You are presented with the question "What has led to the increase in global warming?" and the following answer choices: 
- Greenhouse gases
 - movements in the earth's crust
 - Increase in carbon dioxide
 - Greenhouse gasses
 - forest is destroyed
 - Burning fuel and air
 - movement of tectonic plates
 - tectonic plates being pushed together

Now knowing that carbon dioxide concentrations in the air have increased over the last decade dramatically and carbon dioxide is the chief culprit in the increased threat of global warming in recent decades, choose the best answer.


 

   Increase in carbon dioxide      