Carbon dioxide gets a lot of grief these days.

It’s the main cause of the global warming that’s already damaging coral reefs, ice caps, and coastlines.

But for eons, life survived on Earth because natural processes kept CO2 levels within limits, preventing the planet from getting either too cold or too hot.

So, if we want to keep earth from warming more than a few degrees, we probably need to supercharge those natural processes, in a hurry.

Or maybe even invent some new methods to suck carbon out of the sky at an even bigger scale The question is, can we capture all that carbon before earth becomes too hot for us?

Hey guys, I’m Joe.

Behold the mighty carbon cycle!

Life’s most important element is never created or destroyed, it’s only moved around.

Natural sources of carbon like volcanoes and decomposing trees add carbon dioxide to the sky, heating up the Earth, while natural carbon sinks like oceans, growing forests, and weathering rocks remove carbon from the atmosphere, cooling off the planet.

These carbon sinks may offer clues on how we can limit global warming.

Here’s one idea: add tiny amounts of iron to certain parts of the ocean to jumpstart massive algae blooms that suck up a bunch of carbon.

Hopefully, they die and sink to the ocean floor, locking the carbon away, just like the carbon-rich algae whose skeletons formed the White Cliffs of Dover millions of years ago.

But when we’ve actually tried this, it turns out other microorganisms end up eating the dead algae and breathing out that CO2, which then re-enters the atmosphere instead of being locked away.

Ok, so why not just plant more trees?

They suck carbon out of the air and turn it into trunks, leaves, roots, stuff like that.

But we've been taking carbon that got buried over millions of years, and putting it back in the air basically all at once, and there’s just not enough room to plant all the trees it would take to suck all that carbon back out of the air, especially because we currently use a lot of land for other things, like growing food.

Ok, supercharging natural carbon sinks like this won’t be enough to keep earth from overheating.

What if we also shove carbon underground ourselves?

CO2 is pretty unreactive, and there’s only 4 molecules of it for every ten thousand molecules of air, so it’s hard to grab and concentrate it.

Luckily, plants are amazing at it - it's pretty much what they do.

If we plant a lot of fast-growing grasses, they’ll turn a lot of CO2 into living tissue.

Then we can burn them to turn that living carbon back into a concentrated stream of carbon dioxide.

Finally we grab that CO2 using carbon-scrubbing devices and inject it deep underground, permanently removing it from the atmosphere.

It’s a promising approach.

But paying farmers to grow grasses could incentivize them to expand their fields into native ecosystems that already hold a bunch of carbon in plants and soil.

So converting those ecosystems to grasslands would release massive amounts of carbon, when putting carbon underground is the entire point.

That’s not good.

You know what’s good?

Spaceships!

They use chemical devices to remove excess carbon dioxide from their cabins and spacesuits.

If we employ a similar strategy, say for uh, THE ENTIRE ATMOSPHERE we can take CO2 right out of the sky.

Scientists call it Direct Air Capture, and it involves strong chemicals like lye that can snare carbon dioxide.

This method takes carbon out of the atmosphere, but we can also prevent the carbon from going into the atmosphere, by grabbing it where it’s most concentrated, in smokestacks.

Remember those scrubber things we can use to capture carbon after we burn plants?

If we place them in power plants or refineries we can remove pollution before it enters the atmosphere - and then, yes, shove it underground.

These two methods–scrubbers and Direct Air Capture– have worked in small scale experiments, but most large-scale attempts to grab and store CO2 underground have failed economically.

These technologies could get the job done, in principle, but right now, it doesn’t cost companies anything to put CO2 into the sky, so there’s pretty much no financial incentive for companies to avoid it, or to take it out.

But as a civilization we do pay a cost if we can’t get carbon out of the atmosphere: runaway climate change.

So to keep Earth from dangerous warming, we need to clean up the skies.

The most direct way to do that is to stop putting more carbon in the air, by transitioning away from coal and gas and by using energy more efficiently.

But here's a tough fact to face: there's already so much carbon dioxide in the air that keeping climate change under control will probably require us to deploy carbon sucking methods on a massive scale.