Transportation emissions - challenges with freight emission factors

The main issue with freight emission factors, usually given as kg CO2 per tonne kilometre (tkm), is that they are consolidated numbers that are based on many assumptions. This leads to a lack of transparency and usability because there are wide international differences in the nature and efficiency of freight transport operations, in the primary source of electricity and in the condition of transport infrastructure. For instance, the actual CO2 emissions of (electric) rail freight depend primarily on the CO2 intensity of the electricity production. This intensity may vary by factors of >10 between different European countries. Another example are inland waterways where a barge is moving either upstream or downstream which may change the fuel consumption by over 50%.*

Load factors also have significant impacts on CO2 emissions per tkm because load factors depend on route directions and on the type of cargo. For instance, (air) freighters going from Asia to Europe have load factors of over 90% whereas reverse directions have load factors that can be 2-3 times lower. Very light weight cargo with volume as the limiting factor needs more transport vessels and in consequence more CO2 will be emitted per kg of cargo.

Using a generic/global CO2 emission factor can therefore be somewhat ruthless and it may lead to substantial errors when trying to compare different options, especially on a granular level. However, high level emission factors are still suitable to compare the average carbon intensity amongst different modes of transport (see graphic). Airfreight has obviously by far the highest CO2 emissions per tonne kilometre, but is also the source with the widest variance in available credible data. Sea freight is the energy efficient way of transport and is in fact over 50 times less CO2 intensive than air freight.

Source:

* IFEU (2005) EcoTransIT: Ecological Transport Information Tool Environmental Methodology and Data.