Option 1: Automobile exhaust fumes are not a direct source of methane emissions. Methane is primarily produced from the decomposition of organic matter in anaerobic conditions.

Option 2: Industrial chimneys are not a direct source of methane emissions. Methane is mainly released during the extraction and distribution of coal, oil, and natural gas.

Option 3: Mining activities are not a direct source of methane emissions. Methane is released from coal mines during the mining process, but this does not occur in all types of mining.

Option 4: Wetlands are a significant natural source of methane emissions. Wetlands, such as marshes and swamps, contain decomposing organic matter that produces methane through anaerobic processes.

The correct answer is option 4 because wetlands are a natural source of methane emissions. Methane is produced by microbes in wetland environments as they decompose organic matter. This methane is then released into the atmosphere. It is important to note that while wetlands are a significant source of methane, human activities such as rice cultivation can also contribute to methane emissions from wetlands.