Oceans' Short-Lived Halogens

• 30 Jun 2023

Recently, a study revealed that oceans play a crucial role in cooling the planet by releasing short-lived halogens such as chlorine, bromine, and iodine.

• Significant Contribution to Cooling: Short-lived halogens, including chlorine, bromine, and iodine, released by the oceans contribute to cooling the planet. Currently, they contribute 8-10% of cooling, which could increase to 18-31% by 2100.
• Amplification of Halogen Release: Human activities have amplified the release of short-lived halogens into the atmosphere. Pollutants, such as ozone, deposited on the ocean surface convert soluble halogens into insoluble ones, causing their release into the atmosphere.
• Depletion of Ozone: Short-lived halogens lead to the depletion of ozone in the troposphere. This depletion reduces warming as ozone is a greenhouse gas that traps outgoing radiation.
• Impact on Methane: Short-lived halogens have an opposite effect on methane. They increase methane's lifetime in the atmosphere by destroying hydroxyl radicals (OH), which break down methane. This leads to a warming effect due to increased methane levels.
• Influence on Water Vapour and Aerosols: Short-lived halogens increase the levels of water vapour, a greenhouse gas, in the atmosphere, causing a warming effect. They also reduce the formation of cooling aerosols, resulting in a small warming effect.
• Net Cooling Effect: Despite their influence on methane, water vapour, and aerosols, short-lived halogens compensate for warming by destroying ozone, resulting in a net cooling effect.
• Regional Variations: Halogen emissions from the oceans vary across regions. Emissions are small over continents, larger in polar regions and in areas with higher ozone levels.
• Anthropogenic Amplification: The cooling effect of chlorine, bromine, and iodine since the preindustrial era has increased by 61% due to the amplification of natural halogen emissions by human activities.