Earth Day: How much do you know about climate change? Take our quiz.

A lot of people have opinions about climate change, but do they really know what they are talking about? Test your knowledge with this quiz.

2. On average, what percentage of the Earth's atmosphere by volume consists of carbon dioxide?

NASA/Reuters/File
A full moon appears through the blue glow of the Earth's atmosphere, in this photo taken aboard the Space Shuttle Discovery in 1999.

About 4 percent

About 0.4 percent

About 0.04 percent

About 0.004 percent

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