Which piece of evidence is not supported by a source?

The question asks to identify which piece of evidence is not supported by the provided text. Let's analyze each option against the text.

The text states: "The troposphere's average temperature has not changed in 23 years. If there were global warming occurring, contends the API, temperatures should be rising in the troposphere. Because they are not rising, some scientists argue that climate change does not exist on an atmospheric scale and will not lead to disastrous results."

• Option 1: "... the troposphere's average temperature has not changed in 23 years." This statement is directly supported by the first sentence of the text.

• Option 2: "These rising levels... could lead to a greenhouse effect, causing increased surface temperatures on the earth." The text discusses "global warming" and "climate change" and "disastrous results," which are related to the greenhouse effect and increased temperatures. However, the text does not explain the mechanism of the greenhouse effect, mention "rising levels" of specific gases, or explicitly state that these lead to increased surface temperatures. While related to the topic, this specific explanation is not provided in the text.

• Option 3: "Carbon dioxide is released into the atmosphere when organic material decays, volcanoes erupt, and when fossil fuels are burned." The text does not mention carbon dioxide, organic material decay, volcanoes, or fossil fuels at all. This information is entirely absent from the provided passage.

• Option 4: "If there were global warming occurring, temperatures should be rising in the troposphere." This statement is directly supported by the second sentence of the text, which states, "If there were global warming occurring, contends the API, temperatures should be rising in the troposphere."

Comparing options 2 and 3, option 3 introduces specific scientific terms and concepts (carbon dioxide, its sources) that are completely unmentioned in the passage. Option 2, while not explicitly detailed, discusses the effects of global warming, which is the central topic of the passage. Therefore, option 3 is the most definitively unsupported by the provided source.

The final answer is $\boxed{\text{Carbon dioxide is released into the atmosphere when organic material decays, volcanoes erupt, and when fossil fuels are burned.}}$