Here at Ground Truth Trekking we’ve been hard at work on a new website… full announcement coming soon. Part of this has been doing a lot of reading on coal and other sources of fossil energy. One of the questions that particularly intrigued me involves how we might move to sustainable transportation. I’ve been wondering what we might replace oil based fuels for transportation with. Renewables as they are often discussed in the media focus around electricity generation, but the challenges and options there are a bit different than for transportation. So I thought I’d put together some of what I learned…

We’re headed toward some big changes in how we power transportation. Most people, including the US Dept. of Energy, think that high prices for oil will be back, and right now we run nearly all our transportation on oil. Also, global warming is largely caused by increases in CO2 from fossil fuels. So there is a widespread move to find fuels with smaller carbon footprints than conventional fuels.

Figure 1: Depending on what energy source is used for transportation, greenhouse gas emissions vary greatly. (Data mostly from EPA, 2007. Also Google Clean Energy 2030 Initiative and the DOE/EIA Annual Energy Outlook, 2009. To quantify these projections in the same way as the EPA, I assumed that the greenhouse gas emissions were proportional to percentage of generation from fossil fuels.)

Basically, it comes down to energy storage. Oil is old energy… stored in the fossilized remains of ancient organisms. There’s only so much of this old energy, and the high price volatility in the past few years is probably in part because we’re running out (or, more accurately, are nearing the peak of oil production).

And by using it we release carbon, as carbon dioxide, into the atmosphere that was otherwise stable beneath the earth—hence the greenhouse gas problem. So we’re looking for alternatives… Either another combustion fuel, or something else entirely.

Alternative Fossil fuels

Coal to Liquids

Oil prices on June 23, 2007.

Though oil may be running short, most people think coal, another fossil fuel, is abundant enough to meet our energy needs for a century or more (exception, extreme exception). In its native solid form it’s not very good for transportation. But liquid fuel similar to gasoline or diesel can be produced from coal through a refining process. Commonly called Coal to Liquids (CTL), large coal refineries would be built near mines to produce fuel. The problem with this is that between making and burning the fuel, over twice as much CO2 is produced (see Fig. 1).

Low Carbon Coal

Advocates of CTL suggest that some of the CO2 might be captured at the refinery, allowing it to be stored somehow, kept away from the atmosphere. But “low carbon coal” using carbon capture and sequestration (CCS) techniques like this have never been applied on a large enough scale for CTL, and are unlikely to be online in the near future.

Gas to Liquid

On the other side of the coin as far as alternative fossil fuels, its possible to take natural gas or gases from oil and fix them into a liquid form. These would extend our fuel supply only slightly, and release somewhat less CO2 to the atmosphere (Fig. 1).

Compressed Natural Gas

Natural gas might even be carried as-is, compressed and delivered to modified internal combustion engines. This provides the greatest benefit as far as CO2 reduction of any fossil fuel directly burned in an internal combustion engine (Fig. 1).


All of these options still directly use fossil fuels, and so will eventually need to be replaced by sustainable fuels. So fuels derived from living plants and algae are being explored as possible replacements for fossil fuels. These biofuels depend on either fermentation to produce alcohols (corn ethanol or cellulosic ethanol), or refining of photosynthesis-produced oils (biodiesel).

Corn Ethanol

Corn ethanol seems on the surface to have great potential. At least, that’s what the corn industry managed to convince the Bush administration of, leading to massive investment in corn ethanol. However corn ethanol has experienced a precipitous fall from grace. Environmental analysts found that the oil used to power the machinery, and to produce the pesticides and fertilizer to make the corn, was nearly as much as the fuel that was produced in the end (Fig. 1). This presents a problem both from an environmental perspective, and from an economic perspective. It means that price increases for petroleum derived fuels will translate straight into corn ethanol, so it’s tough for them to compete. Of course, it’s possible to grow corn with no fossil fuel help. Native Americans achieved this sustainably for many centuries, but they achieved that sustainability on a scale that has been dwarfed by modern industrial society.

Finally, if land use changes are factored in, corn ethanol really isn’t the way to reduce greenhouse gas emissions (Fig. 1). Especially if corn for ethanol displaces food production. This means that new land has to be brought into food production. As a result of carving new farmland out of the wilderness, CO2 is released that was previously held in the plants and soil that grew there. There are those who doubt this, but their reasoning is that we will see increased yields in the future, which requires increased use of fossil fuel based fertilizer and pesticides (known as the “green revolution“). Not to mention that stressing the food supply system at a time that may be the end of the pesticides and fertilizers that power the green revolution might be unwise…

Cellulosic Ethanol

We walked through hybrid cottonwood in northern Washington. Might these trees someday power cars?

Ok, so corn isn’t a good plant to ferment… what about using switch grass, hybrid cottonwood (poplar), or willow that can grow on poor farmland with little pesticides or fertilizer? This path has been less explored, and looks to be expensive, but may be one of the best as far as low CO2 impact.


Diesel has been produced by processing waste vegetable oil, or algae. In the case of algae derived biodiesel, biodiesel can be grown on land that is not suitable for food agriculture, but refining is easier, since instead of going through a fermentation process, the oils just need to be separated from the rest of the biomass.

Other possible fuels


Short of gathering it from other planets, hydrogen is not available as an energy source, but it may provide a way of storing energy from other sources for transport. Hydrogen can be made from fossil fuels, and then run through a fuel cell to produce electricity to run a motor. Or electricity can be used to split hydrogen out of water, possibly circumventing fossil fuels entirely (Fig. 1).


Probably the most immediate way to escape fossil energy sources for cars (but likely not for planes or container ships) is battery power. The battery technology is a limitation, but usable commuter vehicles now exist using batteries. If the energy for a vehicle can come from somewhere other than fossil fuels, then this becomes one of the most immediately sustainable options (see Fig. 1). This strategy is central to possible approaches to reducing US dependence on fossil fuels, such as the Google Clean Energy 2030 initiative.

Compressed air?

People are getting creative about ways to take the energy in the electric grid and put it in your car. Beyond batteries, and hydrogen split from water, there is work to use compressed air to power cars.

The Big Picture

The Road Warrior (Miller, 1981)

The challenge is not simply to find a way to change our current oil-derived fuels to something new. It is coming up with a new transportation infrastructure that in the short term can handle our immediate problems and that in the long term can be completely sustainable.

Part of this will be new ways of powering cars, trucks, plains, ships, trains… But it will include changes in how we use these modes of transportation. For example, right now, our military is in a particular bind… military jets and other vehicles consume vast amounts of fuel, and they need power and range that is not available for electric vehicles. Hence the military has been a big force behind CTL development. In a post-petroleum society, we might have trouble finding enough fuel to make war. Air transport has similar limitations for similar reasons. The personal vehicle fleet looks easier to re-configure… but an increase in the use of plug-in electric vehicles would be greatly facilitated by charging that occurred when electricity supply peaked (a “smart grid“). For transport of goods, it seems like it might be worthwhile to look at a modernized rail system. And for marine shipping, even futuristic sail might be an option. Regardless, with the end of easy and convenient petroleum fuels we’ll see big changes in the way our transportation works.

Further reading

Gas 2.0 blog
The Oil Drum
Google Clean Energy 2030 Initiative