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Study concludes a shift from gasoline to diesel engines is consistent with long-term climate mitigation efforts

Global-mean temperature change caused by car exhaust emitted from gasoline and diesel engines specified in the previous and upcoming European vehicle emission standards (EURO 3, 4, 5, and 6). The results are based on one-year pulse emissions in year zero, which would be emitted by an idealized 1000 km drive. Credit: ACS, Tanaka et al. Click to enlarge.

A shift from gasoline to diesel engines following previous and upcoming European emission standards is consistent with long-term climate mitigation efforts, according to a new analysis by researchers from CICERO (Center for International Climate and Environmental Research, Norway), the University of Oslo and ETH Zurich. Their paper is published in the ACS journal Environmental Science & Technology.

Passenger transport affects climate through various mechanisms involving both long-lived—i.e. CO2—and short-lived—e.g., black carbon, BC—climate forcers. Diesel cars generally emit less CO2 than gasoline cars, hence CO2 emission taxes for vehicle registrations and fuels have been shown to enhance the consumer preference for diesel cars over gasoline cars, the authors note. However, previous studies have shown more prolonged warming due to diesel cars under various conditions.

The difference between their current study and previous efforts, the authors say, can be explained mainly by the combination of the factors such as underlying emissions (pulse or sustained), carbon cycle model, BC efficacy, and atmospheric chemistry processes considered.

A climate mitigation policy that focuses on CO2 emissions supports an increase in the fraction of diesel cars because passenger cars equipped with diesel engines emit on average 15% less CO2 per kilometer than vehicles with gasoline engines with a similar power output. After the UK had begun taxing vehicles according to CO2 emissions, the share of registered new diesel cars increased from 26% in 2002 to 38% in 2005.

However, it is not clear whether the shift from gasoline to diesel cars, which is encouraged by CO2 taxes for vehicle registrations and fuels, would be effective as originally intended as a climate mitigation measure, given a number of non-CO2 components emitted together. Many of them have indirect climate effects through chemical reactions or by changing the planetary albedo. NOx, CO, and HC emissions lead to a production of O3 (“short-term O3 formation”) as well as a change in the levels of the main oxidant in the atmosphere, the OH radical. NOx emissions and the produced O3 enhance the production of OH, while CO and HC emissions reduce OH levels. The change in the OH concentration affects the lifetime of CH4, which has a longer-term impact on the O3 production (“primary mode”). BC and OC absorbs and reflects sunlight, respectively (direct effect) and BC changes the albedo of snow/ice (albedo effect). BC and OC may also change cloud properties through the indirect and semi-direct effects. Furthermore, aerosol abundances are influenced by OH through gas-aerosol interactions.

—Tanaka et al.

To analyze whether a policy that encourages diesel cars is consistent with a long-term climate goal to cap global warming, the team calculated the global-mean temperature change that would be caused by the use of gasoline and diesel passenger cars under the previous and upcoming emission standards in Europe (EURO 3, 4, 5, and 6).

For their study, they used a simple climate and carbon cycle model combined with aggregated parametrizations of atmospheric chemistry processes (explicitly including the short-term O3 response and the primary mode perturbation). To reduce the complexity of the task, they assumed gasoline and diesel cars exactly followed the emission standards and had a similar power output.

Nor did the study consider the impact of a fleet of aging models adhering to different emission standards, or any technology options other than standard gasoline and diesel—i.e., no shift to hybrids, plug-in hybrids, battery-electric vehicles or fuel cell vehicles. The study also focused on climate impacts alone, without comparing with the adverse health impact caused by the air pollution.

Their analysis used one-year pulse emissions as well as sustained emissions over an average car’s lifetime (15 years), and adopted the IPCC Impulse Response Function (IRF) designed to represent carbon cycle processes on various time scales.

Among their findings were:

  • The newer emission standards generally lead to a smaller net warming.

  • Long-term warming from diesel engines is smaller relative to that from gasoline engines for any emission standard because only the CO2 emissions count in the long run. After 100 years, the warming from diesel cars is about 20.4% smaller than that from gasoline cars in the case of EURO 3; and 17.7% in EURO 4; 15.4% in EURO 5; and 10.2% lower in EURO 6.

  • The initial temperature response is drastically different between the early emission standards (Euro 3 and 4) and the later standards (Euro 5 and 6). The magnitude of the warming caused by diesel cars under EURO 3 and 4 exceeds that by gasoline cars during the early phase of operation by up to a factor of 2.0 and 2.5, respectively due to the large influence from the short-lived components O3 and BC.

