Please choose the correct answer to the question: This in turn causes the average temperature on Earth to rise. Which of the following observations supports that theory?

Answer1: The summer of 1998 was one of the hottest summer seasons on record. Answer2: Carbon dioxide gas from cars and industry is a product of burning that produces heat. Answer3: Carbon dioxide in the upper atmosphere absorbs and re-emits heat radiated from Earth's surface. Answer4: Radiation on Earth's surface is increasing because of a hole in the ozone layers.

Answer format: answer1/answer2/answer3/answer4