According to a recent study published in Nature, apart from absorbing carbon dioxide and moderating the climate, oceans cool the planet by releasing short-lived halogens (SLH) such as chlorine, bromine and iodine.
Key points
- Currently, these halogens contribute 8-10 per cent of cooling. This could increase to 18-31 per cent by 2100, the projected.
- Short-lived halogens have a lifetime of less than six months in the atmosphere.
- They are naturally produced by the oceans. However, human activities have amplified their release into the atmosphere.
- Natural SLH sources include both biogenic and abiotic pathways. Biogenic sources comprise nine halocarbons which are the result of micro- and macro-algae as well as phytoplankton metabolism coupled to photochemistry at the ocean’s surface.
- Human activities cause pollutants such as ozone to deposit on the ocean, which then convert the soluble short-lived halogens into insoluble ones, forcing them out of the sea water and into the atmosphere.
- Halogens cause a depletion of ozone in the troposphere. Ozone is a greenhouse gas that traps outgoing radiation, leading to warming.
- Short-lived halogens from oceans reduces warming by depleting ozone.
- Short-lived halogens increase methane’s lifetime in the atmosphere by destroying hydroxyl radicals (OH). OH is a sink as it is known to break down this greenhouse gas. These short-lived halogens increased global methane burden by 14 per cent and 9 per cent for pre-industrial and present-day conditions, respectively.
- These halogens increase the levels of water vapour, a greenhouse gas, in the atmosphere.
- These short-lived halogens reduce the formation of cooling aerosols, which are minute particles suspended in the atmosphere that reflect sunlight.
