained professional activities
• Actually enjoyed train journeys
• Better fitness from cycling

Not perfect. Still fly occasionally. But vastly better than pre-2019.

The Uncomfortable Truth

For many of us, transportation – particularly aviation – is the largest controllable part of our footprint.

And unlike heating or electricity (where we can switch to renewables), flying has no clean alternative yet. Biofuels and electric planes are decades away at scale.

So our choices are:

1. Fly less (individual action)
2. Demand better alternatives (collective action)
3. Accept slower travel (time trade-off)
4. Restrict activities (lifestyle change)

Or some combination.

There’s no easy answer. But awareness is the first step.

And tracking, as these audits show, makes the invisible visible – and the abstract concrete.