As I was perusing my UC Davis alumni magazine last night I ran across a short article mentioning a new book from a professor, Dan Sperling, who directs Davis's well-regarded Institute of Transportation Studies. I know him slightly from his participation as in invited expert in a scenario workshop many years ago, so this caught my eye. His book, which I haven't read yet, examines the impact and implications of the rapidly growing global vehicle population, which he sees reaching the two billion mark within the next 20 years. In the article he suggested that this would require an entirely new transportation energy mix, made up of hydrogen, electricity, and advanced biofuels. That certainly fit my own long-standing expectations, as well. However, it occurred to me to wonder just how far we might be able to stretch the transportation fuels we get from oil, and just how far short they would fall as the global car-park expands. To my surprise, it doesn't require very aggressive assumptions concerning improvements in fuel economy, reductions in vehicle miles traveled, and additional oil supplies to cover the needs of a significantly larger number of cars in the world.
The starting point for such an analysis is current oil supplies and the way we process them. Global oil output in 2008 reached 86.5 million barrels per day (MBD), including crude oil, natural gas liquids, and the volumetric gain that occurs when you run them through a modern refinery. Roughly 60% of that input is currently turned into gasoline, diesel and jet fuel. Improvements in refining technology should make it possible to push that fraction to perhaps 70%, at the expense of heavy fuel oil displaced from power generation and shipping. So even if global oil output plateaued at only 90 MBD, a scenario that would probably seem optimistic to the adherents of Peak Oil and pessimistic to some industry experts, it could still yield 63 MBD of liquid transportation fuels. Set aside 7 MBD of that for jet fuel and kerosene and another 26 MBD for trucking and home heating oil, and we're left with 30 MBD of gasoline and diesel for passenger cars. That's roughly 25% more than current global consumption in light-duty vehicles, including the couple of MBD of diesel fuel that power Europe's popular diesel cars.
That doesn't seem to get us nearly far enough, until we consider that in the near future, cars will become much more efficient than they have been, particularly in the US, where an improvement from the current notional average of 25 mpg to the required 35.5 should eventually reduce average fuel consumption per mile by 30%. If the recent reversal in annual vehicle miles traveled persists after the recession ends, that would compound future fuel savings. When we consider that new cars in Europe currently average about 35 mpg and are required to reach approximately 43 mpg by 2015, based on a standard of 130 grams of CO2 emitted per kilometer, and that China has also introduced stricter fuel economy standards, it's not hard to imagine the average world car getting 40 mpg by 2020. That doesn't even require the majority of cars to be hybrids, let alone plug-in hybrids. If that average car drove 9,000 miles per year, it would consume 225 gallons of fuel annually. Following this back-of-the-envelope calculation to its conclusion, our 30 MBD of petroleum-based fuel for light-duty vehicles would be sufficient to cover Dr. Sperling's 2 billion cars with a little bit left over.
I'm not for a moment suggesting that this is the likeliest scenario, or that it means we don't need any of the advanced biofuels or electric vehicle technology currently under development. As I've pointed out frequently, fleet turnover in the developed world has slowed, thanks to the recession, and we can expect a long "tail" of older vehicles to persist for some time. However, the results of this simple exercise surprised me; I had expected the final number of cars that could be supplied by oil to be much lower. So while our transportation energy mix in the next couple of decades is still likely to include a much greater variety of fuels and an increasing penetration of electricity, we should not lose sight of the potential for realistically-achievable fuel economy improvements and non-efficiency conservation--driving personal cars less and relying more on mass transit and electronic trip substitution--to be the most important "transition fuel" in our arsenal, as we reduce our present reliance on oil, in order to tackle energy security and climate change.