Green solution in the ocean
Carbon dioxide, or Co2, is a naturally occurring gas compound, and the key element of the carbon cycle and a major component in photosynthesis. The core ingredient in CO2 is Carbon, which is the most common element (C) on the Periodic Table. There would be no life on Earth without carbon and its related compounds. However, over the last many years, drastic build-up of CO2 in the atmosphere has, ironically, begun to threaten the very life that the gas has helped create and sustain on the planet.
For the past 150 years, atmospheric CO2 has increased from 250 ppm to 418 ppm, being emitted through the extreme utilisation of fossil fuels. While the last 100 years of the Industrial Revolution have seen a significant rise in people’s living standards, amidst a sustained spell of industrial and inventive growth, the creature comforts have come at a costly environmental price. Consumerism, along with the dominance of gas-powered vehicles and pollution-inducing industrial processes across the world, have accelerated the release of CO2 into the atmosphere, resulting in climate change due to the greenhouse gas effect, further leading to global warming.
Besides the combustion/burning of fossil fuels, construction, manufacturing, and other industrial activities, alongside unbridled urbanisation, deforestation and stubble-burning have threatened whole ecosystems, taking the natural cycle in certain zones to almost irreversible levels. This has only amplified the ill-effects of CO2 emissions, causing the melting of the Polar ice caps, alteration in biogeochemical cycles, altered rainfall, ocean acidification, eutrophication (the gradual increase in the concentration of phosphorus, nitrogen, and other plant nutrients in an aging aquatic ecosystem) of lakes, imbalance in ecological communities, mass extinctions, soil infertility, changes in the metabolism and at the molecular level, and impact on people’s health.
According to Statista: “Global carbon dioxide emissions from fossil fuels and industry totalled 37.15 billion metric tons (GtCO2) in 2022. Emissions are projected to have risen 1.1% in 2023, to reach a record high of 37.55 GtCO2. Since 1990, global CO2 emissions have increased by more than 60%.” Emissions were found to have risen from 5 GtC/year to 9.9 GtC/year in the last 40 years.
World wakes up
The sporadic changes in weather patterns over the years, coupled with the unexpected seasonal cycles of heat waves, cold waves and rainfall across the globe, have exposed the urgent need to find ways to arrest the emission of CO2, and resuscitate an Earth built on sustainability and green practices.
“Immediate steps are required to confine the global temperature increase within 2°C and global carbon dioxide emissions to ∼1,100 GtCO2 between 2011 and 2050. However, with the current and predicted use of fossil fuels and various industrial activities, it is a challenging task, but there is also an opportunity to address it,” says a note from Indian Institute of Technology Madras.
Researchers across the globe have been racing to find solutions to contain emissions and fight climate change. A promising technique lies in the oceans.
Solution in the deep
Carbon sequestration, or CO2 sequestration, which is the process of capturing and storing atmospheric carbon dioxide, is a method of reducing the amount of CO2 in the atmosphere with the goal of reducing global climate change. The UN Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report defines CO2 sequestration as, “The process of storing carbon in a carbon pool.” A carbon pool refers to all the places where carbon on Earth can be, i.e. the atmosphere, oceans, soil, plants, and so forth. A carbon sink is a type of carbon pool capable of containing more carbon from the atmosphere than it releases.
On these lines, researchers at IIT Madras have identified that the Indian Ocean and Bay of Bengal can be potential storage sinks for storing large amounts of CO2. The CO2 sequestration process that they are working on envisages the ocean acting like a storage reservoir for greenhouse gas, which will help decarbonise industrial clusters.
The researchers found that carbon dioxide can be stored permanently in the ocean in the form of solid hydrate beyond 500 metres of sea depth through liquid CO2, thereby resulting in the country’s industrial clusters becoming carbon neutral.
Led by Prof Jitendra Sangwai from the Department of Chemical Engineering, and Yogendra Kumar Mishra, Research Scholar (Prime Ministers Research Fellow), at IIT Madras, the research has found that the novel process can help devise large-scale CO2 storage and utilise the fullest potential of oceans to decarbonise the world without harming marine ecology. This research can also help India achieve its national decarbonisation and climate change goals.
“The stored carbon dioxide can create an eco-friendly ice-like substance called ‘gas hydrates’. One cubic meter of gas hydrate can sequester approximately 150-170 cubic meters of CO2 under oceanic conditions beyond 500 meters,” the note reads, reiterating that gas hydrate-based storage holds massive potential to decarbonise India’s industrial clusters, and this research will pave pathways to develop large-scale sequestration in subsea sediments that help the scientific community fulfil India’s net-zero targets.
Highlighting the importance of this research to India, Prof Sangwai says, “Methane hydrates have been in the ocean for millions of years without affecting the environment. Methane is a more potent greenhouse gas than CO2. This attracts researchers to explore the ocean to store CO2 permanently. Our analysis shows that at above 2,800 m depth, CO2 is denser than seawater, which offers an additional gravitation barrier for CO2 to escape.”
