Historically, most cars have run on gasoline,
but that doesn’t have to be the case in the future:
other liquid fuels and electricity can also power cars.
So what are the differences between these options?
And which one’s best?
Gasoline is refined from crude oil,
a fossil fuel extracted from deep underground.
The energy in gasoline comes from a class of molecules called hydrocarbons.
There are hundreds of different hydrocarbons in crude oil,
and different ones are used to make gasoline and diesel—
which is why you can't use them interchangeably.
Fuels derived from crude oil are extremely energy dense,
bringing a lot of bang for your buck.
Unfortunately, they have many drawbacks.
Oil spills cause environmental damage and cost billions of dollars to clean up.
Air pollution from burning fossil fuels like these
kills 4.5 million people each year.
And transportation accounts for 16% of global greenhouse gas emissions,
almost half of which comes from passenger cars burning fossil fuels.
These emissions warm the planet and make weather more extreme.
In the U.S. alone, storms caused by climate change
caused $500 billion of damage in the last five years.
So while gas is efficient,
something so destructive can't be the best fuel.
The most common alternative is electricity.
Electric cars use a battery pack and electric motor
instead of the internal combustion engine found in gas-powered cars,
and must be charged at charging stations.
With the right power infrastructure, they can be as efficient as gas-powered cars.
If powered by electricity generated without fossil fuels,
they can avoid greenhouse gas emissions entirely.
They’re more expensive than gas-powered cars,
but the cost difference has been shrinking rapidly since 2010.
The other alternatives to gasoline are other liquid fuels.
Many of these can be shipped and stored using the same infrastructure as gasoline,
and used in the same cars.
They can also be carbon-neutral if they’re made using carbon dioxide
from the atmosphere—
meaning when we burn them, we release that same carbon dioxide back into the air,
and don't add to overall emissions.
One approach to carbon-neutral fuel is to capture carbon dioxide
from the atmosphere and combine its carbon with the hydrogen in water.
This creates hydrocarbons, the source of energy in fossil fuels—
but without any emissions if the fuels are made using clean electricity.
These fuels take up more space
than an energetically equivalent amount of gasoline—
an obstacle to using them in cars.
Another approach is to make carbon-neutral fuels from plants,
which sequester carbon from the air through photosynthesis.
But growing the plants also has to be carbon neutral—
which rules out many crops that require fertilizer,
a big contributor to greenhouse gas emissions.
So the next generation of these fuels must be made from either plant waste
or plants that don't require fertilizer to grow.
Biofuels can be about as efficient as gasoline, though not all are.
For a fuel to be the best option, people have to be able to afford it.
Unfortunately, the high upfront costs of implementing new technologies
and heavy subsidies for the producers of fossil fuels,
mean that almost every green technology
is more expensive than its fossil-fuel-based cousin.
This cost difference is known as a green premium.
Governments have already started subsidizing electric vehicles
to help make up the difference.
In some places, depending on the costs of electricity and gas,
electric cars can already be cheaper overall,
despite the higher cost of the car.
The other alternatives are trickier, for now—
zero-carbon liquid fuels can be double the price of gasoline or more.
Innovators are doing everything they can to bring green premiums down,
because in the end, the best fuel will be both affordable for consumers
and sustainable for our planet.