Final answer:
Oxygen (O3) is the gas from the provided options that is not considered a significant contributor to global warming. The major contributors are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which trap heat in the atmosphere.
Step-by-step explanation:
The gas that is not considered a significant contributor to global warming from the options provided is d) oxygen (O3). The major gases contributing to the greenhouse effect and, consequently, global warming, are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). These gases are able to trap heat in the Earth's atmosphere due to their molecular structure, which allows them to absorb and emit infrared radiation.
Carbon dioxide, the primary greenhouse gas affecting climate change, is released through activities such as the burning of fossil fuels and deforestation. Methane is a potent greenhouse gas with a global warming potential significantly higher than CO2. It is emitted during agricultural production and by the decomposition of organic waste in landfills. Likewise, nitrous oxide, another powerful greenhouse gas, is primarily released from agricultural practices, such as the use of pesticides and soil cultivation processes. Oxygen, on the other hand, does not absorb thermal infrared radiation as the other three do and therefore, is not considered an important greenhouse gas.