Earth's atmosphere now has 404 parts of carbon dioxide for every million parts of air.
What does this number mean?
Earth's global average temperature is 1.7º hotter than it was in 1880.
Why is this small number a big deal?
The area of the Arctic Ocean covered by sea ice in 2015 was only 64% as large as it was in 1979.
What is happening to the ice?
The global average sea level has risen 3.4 inches in the past 23 years.
What if it keeps rising this fast?