But examining the top proposed fixes shows how difficult any transformation would be. Improvements must be substantial, or dramatic increases in the number of cars and in oil sands output will overwhelm any gains in carbon reduction.

Most discussion about greener cars focuses on engine improvements. But advances are happening in other areas. Weight loss through materials such as aluminum and carbon fibre; aerodynamic designs; accessories powered by electronics instead of belts and pulleys; and continuously variable transmissions are available now and are relatively inexpensive.

These developments and modifications to conventional engines—such as direct injection and variable valve timing—each produce small fuel-economy gains that add up and are the main route for carmakers to reach the tougher emission standards taking effect in 2016.

A new technology may be a bigger leap. Homogeneous charge compression ignition, or hcci, might come through with up to 15 per cent less fuel consumption. It’s a cleaner, more complete burn that doesn’t use spark plugs. As with conventional engines, hcci mixes gasoline and air before injecting the mixture into the combustion chamber. The difference with hcci is that that the piston compresses the fuel as it rises up the cylinder, raising the fuel’s temperature until it’s hot enough to ignite.

As a result, hcci is much harder to control than spark ignition, and requires extremely precise valve timing and control of the air/gasoline mix and its temperature— not yet accomplished.

It also functions poorly at low speeds and under heavy load. Some suggest a dual system, with spark ignition part of the time, but that would add complexity and cost.

With the number of cars soaring worldwide, these changes, or even widespread adoption of conventional hybrids, won’t solve the greenhouse gas problem.

Plug-in hybrids could be better. Various manufacturers are unveiling models said to go 15 to 60 kilometres after an overnight recharge—enough mileage for most routine driving on battery power alone. Actual fuel consumption and emissions, though, will depend on how many trips stay within that range.

All-electric cars could be game-changers. Cost is a major impediment, as are current lithium ion batteries, since most are limited to less than 200 kilometres between charges.

Researchers are exploring lithium air, which employs air instead of a heavy metal to create the reaction that generates electricity. Theoretically, the result is a much lighter, more efficient battery with a range of up to 800 kilometres. Again, cost and degree of technical difficulty remain high— particularly since lithium can explode when exposed to air—and it’s at least a decade or two from commercial use.

Battery-powered cars will only reduce climate change if their electricity comes from renewable sources. On the other hand, computer-controlled systems are being devised to let utilities use plugged-in cars as electricity storage facilities, drawing power from them at times of peak demand. However, that process is slow and shortens battery life, so it’s likely “to be the exception rather than the rule,” says Dan Guatto of Burlington Hydro, which is testing a battery-powered Ford Escape converted by Vancouver-based Rapid Electric Vehicles.

Although the oil sands projects have environmental impacts beyond greenhouse gas emissions, shrinking their carbon footprint is crucial.

Most of tar sands’ heavy primary oil, or bitumen, now originates in open-pit mines, but an increasing proportion is extracted in situ—forced up through wells from underground. A report from the Calgarybased Canadian Energy Research Institute (ceri), to be published this fall, concludes each mining process requires a different solution.

Per barrel of oil recovered, mining emits much less greenhouse gas than in situ, but its vast scale makes the total amount huge. As with cars, a series of small improvements has reduced its impact, but major change is required.