Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: This in turn causes the average temperature on Earth to rise. Which of the following observations supports that theory?
Carbon dioxide in the upper atmosphere absorbs and re-emits heat radiated from Earth's surface.
The global temperature is increasing.