In this episode, we’re answering a question from listener Katelynn: “Why is car exhaust bad for the planet?”

Our planet NEEDS some carbon dioxide, but cars are pumping more into the atmosphere than our carbon cycle can handle. We’ll explore what all this carbon means for our planet.

And we talk to Anne Co, a scientist who is working to change how we fuel our cars, so we can cut back on all this carbon dioxide. She explains how fuel cells and batteries work to power electric cars. Anne’s vision for the future of cars can be summed up in one word: electric.

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Internal combustion engines create a reaction between gas and the air. One of the byproducts of this reaction is energy, which powers the car.

But there are less pleasant substances that are also created during this reaction — like hydrocarbons, nitrogen oxides and carbon monoxide. These substances are harmful to the environment.

However, there’s a part in cars designed to reduce these three substances called the catalytic converter. It takes these harmful pollutants and transforms them into less harmful emissions.

But even if your engine is working perfectly efficiently, and the catalytic converter is doing a perfect job, the basic combustion reaction creates a byproduct that cannot be avoided: carbon dioxide, also known as CO2.

Carbon dioxide is a colorless gas with no smell made from carbon and oxygen and by itself it’s not a bad thing. In fact, we make carbon dioxide all the time when we breathe. Plants then take it in and use it during photosynthesis. That process, in turn, makes oxygen for us to breathe.

This is all part of something called the carbon cycle. Animals, including humans, exchange carbon dioxide with plants. The atmosphere exchanges carbon dioxide with the ocean. Carbon really gets around. It’s natural!

And it’s carbon dioxide in the atmosphere that makes life on earth possible. Light comes from the sun and hits the earth. Stuff on the earth then reflects that energy back into the air as heat. Lots of molecules in the atmosphere like oxygen and nitrogen just let that heat pass right through back out to space

But carbon dioxide is different. It traps that heat, acting like a kind of blanket and that’s a good thing because life on earth needs that heat to survive. Without some carbon dioxide the planet would be an icy, frozen mess.

But too much CO2 and things would get super hot, which is also not great for life.

When carbon dioxide makes its way to the atmosphere it takes a while for it to leave, and lately humans have started pumping more carbon dioxide into the atmosphere than the carbon cycle can handle on its own. It’s not just from cars but also power plants and factories, which also burn carbon-based fuels and release CO2 into the atmosphere.

But how do we know this extra carbon dioxide is coming from burning gas and other fossil fuels — and there’s just not more people breathing?

That’s because the carbon dioxide produced by burning fuel is slightly lighter than carbon dioxide found naturally in the atmosphere.

The amount of carbon dioxide produced by burning carbon-based fuel has been on the rise since the 1850s thanks to the industrial revolution, which gave rise to factories.

And remember how plants use CO2 during photosynthesis? Well, trees take in a lot of CO2, but some of our biggest trees, like in the tropical rainforests, get chopped down or cleared for other purposes. Without those giant forests taking up the CO2, we are left with a lot more in the atmosphere.

Even though CO2 is only a small part of the atmosphere, this increase has an impact. It means more and more heat is getting trapped in the atmosphere. That’s making average temperatures here on on earth slowly rise, leading to changes in our climate.

But reducing the amount of carbon dioxide we put into the atmosphere would help fight this change.

Anne Co is a scientist working to change how we fuel our cars by making electric cars more affordable and convenient. Listen to the episode to learn more.

Brains On! is an award-winning audio show for kids and families from American Public Media.