Scientists first started thinking about climate change when they noticed an unexpected trend: It’s getting hotter outside. In fact, the 10 hottest years ever recorded have all been since 2005 (source).

Researchers began connecting the dots:

• Hotter air holds more moisture, leading to stronger storms.
• Hotter oceans cause melting of ice caps and higher sea levels.
• Hotter temperatures cause subtle changes in wind and weather patterns that have major ripple effects.

But if hotter temperatures are causing the dangerous weather, what’s causing the hotter temperatures?

Scientists considered various causes, like sun flares and volcanic eruptions, but in the end they found one clear answer: carbon dioxide (a type of gas). The amount of carbon dioxide in the atmosphere has been extremely closely tied to how hot the Earth has been for millions of years in the past, and, just like you might have guessed, the amount of carbon dioxide in the atmosphere has shot way up in the last 150 years!

So scientists are pretty confident that the amount of carbon dioxide in the air is correlated with how hot the Earth is. But is carbon dioxide causing the hotter temperatures? How would that even work?

Bonus Video

If you’re interested in a visualization of the different factors scientists considered to explain rising temperatures before they landed on carbon dioxide, check out this video from CarbonBrief.

Photo credit: 350.org