Ocean water contains large quantities of dissolved gases, including oxygen, carbon dioxide and nitrogen. This gas exchange takes place at the ocean surface and solubility depends on the temperature and salinity of the water. The increasing concentration of carbon dioxide in the atmosphere due to fossil fuel combustion leads to higher concentrations in ocean water, resulting in ocean acidification. The ocean provides society with important environmental services, including climate regulation. It also offers a means of trade and transport and access to food and other resources. Known to be the habitat of over 230,000 species, it may contain far more – perhaps over two million species. However, the ocean is subject to numerous environmental threats, including marine pollution, overfishing, ocean acidification and other effects of climate change. The continental shelf and coastal waters that are most influenced by human activity are especially vulnerable.