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

Fact 2: Increases in carbon dioxide make the greenhouse effect worse.

Given the two facts above, answer the question "How has the greenhouse effect changed in the last decade?" with the following options: 
- moved to South America
 - improved
 - Temperature
 - fossil fuels
 - has become cooler
 - worsened
 - climate
 - growth


 

      worsened   