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

Fact 2: Carbon dioxide is a greenhouse gas.

Given the two facts above, answer the question "Concentrations of what have increased over the last decade dramatically?" with the following options: 
- oxygen
 - harmful substances
 - light
 - greenhouse gases in the air
 - genetic diversity
 - Greenhouse gasses
 - basic building blocks of life
 - ozone


 

    greenhouse gases in the air     