Fact 1: Carbon dioxide concentrations in the air have increased over the last decade dramatically.

Fact 2: Carbon dioxide is the primary greenhouse gas.

Given the two facts above, answer the question "What have increased over the last decade dramatically" with the following options: 
- gasoline concentrations
 - Warm air moving into cold air
 - Greenhouse gases
 - treehouse gas concentrations
 - movements in the earth's crust
 - concentrated orange juices
 - genetic diversity
 - greenhouse gas concentrations


 

        greenhouse gas concentrations 