  • The crossover points, beyond which diesel cars cause less warming than gasoline cars, occur closer to the emission year as the advanced emissions standards set in 5 years, 5 years, 3 years, and 2 years for EURO 3, 4, 5, and 6, respectively, because of the more stringent caps for short-lived components (O3 precursors and BC) in the newer emission standards. In the cases of EURO 5 and 6, BC emissions from diesel cars cause only a small warming.

  • During the first 10 years of contributions from the non-CO2 components are significant, causing both warming and cooling. The short-term impacts (warming and cooling) are substantially larger for diesel engines due to the higher emissions of NOx (leading to short-term O3 formation) and carbonaceous particles.

  • The climate response due to the short-term increase in the O3 concentration is stronger for diesel engines than for gasoline engines. This short-term O3 effect explains 45% of the total warming at the end of the first year.

  • The only significant effect of carbonaceous particles is the BC emissions from diesel engines. At the end of the first year, the contribution from BC is as large as 43% of the total warming, but during the first decade after the emissions it decreases to 10%. In the long term (20 years or more), the contribution from BC is very small (less than 2%).

  • For diesel cars, the primary mode effect reduces the warming by up to 22% (10 years after the emissions). For gasoline cars, the lower ratio of NOx to CO + HC emissions leads to a reduction in the OH concentration and thus an increase in the CH4 concentration, resulting in a small temperature increase (less than 5% of the net warming).

When interpreting our conclusion that CO2 taxes are in line with efforts to reduce our impact on the climate, one should keep in mind that in general, considering relevant non-CO2 components in addition to CO2 is essential in designing climate-related policy instruments because non-CO2 components play an important role in characterizing the short- to middle-term climate response—it is not unlikely that other instruments in different sectors or cases lead to a variety of climatic outcomes including those incompatible with efforts to reduce our impact on the climate. Furthermore, policy makers would need additional considerations beyond what we addressed here.

For example, the rebound effect may significantly influence our results. It has been argued that consumers use a part of the money saved through opting for a diesel engine for upgrading to a larger engine. The rebound effect may also work through increased driven mileage (in addition to larger engines). This implies that the difference between the CO2 emissions from gasoline engines and those from diesel engines could be effectively smaller than what we obtained, reducing further the difference between the long-term climate effects expected for gasoline-fueled vehicles and that for diesel-fueled vehicles.

—Tanaka et al.


  • Katsumasa Tanaka, Terje Berntsen, Jan S. Fuglestvedt, and Kristin Rypdal (2012) Climate Effects of Emission Standards: The Case for Gasoline and Diesel Cars. Environmental Science & Technology doi: 10.1021/es204190w



I have been advocating for a long time for the feds to concentrate on dispersed Algae production. We need to develop an infrastructure to produce and supply diesel across the United States.

The end point dispensing infrastructure already exists. No other form of transportation energy distribution would be as easy, and quick, to establish.


And you can count on advocating for a while longer, if you care to.


GTL diesel, algae diesel, bio diesel, CNG/LNG can all help reduce imported oil. Big rigs consume more than 10,000 gallons each per year and there are millions of them. If we could just get big rig delivery to super markets on LNG we would be ahead.


If we could get big rigs and railroads running on LNG, the basic transport infrastructure of the USA would be immune to disruptions in the petroleum supply (until the NG supply went down again, but that will take time).

That's a good move for both national security and balance of trade (USA's ULSD is a hot item in international commerce).



Trains have plenty of room for the lower density CNG, just add a tanker car to the train


Anywhere you have a fixed route and duration, it may be possible to use LNG, whether it is big rigs or railroads. However, the vehicle has to be converted, it requires change and that is where the reluctance is.

When you can put synthetic fuels into the vehicle just like you do refined fuels, there is no change required. This does not require change to the big rig tractor nor the railroad engine. People are much more receptive to this rather than changing what they have at increased expense.

You can explain efficiency all you want, but if it costs $50,000 per big rig and $500,000 per railroad engine and another $5 million for LNG fueling depots they start to calculate what it will cost and who will pay for it.


E-P...the only road block to what you're rightly saying is Big Oil.

SJC...with current very low NG price, the recovery time could be less than 5 years without subsidies in most cases and less than two years with Volt type weighted subsidy.

From an environmental, economical, local employment and trade deficit point of view, heavy long haul trucks and locomotives may be the best place to start.


Let's say we have 4 million big rigs and it costs $50,000 per truck to convert them to LNG, that does not include the LNG facilities to fuel them.

