What is radiative forcing and why does it matter for flights?

Radiative forcing (RF) measures the change in Earth's energy balance caused by emissions. Aviation emits not just CO₂, but also NOx (creates warming ozone and cooling methane), water vapor (a greenhouse gas at high altitude), soot , and contrails (artificial cirrus clouds that trap heat). The IPCC estimates aviation's total climate impact is 2–4× higher than CO₂ alone.

Which radiative forcing multiplier should I use?

Conservative 1.9× (UK DEFRA), Standard 2.7× (Lee et al. 2021, IPCC-aligned, 100-year horizon — the default), Aggressive 3.0× (myclimate, 30-year horizon, net-zero 2050 aligned). The science is unsettled; range 1.9–3.0.

How are contrails different from CO₂ emissions?

Contrails are short-lived (hours to days) vs CO₂ (centuries), only form in ~5% of flight kilometers, and have a net warming effect of 0.03–0.06 W/m² globally — comparable to aviation's cumulative CO₂ warming.

Why do old flight calculators show much lower numbers?

Most calculators (Google Flights, ICAO, many airline tools) show CO₂ only . Our calculator shows CO₂-equivalent with RFI — typically 2–3× higher. The difference is missing non-CO₂ effects.

How does class of service affect my emissions?

Emissions are allocated by space: Economy 1.0×, Premium Economy 1.5×, Business 2.5×, First 4.0×. Flying business can triple your climate impact on the same flight.

Are short-haul flights worse per kilometer than long-haul?

Yes. Short-haul flights spend 25–30% of fuel on takeoff/climb (vs 5–8% for long-haul). Typical: short-haul 150–200g CO₂/pkm; long-haul 90–110g CO₂/pkm.

How accurate is the distance calculation?

We use the Haversine formula for great circle distance then apply a detour factor (1.07–1.15×) based on actual flight path data, ATC routing, and approach patterns. Each stop adds a full LTO cycle (~80 kg CO₂).

What are the best alternatives to flying?

High-speed rail (5–20g CO₂/pkm) for trips <800km, coach/bus (20–40g), EVs (20–50g), and remote work (0g). The calculator flags routes with viable train alternatives.

Flight Carbon Calculator + Radiative Forcing Multiplier | True Climate Impact

Flight Details

From (IATA code)e.g. LHR, JFK, NRTTo (IATA code)e.g. LAX, SIN, CDGTrip TypeRoundtrip doubles distance and emissionsClass of ServiceBusiness = 2.5× the space, 2.5× the emissions sharePassengersMultiplies total emissionsRadiative Forcing MultiplierAccounts for contrails, NOx, water vapor. 2.7× is the IPCC-aligned standard.Stops / LayoversEach stop adds an LTO cycle (~250 kg fuel)Aircraft TypeAuto-detect uses route-appropriate aircraft

Climate Impact: London → New York

✈️ London (LHR) → New York (JFK)

Great circle: 5,540 km · Flight path: 6,093 km · Aircraft: Boeing 787-9 · Roundtrip total: 12,187 km

Total Climate Impact: 1.69 t CO₂e

CO₂ only: 0.63 t · RFI multiplier: 2.70× · True impact: 1.69 t CO₂e

2.7× higher than old CO₂-only calculators show

Distance (total)

12,187 km

Fuel burn

70,685 kg

CO₂ emissions

0.63 t

Non-CO₂ (RFI-adj.)

+1.06 t CO₂e

Total CO₂e

1.69 t

Per km (CO₂e)

139 g/pkm

≈ months of avg citizen

2.4 mo

Offset @ $50/t

$85

Suitability of class

Economy

Emissions breakdown

CO₂ (fuel combustion): 0.63 t (37%)
Contrails + cirrus: 0.48 t (28%)
NOx (ozone − methane): 0.32 t (19%)
Water vapor: 0.16 t (9%)
Soot / aerosols: 0.11 t (6%)

⚠️ Old CO₂-only calculators show 0.63 t for this flight. Your true impact is 1.69 t CO₂e — 2.7× higher. If you offset the old figure, you cover only 37% of your actual impact. Recommended offset: 1.69 t CO₂e at $85 ($50/t benchmark).

Class	Allocation	CO₂e	vs Economy
Economy	1.0×	1.69 t	baseline
Premium Economy	1.5×	2.54 t	+50%
Business	2.5×	4.23 t	+150%
First	4.0×	6.76 t	+300%

Why your impact is 2.7× higher than CO₂ alone

CO₂ from fuel combustion (baseline)0.63 t

Contrails + contrail cirrus+0.48 t CO₂e

NOx (ozone warming − methane cooling)+0.32 t CO₂e

Water vapor at altitude+0.16 t CO₂e

Soot / aerosols+0.11 t CO₂e

Total with RFI 2.70×1.69 t

RFI source: Lee et al. 2021 (IPCC) · Time horizon: 100 years. Multiplier applied to the full flight distance.

