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Study projects net cooling of climate from ship emissions through 2050

Shipping-induced global temperature change in 2050 using different parameterizations of Indirect Aerosol Effect (IAE). Credit: ACS, Lund et al. Click to enlarge.

A recent study by an international team calculated that shipping causes a net cooling of climate across all parametrizations of the indirect aerosol effect (IAE) and scenarios throughout the period 1900−2050. This continued shorter-term cooling response caused by certain emissions does not negate the necessity for reductions in CO2 emissions, which are crucial to limiting the long-term warming impact of the sector, the researchers cautioned.

The team from Center for International Climate and Environmental Research—Oslo (CICERO); Deutsches Zentrum für Luft- und Raumfahrt (DLR); University of Hawaii at Manoa; and Manchester Metropolitan University (UK) estimated the global-mean radiative forcing (RF) and total net surface temperature change from the shipping sector for a range of emission scenarios using a simple climate model (SCM). The paper is published in the ACS journal Environmental Science & Technology.

A recent study commissioned by the International Maritime Organization (IMO) estimated total emissions of 1046 Tg CO2 yr−1 from shipping in 2007, corresponding to 3.3% of the total anthropogenic CO2 emissions in that year. Of that, international shipping accounts for 83% (870 TgCO2 yr−1 of the total ship emissions in 2007.

In addition to CO2, other compounds such as ozone (O3) precursors (nitrogen oxides (NOx=NO+NO2), carbon monoxide (CO), and volatile organic compounds (VOCs)) and aerosols such as black carbon (BC) and organic carbon (OC) are emitted by ships. Shipping is an important source of sulfate (SO4) through oxidation of emitted sulfur dioxide (SO2) because the fuel sulfur content is usually high, averaging around 2.7% by mass. Other than these emissions from combustion associated with main engines and boilers, there are also emissions of ozone-depleting substances (CFCs/HCFCs/ HFCs) from refrigerant and air conditioning systems. The O3 precursors, SO2, and aerosol emissions have effects on atmospheric composition and climate and can affect human health and cause regional pollution and acidification.

We focus here on the present-day and anticipated future climate impacts of ship emissions in terms of their contribution to global-mean radiative forcing (RF) and changes in surface temperature. The mechanisms involved are complex, and the emissions can result in both warming (positive RF) and cooling (negative RF) effects: (1) CO2 gives a positive RF; (2) NOx results in production of tropospheric O3 (positive RF) and a reduction of ambient CH4 (negative RF) [Reductions in CH4 leads to a longer-term reduction in O3 through changes in the atmosphere’s oxidation capacity (negative RF)]; (3) direct aerosol effect of OC and SO4 particles (negative RF); (4) direct aerosol effect of soot particles and reduced surface albedo when deposited on snow/ice covered surfaces (positive RF); (5) formation or change in low-level cloud properties, so-called indirect aerosol effect (negative RF).

—Lud et al.

Prior work on the overall RF (including the highly uncertain indirect aerosol effect) of shipping in 2000 from preindustrial suggested that shipping has a net cooling impact today. The authors used a range of emission scenarios for shipping, consistent with the new regulations on nitrogen oxides (NOx) and sulfur dioxide (SO2) from the International Maritime Organization to determine the induced global-mean radiative forcing and temperature change.

Using on a complex aerosol-climate model, they developed and tested new parametrizations of the indirect aerosol effect (IAE), resulting in their finding of a net global cooling impact throughout the period 1900–2050 across all parametrizations and scenarios.

However, they noted, the wide range across parametrizations emphasizes the importance of properly representing the IAE in SCMs and to reflect the uncertainties from complex global models.

Because of the expected reductions in SO2 and NOx emissions reflected in the scenarios, the cooling impact of shipping is initially reduced. However, in the IMO scenarios the increase in activity outweighs emission reductions from more stringent regulations and the cooling effect strengthens again despite increases in CO2. In the RCPs [Representative Concentration Pathways], reductions in SO2 and NOx continue up to 2050 and beyond and result in a continued weakening of the cooling. If current regulations are insufficient to continuously reduce emissions of SO2 and NOx, the net impact of shipping is likely to be a continued cooling until 2050. This will also exacerbate the significant additional negative impacts of shipping, such as acidification and health-related problems.

However, if short-lived cooling species are reduced, the long-term warming due to CO2 dominates, and the net temperature change becomes positive. As has been emphasized in several previous studies, a continued cooling response does not negate the necessity for reductions in CO2 emissions, which are crucial to limiting the global climate impact of the sector since the warming effect of CO2 is long-lived.

—Lund et al.


