Which one among the following is responsible for the expansion of water in the ocean ?

Carbon dioxide (CO2) is the primary greenhouse gas responsible for the expansion of water in the ocean. Human activities, particularly the burning of fossil fuels, have led to increased atmospheric concentrations of CO2, which trap heat through the enhanced greenhouse effect [5]. The ocean acts as a massive heat sink, absorbing more than 90% of this excess heat generated by greenhouse gas emissions [6]. As the ocean absorbs this heat, its temperature rises, leading to thermal expansion—a process where water molecules move further apart, increasing the overall volume of ocean water [2]. This thermal expansion is a major driver of global sea-level rise [3]. While other gases like nitrogen dioxide and sulphur dioxide are atmospheric pollutants, they do not play the same dominant role as CO2 in the sustained global warming and subsequent thermal expansion of the oceans.

Sources

1. [4] https://www.noaa.gov/basics-of-carbon-cycle-and-greenhouse-effect
2. [5] https://www.epa.gov/ghgemissions/overview-greenhouse-gases
3. [1] https://earth.gov/sealevel/faq/104/what-are-the-connections-between-emissions-temperature-change-and-sea-level-rise/
4. [6] https://www.un.org/en/climatechange/science/climate-issues/ocean
5. [2] https://sealevel.nasa.gov/understanding-sea-level/global-sea-level/thermal-expansion/
6. [3] https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content