Natural short-lived halogens exert an indirect cooling effect on climate
In addition to absorbing carbon dioxide and moderating the climate, the oceans keep Earth cool by releasing short-lived halogens (SLHs) such as chlorine, bromine and iodine, according to a study recently published in Nature.
- Currently, these halogens contribute 8-10% of cooling. It is estimated that this may increase to 18-31% by 2100. Short-lived halogens have a lifetime of less than six months in the atmosphere.
- They are produced naturally by the oceans, polar ice, and the biosphere. However, human activities have increased their release from the ocean into the atmosphere.
- Natural sources of short-lived halogens include both biogenic and abiotic sources. Biogenic sources include nine halocarbons that are the result of phytoplankton metabolism associated with micro- and macro-algae as well as photochemistry at the sea surface.
- Human activities cause pollutants such as ozone to accumulate in the ocean, which then convert soluble short-lived halogens into insoluble ones, allowing them to escape from ocean water into the atmosphere.
- Halogens cause ozone depletion in the troposphere. Ozone is a greenhouse gas that traps outgoing radiation, causing an increase in temperature. Short-lived halogens released from the oceans reduce warming by depleting ozone.
- The short-lived halogens extend methane lifetime in the atmosphere by scavenging hydroxyl radicals (OH). OH is a sink and it is known to break down the greenhouse gas methane.
- These halogens also increase the level of the greenhouse gas water vapors in the atmosphere.
- These short-lived halogens reduce the formation of cooling aerosols, which are suspended particles in the atmosphere that reflect sunlight.
Source – Down to Earth