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Report Finds that GHG Reductions of More Than 50% from Projected BAU Levels by 2050 from Aviation and Marine Transportation Sectors Are Possible

Global GHG mitigation potential from aviation and marine transportation. Source: McCollum et al. Click to enlarge.

Reductions of more than 50% below projected business-as-usual greenhouse gas emission levels by 2050 from global aviation and more than 60% for global marine shipping are possible, according to a recent report published by the Pew Center on Global Climate Change and written by David McCollum and Gregory Gould, both from UC Davis and the Institute of Transportation Studies there; and David Greene, Oak Ridge National Laboratory.

The report, “Aviation and Marine Transportation: GHG Mitigation Potential and Challenges” presents an introduction to aviation and marine transportation and a discussion of the determinants of GHG emissions from transportation; gives overview of current emissions and trends and growth projections; explains the technological mitigation options and potential GHG emission reductions; and discusses policy options at both the domestic and international level to achieve deep and durable reductions in emissions.

Aviation and marine transportation combined are responsible for approximately 5% of total GHG emissions in the United States and 3% globally and are among the fastest growing modes in the transportation sector.

Under business-as-usual forecasts, CO2 emissions from global aviation are estimated to grow 3.1% per year over the next 40 years, resulting in a 300% increase in emissions by 2050. International marine transportation emissions are estimated to grow by 1 to 2% per year, increasing by at least 50% over 2007 levels by 2050. Controlling the growth in aviation and marine transportation GHG emissions will be an important part of reducing emissions from the transportation sector.

A range of near-, medium- and long-term mitigation options are available to slow the growth of energy consumption and GHG emissions from aviation and marine shipping. For the near- to medium-term (to 2025), improvements in operational efficiency (e.g., advanced navigation and air traffic management systems for aviation and slower marine vessel speeds) have the potential to reduce GHG emissions below BAU projections by about 5% for aviation and up to 27% for marine shipping in the near to medium term (to 2025).

For the long-term (by 2050) advanced propulsion systems and new airframe designs could further reduce aviation CO2 emissions by up to 35% below BAU projections. For marine transport, larger ships, new combined cycle or diesel-electric engines, and optimized hull and propeller designs could provide an additional 17% reduction in emissions below BAU projections by 2050.

Reducing the carbon intensity of the energy sources used in aviation and marine transportation, by transitioning to alternative fuels and power sources, also could reduce GHG emissions over the medium to long term, although the level of potential reductions is uncertain. Aircraft and marine vessels could be powered by low-carbon biofuels or perhaps even hydrogen. While numerous technical challenges still exist, the main challenge to the use of alternative fuels will be the ability of aviation and shipping to compete with other transportation subsectors for a potentially limited supply of low-carbon biofuels. This could particularly be an issue with marine shipping, where the industry currently consumes the lowest-cost fuels available, namely residual fuel oil. Marine vessels could also benefit from switching to lower-carbon, conventional fossil fuels (e.g., liquefied natural gas and marine diesel oil) or to other renewable energy sources, such as wind or solar power.

—McCollum et al.

Looking beyond technical measures, the authors note that while reducing the demand for aviation and shipping could achieve GHG reductions, the potential impacts are probably limited.

The challenge for these subsectors is that there are few suitable alternatives for the services provided by aviation and marine shipping. High speed rail could replace some passenger air travel, but currently there are few alternatives to marine shipping. Marine shipping is already the most efficient, lowest-cost form of transportation, aside from pipelines, which compete with shipping in just a few markets. With only modest cost increases likely to be achievable through policy intervention, and a limited number of alternatives, a large reduction in demand compared to BAU seems unlikely from these subsectors.

—McCollum et al.

For these reductions to be realized, however, international and domestic policy intervention is required, the authors write. Developing an effective path forward that facilitates the adoption of meaningful policies remains both a challenge and an opportunity.



richard schumacher

- Completely artificial fuels made with non-fossil energy and carbon content derived entirely from atmospheric CO2 make no net contribution to global warming and have none of the production restrictions of biofuels. Blend in 30% of these and instantly you get a net reduction of 30% in fossil carbon emissions.

- Use nuclear powered ships with a completely sealed power unit (the crew have no access to it). Swap the core out every year or two to refuel. If we're concerned about security, use thorium instead of uranium fuel and/or put a detail of Marines on each ship.

Start pricing all of the external costs of global warming into fossil fuels and both of these options become economical well before the year 2050. We're going to have to do it eventually anyway; the sooner we start the more benefit we'll get from it.


The Pew Center and its contractors would do well to begin the inevitable transition from "climate" language to "energy" language. The reason becomes clearer every day. There is no correlation between atmospheric CO2 and global warming. But we DO need to transition away from reliance on fossil fuels.

The report should emphasize the need for accelerated alternatives to residual fuel oil on the basis of two factors:

Bunker oil and jet fuel produce real pollutants having nothing to do with "CO2 emissions." They are dirty fossils that cause conflict and inhibit conservation.

The overall consumption/reduction of fossils should be the active measure, NOT GHG emissions.

What the authors fail to perceive is the need for national and international energy policy to adopt more alternatives NOT to save the planet from global warming - but from real pollutants and particulates and more importantly, the conflict results from fossil fuel exploitation.


I think sulleny said it well.

On richard's post;
Our abandonment of nuclear power (and allowing it to be litigated out of reach) was, IMO more short sighted, more costly and far reaching than our love affair with large vehicles, but;
How does just the ability to do something ("non-fossil energy and carbon content derived entirely from atmospheric CO2 ") make it economical?

If we (the US) "Start pricing all of the external costs of global warming into fossil fuels" maybe it all becomes un-economical ; compared to the rest of the world.
If the whole world does it, regardless of cost, then it does get done - but still at some cost, and that cost could be severe.

They say ”Aviation and marine transportation combined are responsible for approximately 5% of total GHG emissions in the US and 3% globally.”

I expect that the cost of fuel will limit the “3.1% per year” growth (for air and sea) below their BAU forecast of “300% increase in emissions by 2050” .

Draconian, unilateral, "California like" penalties by the US should be avoided.


There appear to be a LOT of people posting about nuclear-to-hydrocarbons lately.  I have to wonder if this is an astroturf campaign.

There was a white paper on a proposal called "Green Freedom" to do just that.  I analyzed it; it's bunk.  The idea is more expensive than BEVs, far less efficient, reduces carbon emissions far less than other possibilities, and appears to be aimed at maintaining a market for oil (because the entire vehicle market would still use gasoline).


I think direct nuclear-to-hydrocarbons might be as similarly impractical (or worse) as nuclear-to-hydrogen in many ways.

The only caveat might be for the military and aircraft (maybe); but not for autos.



This is a plot of temperature vs CO2. The correlation is pretty obvious.

And it gets even better: there is causal link between temperature and atmospheric CO2, i.e. a mechanism to explain the correlation.

If you try a bit harder, you too can learn the difference between noise and signal.

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