Option 1: Solid waste treatment can cause methane emissions and contribute to global warming. Methane is produced during the decomposition of organic matter in landfills. When solid waste is not properly managed and disposed of, methane is released into the atmosphere, where it is a potent greenhouse gas.

Option 2: Natural wetlands can also cause methane emissions and contribute to global warming. Wetlands, such as swamps and marshes, have anaerobic conditions that promote the production of methane. Methane is generated by the breakdown of organic matter in these environments.

Option 3: Ruminant animals, such as cows, sheep, and goats, can produce methane as a byproduct of their digestion process. Certain microorganisms in their digestive system break down the food they eat and produce methane as a result. This methane is then released through belching and flatulence.

The correct answer is option 4, which includes all of the above options. Solid waste treatment, natural wetlands, and ruminant animals are all sources of methane emissions and therefore contribute to global warming. They release methane, a potent greenhouse gas, into the atmosphere, trapping heat and contributing to climate change.