Human actions are causing Earth to warm by increasing the amount of carbon dioxide in the atmosphere. Today, there's more carbon dioxide in the air than anytime in at least 800,000 years. That's 8,000 centuries!

When we burn fossil fuels, we are rapidly releasing carbon that had been locked within Earth into the atmosphere. This carbon combines with oxygen in the air to form carbon dioxide.

Another way humans are increasing carbon dioxide levels is by cutting down trees. Trees are like sponges that remove carbon dioxide from the air through photosynthesis. To make matters worse, we also burn trees. This quickly releases carbon dioxide into the atmosphere.