Expressing the importance of CO2 sequestration in the oceans, he further explains: “Our dependence on fossil fuels will continue for the foreseeable future, till we find a reliable source of energy to completely replace them. Thus, CO2 capture and sequestration is a very important precursor to achieve net-zero goals. Once CO2 is captured from source, it needs to be sequestered safely. CO2 sequestration in oceans will be beneficial to India as, according to a conservative estimate, the Bay of Bengal alone can sequestrate several hundred giga tonnes of anthropogenic CO2 in oceans and marine sediments, which is equivalent to several years of total GHG (greenhouse gas) emission released by India. Some European countries (eg. Norway and Denmark) are working on CO2 storage in the North Sea.”
Once the CO2 is permanently stored as a gas hydrate, it does not allow for any reemission into the atmosphere, owing to gravitational and hydrate permeability barrier in the subsea sediments.
Elaborating, Mishra says, “There are different ways to sequester CO2 to reduce its impact on the environment. Using the ocean as a CO2 storage sink is an attractive proposition, but storing CO2 directly into the ocean at shallow depth can harm marine life. Hence, CO2 needs to be stored permanently in the ocean in the form of liquid pools or solid hydrates beyond a certain depth.”
“Another attractive option is to store CO2 in subsea sediments as this will have less impact on marine ecology. The subsea sediments have tiny spaces that can hold CO2, and over the period of time, stored gas forms ice-like gas hydrate crystals in the pores, which will further reduce the permeability of hydrate-bearing sediments and create a permeability barrier,” suggests Mishra.
Going net-zero
The IIT Madras team has observed that hydrate formation is more efficient and stable at higher clay concentrations. The clay inclusion in seawater improves the kinetics of hydrate formation as compared to seawater alone.
Certain promoters such as tetrahydrofuran (THF) further enhance hydrate kinetics synergistically with clay that will help in large-scale CO2 storage in subsea sediments. Studying the concentration of clay, properties of additives, and local bathymetry information of the ocean can help figure out the best way to store CO2 in the subsea sediments.
At the 26th session of the United Nations Framework Convention on Climate Change (COP 26) in November 2021, India announced its effort to achieve net-zero targets by 2070. With the vision to lead the fight against global climate change, the country has announced a range of policies including, committing to secure 500 GW of renewable energy installed capacity by 2030.
Additionally, it looks to produce 5 MT of green hydrogen by the same year, supported by 125 GW of RE capacity. Separately, 50 solar parks with an aggregate 37.49-GW capacity are on the anvil. These missions, complemented by cutting-edge research in areas such as CO2 sequestration, will benefit the country and the world at present and in the future.
Why CO2 matters
Carbon dioxide is essential for photosynthesis - the process by which plants produce their own food; in turn the vegetation releases oxygen into the atmosphere for us to breathe. CO2 is the Earth’s most important greenhouse gas, which absorbs and radiates heat. According to the US’ National Oceanic and Atmospheric Administration: “Unlike oxygen or nitrogen (which make up most of our atmosphere), greenhouse gases absorb heat radiating from the Earth’s surface and re-release it in all directions — including back towards the planet’s surface.”
Without Co2, Earth’s natural greenhouse effect would be too weak to keep the average global surface temperature above freezing. By adding more CO2 to the atmosphere, people are supercharging the natural greenhouse effect, causing global temperature to rise. According to observations by the NOAA Global Monitoring Lab, in 2021, CO2 alone was responsible for about two-thirds of the total heating influence of all human-produced greenhouse gases.
Carbon dioxide concentrations are rising mostly because of the fossil fuels that people are burning for energy. Fossil fuels like coal and oil contain carbon that plants pulled out of the atmosphere through photosynthesis over millions of years, which is being returned to the atmosphere in just a few hundred years, leading to a climate crisis.
Types of carbon sequestration
Geologic carbon sequestration is the process of storing carbon dioxide (CO2) in underground geologic formations. The CO2 is usually pressurized until it becomes a liquid, and then it is injected into porous rock formations in geologic basins
Biologic carbon sequestration refers to storage of atmospheric carbon in vegetation, soils, woody products, and aquatic environments. Oceanic sequestration falls under this process category
Key findings of the research
Beyond 2,800 metres of sea depth, CO2 liquid is denser than seawater
Thus, beyond 2800 metres sea depth, CO2 can be stored permanently in the form of liquid pool and solid hydrate
It will not permit any reemission into the atmosphere owing to the gravitational and permeability barrier offered by subsea sediments
The subsea clay sediments improve the mechanical and thermal stability of gas hydrates which help for long-term CO2 storage potential
Source: IIT Madras