Lower-impact alternatives & offsets

No viable train

No rail alternative

Consider video conferencing for business trips, or combining trips to reduce frequency.

Offset @ $15/t (low quality)

$25

Offset @ $50/t (high quality)

$85

Offset @ $200/t (DAC)

$338

Note: offsetting is not equivalent to not flying. The CO₂e is still emitted. Offsets are a last resort.

Complete guide to aviation's true climate impact

A roundtrip flight from London to New York emits approximately 1.0 tonne of CO₂ per passenger in economy class. Most calculators stop there. But the same flight also produces contrails that warm the climate, NOx that creates ozone, water vapor that traps heat, and soot that absorbs sunlight. When scientists add these up using the latest IPCC methodology, the total climate impact is roughly 2.7 tonnes of CO₂-equivalent — nearly triple the CO₂-only figure.

Why CO₂ is only half the story

Aviation contributes ~2.5% of global CO₂ emissions but 3.5–5% of total climate forcing when non-CO₂ effects are included. Contrails and contrail cirrus alone contribute warming comparable to aviation's cumulative CO₂. NOx creates tropospheric ozone (warming) and reduces methane (cooling) — net warming. Water vapor is a greenhouse gas with stronger radiative effect at altitude. Soot absorbs sunlight; sulfate aerosols reflect it.

The radiative forcing multiplier

Total Climate Impact (t CO₂e) = CO₂ Emissions (t) × RFI Multiplier. Key references: Lee et al. 2021 (IPCC-aligned, RFI = 2.7, 100-year horizon), DEFRA/BEIS (RFI = 1.9, conservative), myclimate/SCNAT 2021 (RFI = 3.0, 30-year horizon, net-zero 2050 aligned). The range 1.9–3.0 reflects scientific uncertainty, not error.

Methodology & data sources

IPCC AR6 / Lee et al. 2021 — aviation total climate impact, RFI = 2.7 (100-yr).
UK DEFRA/BEIS — conservative RFI = 1.9 for corporate reporting.
myclimate / SCNAT 2021 — RFI = 3.0, 30-yr net-zero 2050 aligned, DIN EN 16258.
ICAO Carbon Emissions Calculator — CO₂-only baseline, great circle + detour factors.
Haversine great-circle distance, 1.07–1.15× detour factor by route type.
CO₂ from jet fuel: 3.16 kg CO₂ per kg fuel (IPCC).

Frequently asked questions

Common questions

Radiative forcing (RF) measures the change in Earth's energy balance caused by emissions. Aviation emits not just CO₂, but also NOx (creates warming ozone and cooling methane), water vapor (a greenhouse gas at high altitude), soot, and contrails (artificial cirrus clouds that trap heat). The IPCC estimates aviation's total climate impact is 2–4× higher than CO₂ alone.
Conservative 1.9× (UK DEFRA), Standard 2.7× (Lee et al. 2021, IPCC-aligned, 100-year horizon — the default), Aggressive 3.0× (myclimate, 30-year horizon, net-zero 2050 aligned). The science is unsettled; range 1.9–3.0.
Contrails are short-lived (hours to days) vs CO₂ (centuries), only form in ~5% of flight kilometers, and have a net warming effect of 0.03–0.06 W/m² globally — comparable to aviation's cumulative CO₂ warming.
Most calculators (Google Flights, ICAO, many airline tools) show CO₂ only. Our calculator shows CO₂-equivalent with RFI — typically 2–3× higher. The difference is missing non-CO₂ effects.
Emissions are allocated by space: Economy 1.0×, Premium Economy 1.5×, Business 2.5×, First 4.0×. Flying business can triple your climate impact on the same flight.
Yes. Short-haul flights spend 25–30% of fuel on takeoff/climb (vs 5–8% for long-haul). Typical: short-haul 150–200g CO₂/pkm; long-haul 90–110g CO₂/pkm.
We use the Haversine formula for great circle distance then apply a detour factor (1.07–1.15×) based on actual flight path data, ATC routing, and approach patterns. Each stop adds a full LTO cycle (~80 kg CO₂).
High-speed rail (5–20g CO₂/pkm) for trips <800km, coach/bus (20–40g), EVs (20–50g), and remote work (0g). The calculator flags routes with viable train alternatives.