Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: The atmosphere contains small amounts of carbon dioxide. Climatologists have found that humans are putting a lot of extra carbon dioxide into the atmosphere. This is mostly from burning fossil fuels. The extra carbon dioxide traps heat from the Sun. Trapped heat causes the atmosphere to heat up. We call this global warming ( Figure below ). Answer: carbon dioxide
Which gas is responsible for global warming?