From the Exosphere
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From the Exosphere

Whose emissions are those? A spotlight on international bunker fuel emissions

Data scientist Bryan Field looks at who’s supposed to be responsible for the emissions caused by international shipping and aviation and what’s being done to reduce them

Photo by shawnanggg

International bunker fuels — it doesn’t sound like an interesting topic for a blog but trust me on this one, it’s more interesting and important than you might think.

“Bunker” fuels are fuels used for international transport, specifically in planes and ships, and so they’re a critical component of the global economy. International transport is a key enabler of international trade and is critical for New Zealand — for example, we export milk powder and logs, we import oil and cars, and we rely on many international tourists coming here to spend their money.

But who’s responsible for the emissions that result from these activities? The answer is no-one. When countries report their total greenhouse gas emissions each year, that number excludes emissions from international bunker fuels. These are instead reported as “memo items” in each country’s National Greenhouse Gas Inventories — that is, as something to note, but not included in the hard numbers that each country is responsible for.

How significant are bunker fuel emissions?

If no-one’s responsible for these emissions, they can’t be that big, right? Well, international bunker fuel emissions are more significant than you might think.

Take a look at the graph below — it shows total gross greenhouse gas (GHG) emissions for the 38 developed countries, New Zealand included, who have signed the UN Framework Convention on Climate Change (UNFCCC) and so are taking responsibility for mitigating climate change. (By the way, the unit “MtCO₂e” is “million tonnes of carbon dioxide equivalent”.)

International bunker fuel emissions compared with total GHG emissions and total energy emissions for UNFCCC Annex I countries, 199–2019. (Source: UNFCCC, 2021)

This is in fact two graphs overlaying each other, allowing us to compare different trends. First, the blue and orange lines (to be read against the left-hand scale up to 20,000 MtCO₂e) show, respectively, total GHG emissions and energy sector emissions. (Remember that “energy sector emissions” doesn’t just mean the energy industries like electricity generation, it’s also all forms of transport — basically all emissions from consuming energy.) As you can see, both total GHG emissions and energy sector emissions have been going down over time.

But look at the grey line (to be read against the right-hand scale up to 800 MtCO₂e) — that’s international bunker fuel emissions, and they’ve been increasing over the last 30 years, from 373 MtCO₂e in 1990, to 593 MtCO₂e in 2019.

And it’s not just that these bunker fuel emissions are increasing in absolute terms — they’re also increasing as a proportion of total GHG emissions, from 2.0% in 1990, to 3.6% in 2019.

So, international bunker fuel emissions aren’t tiny — in fact if they were a country they would be the eighth largest, with more emissions each year than Australia (593 MtCO₂e vs 545 MtCO₂e). What’s more, these emissions are growing over time.

Are ships or planes the problem?

International bunker fuel emissions include both shipping (“international navigation”) and aircraft (“international aviation”).

The graph below shows that while shipping emissions from all of the 38 UNFCCC Annex I countries peaked in 2007 and have been flat since 2012, aviation emissions have continued to increase. They’ve grown by 128.2% since 1990, whereas shipping emissions grew by only 12.3% over the same period.

International aviation emissions and international navigation
emissions for UNFCCC Annex I countries, 1990–2019.
(Source UNFCCC, 2021)

What’s being done to reduce bunker fuel emissions?

Among international organisations, responsibility for reducing international bunker fuel emissions sits with two UN bodies — the International Maritime Organization (IMO) and the International Civil Aviation Organization (ICAO).

Back in 2009 a report by the European Federation for Transport and the Environment questioned the effectiveness of both the IMO and ICAO in reducing emissions, basically accusing them of lots of talk and not much walk:

“Studies and discussions have followed for almost 12 years but neither organisation has agreed one single binding measure to control emissions.” (page 4)

Action by international bodies to reduce shipping emissions

Since 2009, it seems the IMO has listened. In particular, they’ve improved international regulations for bunker fuels (mostly reduced sulphur content) and adopted a non-binding agreement to reduce international shipping emissions by 50% below 2008 levels by 2050, according to Maria Gallucci from the Yale School of the Environment.

The IMO’s strategy to reduce greenhouse gas emissions includes three main goals:

· “carbon intensity of the ship to decline through implementation of further phases of the energy efficiency design index (EEDI) for new ships”

· “carbon intensity of international shipping to decline”

· “GHG emissions from international shipping to peak and decline” (the emissions reduction goal mentioned above is part of this).

If the graph above is any indication, the IMO’s strategy is having a positive effect on emissions from shipping — emissions from international navigation for UNFCCC signatory countries in 2019 were down by 15.3% from 2007.

Action by international bodies to reduce aircraft emissions

The ICAO — the International Civil Aviation Organization — also has several programmes underway to help reduce greenhouse gas emissions from international aviation.

The graph below projects the difference that various measures will make in reducing emissions. Projected emissions if no action is taken are shown by the upward curving line at the top of the piece of blue. The graph shows that a combination of technological advances, operational improvements, and two current programmes would keep emissions on a flat line at around 550 MtCO₂e despite heavy projected growth in aviation — in other words, that growth would be carbon-neutral.