This would be an expenditure of $200 billion dollars to convert all the trucks, which would be enough money to create 200 GTL plants producing one million gallons of synthetic fuel per day each.

Since the synthetic fuel plants could provide fuel to all trucks and not just big rigs, it makes sense from a societal expense to build the fuel plants that can operate for 50 years or more.

Those same plants, with some modification, could produce gasoline and jet fuel while using coal and/or biomass as well as natural gas.

Do you raise the bridge or lower the river? Do you create fuels that will run in existing vehicles by the millions or do you convert millions of vehicles to use the fuel you want to provide?


If the rig burns 15,000 gal/yr of diesel or NG equivalent and LNG goes for $2/gde, a conversion would save about $30,000/yr in fuel cost.  Even if a conversion costs $50,000, it would pay for itself in 20 months out of the 60-month major overhaul interval.  Those rigs would never go back to diesel, and new ones would ship with LNG systems.

Who'd put money into a plant for GTL diesel (a 50-year investment) when the market can vanish in 5 years?  The same question applies to GTL gasoline; all major manufacturers are offering dual-fuel pickup trucks.

The Shell/Sasol plant being talked about for Louisiana would be about $10 billion.  I suspect it will never be built.


I don't think the market for liquid fuels will vanish in 5 years and neither do experts that have looked at it. I have seen slide sets from industry experts projecting out the need for liquid fuels in large quantities until the year 2100.

They also showed that about now synthetic fuels would take a larger share of the market year after year from here on out. You can say it should not happen, that we should convert all trucks to LNG, that all of us should be driving EVs, that all cars will be replaced by EVs and all trucks will be replaced by LNG, but others don't share that belief.



Commercial trucks see near constant use. As a result their average lifespan is only 5 years. Even before they get replaced they'll get overhauled several times. The average rate for major overhauls is once every 4000-5000 hours of operation.
I don't know what the numbers are for trains but they'd also have to have a routine maintainance/overhaul schedule. In other words, there is plenty of opportunity for converting them to NG and major cost savings to be had if they do.


There may be plenty of opportunities, but will they take those opportunities. It costs them money to overhaul and now it will cost them more to change to LNG.

The same argument can be applied here, if natural gas prices may not stay low forever, the whole calculation changes over time. If I can put biomass or coal into my gasification plant and still make fuels, I have an option.

I can not put biomass nor coal into the fuel tank of my truck nor locomotive engine. The days of coal powered locomotives has long passed and that is good. The amount of smoke that was belched while coming into city train stations was horrible.


Actually, the costs of overhauls should be lower with a NG conversion. Many users of gaseous fuels have reported positive benefits relative to engine wear including extended oil change intervals and extended time between overhauls. This is primarily the result of the cleaner burning characteristics of LPG and natural gas compared to diesel fuel.

I can not put biomass nor coal into the fuel tank of my truck
Animal poop + digester + cleanup + dual-fuel pickup truck.

Converting trucks and buses to CNG, big rigs and locomotives to LNG sounds good, but I would not count on that happening in the big way real soon.

A high probability of success says that we go with moves that will actually happen in a big way in a short time frame. A robust plan says that we have several plans, so if conditions change, we have options.


A locomotive that achieves 400 ton-miles per gallon [1] and pulls 5,000 tons of freight at 50 MPH 16 hours per day burns 10,000 gallons of fuel PER DAY.  That's more in 2 days than the typical big rig burns in a year.  If the fuel cost advantage is as little as 50%, LNG conversions will pay off very rapidly for that segment.  Carbureted NG would require even fewer changes and could shift 80% of the fuel to NG.

Electrified rail beats NG fuel.  The greater power of the electric locomotives moves more stuff faster, and the higher efficiency of stationary powerplants and their more varied energy supplies inherently diversifies the system and adds energy security.

Road-borne freight and personal vehicles are another matter, but between CNG/LNG, dual-mode tractor-trailers, PHEVs and the like there are options out there.  Some can be pursued in the market (PHEV, CNG), some require a lesser (LNG) or greater (dual-mode) buy-in for infrastructure.  We need to invest in demonstration projects and see what's ready for prime-time.

[1] CSX claims 423 ton-miles per gallon.


It could be easier and more profitable to start with NG locomotives on selected routes because they can carry more fuel on each train, can travel a very long way without the need for an NG refueling station, each locomotive burn much more fuel than a single heavy truck, plenty of room for the modification etc.

Mr Red Rose120

this is nice post and having a good status in the market, it is also called the house of knowledge,

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