Greenhouse Effect and Human Activity 1. What would happen if there was no greenhouse effect on earth? 2. What are the four main greenhouse gases in the atmosphere? 3. What do you predict would happen if more greenhouse gases are added to the atmosphere? 4. What human activities add greenhouse gases to the atmosphere? 5. How will the increasing temperature impact other things on earth? 6. What can you do to help reduce greenhouse gas emissions? See graphs below to help with your answer.