Projected impact of ICAO’s actions to reduce greenhouse gas emissions. (Source: ICAO website)

The two programmes mentioned are Sustainable Aviation Fuels, and CORSIA. The first one is fairly self-explanatory, while CORSIA stands for “Carbon Offsetting and Reduction Scheme for International Aviation” — basically, it’s a certified scheme for measuring, reducing, and offsetting the CO₂ emissions from aviation.

Offsetting is certainly part of the answer here — biofuels aren’t yet ready for use in international aviation, and electric planes are probably only suitable for short-haul flights. Data on CORSIA is due to be released by the ICAO later this year, so watch this space!

The ongoing COVID-19 pandemic has meant massive reductions in international flights, and consequently in emissions. But the aviation industry will need to consider ways to reduce emissions from international travel as the world returns to normal.

Action by individual countries and companies

So what’s being done at the country or company level to reduce international bunker emissions?

In 2019 my colleague Kevin Jenkins wrote about some of the notable developments happening with electric boats, ferries and ships, as well as other low-emissions fuels. For example, container shipping giant Maersk wants to have commercially viable carbon-neutral ships in operation by 2030. At the country level, Norway has been a leader, and has made a major research and development investment in hydrogen fuels.

But although there are some positive initiatives like those aimed at helping wean the world off bunker fuels, there’s a systemic barrier here — a problem of attribution at the country level that needs to be settled before the world can make qualitative progress in reducing international bunker fuel emissions.

So how do you meaningfully attribute shares of “international” emissions to individual countries?

Allocating responsibility to individual countries

The problem allegedly comes down to difficulties of attribution. The IMO says:

As already acknowledged by the Kyoto Protocol, CO₂ emissions from international shipping cannot be attributed to any particular national economy due to its global nature and complex operation.

It’s true that shipping and aviation are both global and complex, but I disagree that shipping and aviation emissions can’t be attributed to particular national economies.

The solution is simple. Every flight and shipping route has a departure port and an arrival port, and generally planes and ships fuel up at the departure port. The simplest way to allocate emissions to national economies is to allocate them to the country of the departure port.

First of all, this is where the fuel is sold, so it’s easy to measure. Also, any plane or ship that leaves a port has arrived from somewhere else, and so making them responsible for departing flights and ships seems arbitrary, countries also get the benefits of arriving flights and ships, for which other countries are responsible. So globally this would be a fair allocation — unless countries are accumulating ships and/or planes.

So what’s New Zealand’s share of bunker fuel emissions, and what are we doing about them?

It’s this method of allocating particular voyages or flights to the country of the port of departure that New Zealand, like all UNFCCC countries, uses to quantify its share of international bunker fuel emissions. It’s those numbers that are included as memo items in New Zealand’s GHG inventory — and excluded from our national total for gross greenhouse gas emissions.

The graph below — again it’s really two graphs — shows that while New Zealand’s total GHG emissions (and energy sector emissions) have been flat since 2005, our international bunker fuel emissions have grown significantly. They’ve increased by nearly half (45.8%) since 2005, and have more than doubled since 1990 (a 106.8% increase).

What’s more, New Zealand’s international bunker fuel emissions make up a larger share of our total emissions (6.0%) than for all 38 of the UNFCCC Annex I countries considered together (3.5%). This is not surprising given we’re a small group of islands in the South Pacific that relies heavily on international trade.

New Zealand’s total emissions, energy sector emissions, and international bunker emissions, 1990–2019. (Source: Ministry for the Environment, 2021)

Action here in Aotearoa

Our own Air New Zealand is part of CORSIA, the carbon offsetting and reduction scheme. Beyond that New Zealand doesn’t have any initiatives that directly affect international shipping and aviation. However, we do have some domestic examples of low-emissions technologies for aviation and navigation:

· Wisk Aero has signed an MoU with the New Zealand Government to trial their autonomous all-electric air taxi in Canterbury (for those interested here’s a video)

· Fullers, the Auckland ferry operators, are collaborating with EV Maritime and Auckland Transport to develop battery-electric fast ferries for Auckland harbour

· East by West Ferries are about to launch an electric ferry for commuters in Wellington — they’re currently putting the ferry, Ika Rere, through sea trials

· Sounds Air are looking to buy electric aircraft for zero-emissions regional travel in New Zealand, with the first flights expected in 2026

· ElectricAir recently flew its Pipistrel Alpha Electro aircraft across Cook Strait, in a 40 minute flight.

These are all only small steps, but they will be important proofs of concept.

Countries need to start taking responsibility for the impact of international aviation and shipping

Action to keep global warming to within 1.5 ⁰C as projected by the Paris Agreement needs to be holistic and comprehensive. And as part of that, we need to start including international bunker fuel emissions within National Greenhouse Gas Inventories so that countries have direct incentives to reduce them.

Excuses for not including them are weak. We all know that “What gets measured is what gets done”, so continuing to include these emissions only as memo items and not within total gross emissions is at odds with the intent of the Paris Agreement.

When we ask our governments “Whose emissions are those?”, the answer shouldn’t be “Not ours”.

Photo by James Coleman




From the Exosphere is a platform for sharing thoughts from the team at MartinJenkins. The exosphere is the last layer of atmosphere before space, offering an unrivalled view of our blue planet and where we might go next.

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