NOVA

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Narrator

Cooling the planet means first stopping more CO2 from entering the atmosphere, and then finding ways to remove it. But just how much CO2 are we talking about? Imagine you filled the National Mall all the way from the Lincoln Memorial to the Capitol steps with coal... (dramatic music) (coal rattling) and you piled it up all the way to the top of the Washington Monument 10 times... that would be a gigaton of coal. Giga means billion, so that's a billion tons. Now, we actually burn 10 times that much carbon every year. People actually go dig that stuff up out of the ground, 10 billion tons of it, and set it on fire in power plants, in engines, in factories, all over the world. (dramatic music) And then, because that carbon has reacted with oxygen, 10 gigatons of carbon is burned, but it creates 37 gigatons of CO2. -

Narrator

At our current rate, that's just one year of CO2 emissions. (dramatic music) To blunt the impacts of heating the planet, we need to shrink that number to zero. But there's another problem. The gigatons that came before. The single most important fact about climate change is that the carbon dioxide that we emit into the atmosphere stays there for thousands of years. -

Narrator

Year after year, we live with the carbon dioxide we've added over time, nearly 1,000 metric gigatons since the Industrial Revolution began. -

Jane Long

Almost everything we emit stays there. And it's staying there until you do something about taking it out. (coal rattling)