Climate Change and the role played by Oceans

Subject :Environment

Section: Climate change

Context:

Oceans cool the planet by releasing short-lived halogens that contribute 8-10 per cent of cooling: Stud

Study findings:

Ocean absorbs the carbon and moderates the climate.
They also cool the planet by releasing short-lived halogens such as chlorine, bromine and iodine.
Currently, these halogens contribute 8-10 per cent of cooling. This could increase to 18-31 per cent by 2100.
Climate models that make future projections do not account for this.
The cooling by chlorine, bromine and iodine since the preindustrial era has risen by −0.05 ± 0.03 watts per square metre, which represents a 61 per cent spike. This is driven by the anthropogenic amplification of natural halogen emissions.

Short-lived halogens:

Naturally produced by the oceans.
They have a lifespan of six months.
Human activities have amplified their release into the atmosphere.
Halogen emissions from the ocean are not the same across the world.
Over continents, the emissions are small while it is bigger in polar regions and some places with higher ozone levels.
How do they moderate the effects of global warming?
Human activities cause pollutants such as ozone to deposit in the ocean, which then convert the soluble short-lived halogens into insoluble ones, forcing them out of the seawater and into the atmosphere.

Impact of short-lived halogens on the substances that causes global warming:

Ozone:
- Halogens cause a depletion of ozone in the Ozone is a greenhouse gas that traps outgoing radiation, leading to warming.
- The short-lived halogens from oceans reduce warming by depleting ozone. Its cooling effect was -0.24 ± 0.02 Watts per square metre (W m−2).
Methane:

However, their effect on methane is the opposite. 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 the global methane burden by 14 per cent and 9 per cent for pre-industrial and present-day conditions, This leads to a warming effect of 0.09 ± 0.01 W m−2 of warming.

Similarly, these halogens increase the levels of water vapour, a greenhouse gas, in the atmosphere, causing a warming effect of 011 ± 0.001 W m−2.

These short-lived halogens reduce the formation of cooling aerosols, which are minute particles suspended in the atmosphere that reflect sunlight. It causes a small warming of 03 ± 0.01 W m−2.

The overall impact of these short-lived halogens:

Though these halogens drive an increase in warming by influencing methane, water vapour and aerosols, they compensate this by destroying ozone, which exerts a cooling effect.

Overall, the net cooling effect was found to be −0.13 ± 0.03 W m−2.