  • Marianne Tronstad Lund, Veronika Eyring, Jan Fuglestvedt, Johannes Hendricks, Axel Lauer, David Lee, and Mattia Righi (2012) Global-Mean Temperature Change from Shipping toward 2050: Improved Representation of the Indirect Aerosol Effect in Simple Climate Models. Environmental Science & Technology 46 (16), 8868-8877 doi: 10.1021/es301166e



What would be the 'cooling effect' if the 1B ICEVs were converted to BEVs?

Nick Lyons

I'd be interested to know if their models take into account the effect of black carbon on snow cover and ice melting at high latitudes. Climate is changing (warming) fastest at the poles, and the changing albedo from black carbon deposits is one of the reasons.


Actually Nick BC would be a minor effect compared to the change in albedo that is already happening up north. White, reflective sea ice is becoming dark, absorbing opean water;


Sorry for the "opean" typo - replace with "open" or "ocean" or both.


Arctic ice melting at an accelerated rate is having a significant effect of the climate. Tornado in NYC is just one of the visible effect. We have used more energy to cool the house in the last four months than we used to keep it warm last winter. That's something new North of the USA border.

The naysayers and the fossil fuel advocates may not agree but sooner or latter they will have to open their eyes and ears and take note.

The American dream is based on unsustainable exponential growth in energy, population, food production/consumption, industrial production, credit market debts, environment and economy, all leading to a melt down that could make 1929 look like a minor ripple.

Wise people with $$$ will protect their wealth with gold/silver, oil/NG, pipelines, utilities, medical, food production and processing, water, wind/solar energies and by investing 70% out of the country.


These ships are outdated technologies, polluting and maintened by big oil capital to make even more profits on their main petrol business where the internationnal profits are deposited in fiscal paradises banks.

I said many times to build hydrogen fuelcell ships with a water electrolyzer inside the ship to make hydrogen gas while travelling.


build hydrogen fuelcell ships with a water electrolyzer inside the ship to make hydrogen gas while travelling

If that's the totality of your idea you've just described a perpetual motion machine, and that would be impossible.


The "net cooling" effect of sulphate aerosols actually accelerates the rate of ocean acidification. No matter how you slice it, there is "net harm" created by burning fossil fuels.


and you could add burning bio-fuels...


ai_vin, you keep forgetting that AD is just comic relief.  He/she/it makes about as much sense as a Markov chain phrase generator.


No, not forgetting it at all. In fact I was just pointing out his latest absurdity.


I don't think that AD is saying he expects it to run perpetually. I think he's saying that they should generate hydrogen as they run in order to help provide hydrogen fuel. Yes...he does come across as a bit nutty but he's a fuel cell evangelist. It's what he does.

Roger Pham

Well, even if the FC-powered ships are covered with solar PV panels, the electricity generated during the day time should be used to run the motor directly. There is no need for water electrolyzer on board the ship. Where is the source of excess energy to be used for H2 generation?

Roger Pham

Wind energy can be directly used for propulsion in the form of sails. Again, where is the source of excess enery?


It's so yesterday to ship products around the world based on production cost disparities. One continent is capable of producing all that is needed. In judicial terms it's called illegal competition. Granting full access to foreign companies would keep innovation alive.
As for the claim in the article, this is complete rubbish!
Aerosols cause light dispersion during sunset that causes additional sunlight resorption.


Aerosols cause light dispersion during sunset that causes additional sunlight resorption.

Even if this were true you're missing something.
First of all, even at sunset half of the light dispersed goes upwards so you're really getting less light that's only spread out over a longer time. Second, where does this "additional sunlight" come from? Well, the effects they're talking about are global while the sunset is local. The extra light you get for your sunset is being dispersed from the pre-sunset time from another part of the world so there's no net gain. Third, the earth is a sphere. This causes the light coming in at sunset to come in at a greater angle, through a thicker slice of the air, than it does during the rest of the day - and the rest of the day is a longer period of time than sunset. So, you get more light lost for a longer time than you would get back at during a few minutes of extra sunset.


What about mercury from bunker fuel?


What about mercury from bunker fuel?

Good question: Has anybody got any numbers?


I reviewed AD's comment about a fuel cell ship...I have to say I agree with the perpetual motion question. AD, what energy are you using to electrolysise hydrogen? If the engine is driving a generator, then it would be a net loss compared to just turning a prop shaft. If you're thinking about solar PV panels on the vessel, fine but then why not use them to drive the ship using E-assist or power crucial electrical onboard with that?

A fuel cell to POWER the ship's electric motors is a fine idea...and you could use solar to generate hydrogen while parked....but if you can generate that much hydrogen...think of how much of a waste that is compared to just driving the motors directly. You might be onto something if you are moored on the docks, connected to mains and generating fuel for your cell...I dunno. Could you clarify your vision?


AD is comic relief.  Ignore him.

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