The Southern Ocean may be causing a massive burp

The ocean has helped mitigate global warming by absorbing about a quarter of anthropogenic carbon dioxide (CO₂), as well as more than 90% of the excess heat generated by these emissions.

Many efforts, including assessments from the Intergovernmental Panel on Climate Change, have examined how oceans could continue to mitigate increasing emissions and global warming. However, few have considered the opposite: how will the oceans respond if emissions and associated atmospheric heat levels begin to decline in response to net negative emissions?

Ivy Frenger and her colleagues examined what could happen in the Southern Ocean if, after more than a century of human-induced warming, global average temperatures were to be reduced via CO.₂ withdrawal from the atmosphere. Their results are published in the journal AGU progress.

The Southern Ocean is a dynamic system, with large-scale upwellings and a strong capacity to absorb excess carbon and heat. To better understand how the Southern Ocean would behave under net-negative carbon conditions, researchers modeled how the ocean and atmosphere would interact.

They used the University of Victoria climate model, UVic v. 2.9, to simulate multi-century time scales and carbon cycle feedbacks. UVic uses a combination of an atmospheric energy-moisture balance model, an ocean circulation and sea ice model, a terrestrial biosphere model, and an ocean biochemistry model.

The researchers used UVic to model an idealized climate change scenario commonly used in climate modeling: emissions increase until atmospheric CO₂ levels double after age 70, followed by a sharp reduction in emissions and sustained net negative emissions.

The results showed that after several centuries of negative net emissions levels and gradual global cooling, the Southern Ocean abruptly released an explosion of pent-up heat – an ocean “burp” – that led to a period of warming on the decadal or centennial scale. This warming was comparable to average historical anthropogenic warming rates. The team said that due to the unique chemistry of seawater, this burp released relatively little CO₂ with the heat.

Frenger and colleagues note that their work uses an intermediate complexity model and an idealized climate change scenario, but that their results were consistent when tested with other modeling setups. They say the importance of the Southern Ocean to the global climate system, including its role in releasing heat into the atmosphere in a cooling climate, should be studied further and contemporary changes closely monitored.

This story is republished courtesy of Eos, hosted by the American Geophysical Union. Read the original story here.