As concentrations of CFC-11 in the atmosphere decline, the global oceans will become one of the sources of the chemical by the middle of the next century. The world’s oceans are a vast reservoir of gases, including ozone-depleting HCFCs (CFCs). They absorb these gases from the atmosphere and then take them to the depths of the ocean floor, where they are isolated for centuries or more.
Marine CFCs have long been used as tracers for ocean current research, but their effects on atmospheric concentrations are considered negligible. Now, researchers at the Massachusetts Institute of Technology (MIT) have found that at least one type of CFC called CFC-11 does affect atmospheric concentrations. A study published today in Proceedings of the National Academy of Sciences says the global oceans will change their role as containers of powerful ozone-depleting chemicals for a long time.
The researchers predict that by 2075, the oceans will emit more greens into the atmosphere than they absorb, and 2130, their emissions will reach detectable levels. Moreover, as climate change intensifies, this shift will occur 10 years ahead of schedule. CFC-11 emissions from the ocean will effectively extend the average stay of the chemical, allowing it to stay in the atmosphere for five years longer than other methods. This may affect future estimates of foreign emissions.
The new findings could help scientists and policymakers better identify future sources of the chemical. Currently, the chemical is banned worldwide under the Montreal Protocol.
CFC-11 is a chlorofluorocarbon commonly used to make refrigerants and insulation foams. When released into the atmosphere, the chemical triggers a chain reaction and eventually destroys the ozone layer, which protects the planet from harmful ultraviolet radiation. Since 2010, the production and use of the chemical have been phased out worldwide under the Montreal Protocol, a global treaty aimed at restoring and protecting the ozone layer.
Since its phase-out, atmospheric fluorine levels have been steadily declining, with scientists estimating that the ocean absorbs 5 to 10 percent of all man-made emissions. However, as concentrations of HCFCs in the atmosphere continue to decline, HCFCs in the oceans are expected to become oversaturated, making them a source of pollution.
In their study, the MIT team tried to determine when the ocean becoming a source of the chemical and how much the ocean affected the concentration of free in the atmosphere. They are also trying to understand how future climate change will affect the ocean’s ability to absorb chemicals.
The researchers used layered models to simulate the mixing of oceans and atmospheres. They first built a simple atmospheric model and the upper and lower layers of the oceans of the northern and southern hemispheres. They added previously reported man-made emissions of Freon to the model and then ran the model in chronological order — from 1930 to 2300 — to observe changes in the flow of chemicals between the ocean and the atmosphere.
They then replaced the ocean layer of the simple model with a more complex model of ocean dynamics, the MIT Global Climate Model (MITgcm), and performed a similar simulation of Freon over the same period.
The levels thrown in the atmosphere from both models matched the recorded measurements to this day, giving the team confidence in their approach. When they studied the model’s predictions for the future, they observed that starting around 2075, the oceans began to emit more chemicals than they absorbed. By 2145, the number of CFCs-11 emitted from the ocean will be detected by current monitoring standards.
Ocean absorption and future emissions in the 20th century will also affect the effective stay of chemicals in the atmosphere, with a reduction of several years during absorption and an increase of five years by the end of 2200.
Also, climate change will accelerate this process. The team used these models to simulate the future of global warming of about 5 degrees Celsius by 2100 and found that climate change would shift the oceans to a source for 10 years and produce detectable France by 2140.
“Generally, cold oceans absorb more HCFCs,” says researcher Peidong Wang. ”
“Even without climate change, because CFCs decay in the atmosphere, the ocean will eventually come back with too much content relative to the atmosphere. (So) we think climate change will make this happen earlier. But this shift does not depend on climate change,” Solomon added.
Study simulations show that oceans shift slightly faster in the northern hemisphere, where large-scale ocean current patterns are expected to slow down, allowing more gas to escape back into the atmosphere in shallow seas. However, more detailed models are needed to understand the exact cause of ocean reversals, and the researchers plan to explore this.
“The next thing to do is to do this with a higher resolution model and focus on changing patterns. So far, we’ve raised some big new questions and given an idea that people might see,” said researcher Jeffrey R. Scott. Paleontologists have discovered hatching fossils of egg-stealing dragons.