When shipping long distance — from China to the UK for example — there are two main options: air freight and sea freight. Whilst they both serve the same purpose, the consequences of each are vastly different. Sea freight has a smaller carbon footprint than air freight. Air freight is quicker than sea freight. Sea freight is cheaper than air freight.
As a business wanting to make the best decision, you should weigh up all of the differences between air and sea. It's not enough to only focus on speed. Or environmental impact. If you do, you could risk missing the big picture, and that could be costly.
Let's dive deeper into three critical things to consider.
Different forms of transport produce different amounts of greenhouse gases. And between air freight and sea freight, the difference is staggering. We leveraged our life cycle assessment data* to compare the environmental impact of both for an example shipment travelling from China to the UK. It showed that using air freight would produce 31 times more emissions than sea freight.
For more context, a freight train produces 1.6 times as many emissions as a cargo ship, and a truck 10 times as many. Put simply, sea freight has the smallest carbon footprint of all major forms of long-distance freight. Air has the largest.
What makes matters worse for air freight is altitude, where emissions have a more complicated impact. Carbon dioxide, for example, often has a more severe warming effect on the atmosphere at altitude than it does when emitted at ground level. Vapour trails too have their own warming effect, adding to the already harmful wake of air freight.
In other words, the environmental impact of air freight is more than the emissions a plane leaves behind. At altitude, the effects of those emissions are multiplied. So, whilst a straight comparison between air and sea CO2 emissions is telling enough, the true cost to the planet is likely to be much higher.
If you need to ship products across the world, and you want to reduce your business' carbon footprint, sea freight has to be a priority. That said, cargo ships still have a long journey ahead before they can be considered sustainable, but there are promising signs. In 2020, new worldwide fuel laws came into action, cutting the legal sulphur content in shipping fuels by 70%. Less sulphur means less air pollution, and that means less acid rain and cleaner air for the communities that live around ports. Together with new fuels on the horizon — such as biofuels and hydrogen — sea freight is heading in the right direction.
For shipping, time might be important for three reasons. First, you want to pass on fast delivery times to your customers as value. Second, demand for your product fluctuates and you need the option of getting stock fast. Third, your product might need to be shipped quickly because of what it is. Perishables, for instance, will degrade over time, so it's important to first consider what it is you're shipping as this may define how you ship it.
In any case, if time is critical for your product, air freight will always deliver much quicker than sea freight. Using our example shipment again, transporting it from China to the UK in a cargo ship could take 50 to 60 days. If you sent the same shipment on a plane, it would be with you in 3 to 5 days.
Sea freight also arrives at ports, and they're often further away from warehouses, offices and customers than airports. Shortening the distance between these logistical ingredients is one way to streamline your operations and reduce complexity.
It's worth mentioning too that whilst both cargo ships and planes are affected by similar delays, such as extreme weather events, air freight is usually quicker to get back on track. Planes are often rerouted or rescheduled the on same day, whereas for cargo ships it can take days.
So, sea freight is much slower. But that doesn't mean it's a worse choice for your business, or that you can't meet the market demand for speed. If your product is suitable for sea freight, and you order stock in advance, long transit times may not impact your business as much as the numbers suggest. It just takes some planning.
Generally, air freight is much more expensive than sea freight. For the shipment we've been using, sending it via air would be 3 to 4 times more expensive than if you sent it via sea. Others estimate air freight as high as 6 times more expensive than sea freight.
The main reason for this is that planes are smaller than cargo ships, and because of that smaller capacity, space comes at a premium. There's just not the same opportunity to aggregate orders and benefit from shipping in bulk. For large shipments, this means sea freight is the cheapest option, by far.
If you're shipping small quantities of lightweight items, the cost difference does shrink. That's because weight is a more dominant cost factor for air freight. And with a smaller margin, you might justify shipping air when balanced with other factors. But, even then, air is likely to be more expensive, and there should be a firm rationale behind choosing to pay such a price.
For long-distance shipping, sea freight is the most sustainable option — that's certain. It offers a chance to drastically reduce your product's carbon footprint whilst also cutting costs. Sea freight will take longer than air freight to get your product from A to B, but with smart planning, that extra time doesn't have to be a constraint.
As much as we prioritise shipping sea over air, this doesn't mean everything should be shipped that way. If your product demands it, air freight might be the only viable choice. Or you might be able to use both. What is crucial, whichever you choose, is that you consider the big picture. Only then can you make an informed decision.
To reduce the impact of everything we ship, we group orders together to optimise freight space. We always prioritise sea freight over air freight, and offset the CO2 emissions of all our shipments.
*This Life Cycle Analysis was based on a typical client shipment of e-commerce mailer boxes, travelling from China to the UK. The analysis includes the sea or air freight transit to the UK, as well as delivering the product from an airport or port to our warehouse in Manchester.
The analysis goes deep into each freight component, capturing the full impact of the shipment. This means we included all non-direct factors such as the construction of the aircraft, the maintenance of the container and the construction of the roads on which the truck travelled. The impact was modelled using our internal LCA technology and the freight datasets in Ecoinvent.
Source: Wernet, G., Bauer, C., Steubing, B., Reinhard, J., Moreno-Ruiz, E., and Weidema, B., 2016. The ecoinvent database version 3 (part I): overview and methodology. The International Journal of Life Cycle Assessment, [online] 21(9), pp.1218–1230. Available at: http://link.springer.com/10.1007/s11367-016-1087-8 [Accessed 01062021]