In simplified terms, climate change boils down to having carbon in the wrong place.
“Carbon is stored in the Earth’s crust, plants, oceans and the atmosphere. The climate’s behaviour is largely determined by the circulation of carbon between these reservoirs,” explains Tuomo Kalliokoski, university researcher in forest ecology at the Institute for Atmospheric and Earth System Research, University of Helsinki.
Carbon has always circulated from one reservoir to another, but according to Kalliokoski’s estimate, humans have accelerated the carbon cycle from crust to atmosphere at least ten-fold.
Now that the Intergovernmental Panel on Climate Change (IPCC) is sounding the clarion call, new means are needed to capture carbon dioxide from the atmosphere.
According to a study published in the Science journal in July, the planet has room for a trillion more trees to be planted. The area required is the equivalent of the combined area of the United States and China. This would result in the removal of as much as two-thirds of human-induced emissions from the atmosphere. Some researchers have doubted such findings, while IPCC calculations show that new forests would be able to bind roughly 25% of the amount projected in the article by the end of this century.
Forests have a significant role in the sequestration of carbon dioxide, but researchers are putting an emphasis on the big picture. Where else can carbon be captured?
Manure on the field
Growing carbon reservoirs become carbon sinks, while diminishing ones turn into carbon sources.
“I wish the conversation would revolve around carbon reservoirs instead of carbon sinks,” Kalliokoski notes.
When focusing on carbon sinks, one may start to think that Finland’s forests should be kept young and healthily growing. Were Finnish forests to be cut down at 30–40-year intervals, carbon sinks would be large, as young trees grow faster than old ones. However, carbon reservoirs would not be preserved, as the carbon captured by the felled forests quickly returns to the atmosphere.
What enriches carbon reservoirs is processing timber into durable products, such as buildings. This, however, would require a significant change in the use of timber, as currently only a fraction ends up in durable products. Paper and bio-energy are rapid-cycle products, and the carbon fixed by them is quickly returned to the atmosphere.
Finland’s forest area is decreasing due to the continued clearing of forests to make room for fields, in part a result of the centralisation of EU-supported agriculture. When cattle farms grow in size, they need more space for manure spreading, that is, fields.
“When forests are cleared off, carbon reservoirs are lost. At the worst, manure is spread in the cleared area, resulting in emissions from decomposition,” Kalliokoski points out.
What about peatlands? Could they capture more carbon? At least they serve as sizeable carbon reservoirs, containing one-third of all carbon stored in the soil, even though they only cover three per cent of Earth’s land surface.
“Peatlands are an enormous carbon sink and reservoir, but long-term and slow in the nature of their cycle,” says Mari Pihlatie, an associate professor specialised in ecosystem processes at the Faculty of Agriculture and Forestry, University of Helsinki.
Over millennia, dead plants accumulate in peatlands. Gradually, this organic matter turns into peat, which decomposes in oxygen-low or oxygen-free conditions so slowly that, over time, peat has time to absorb great deals of carbon.
Still, most of the carbon stored in peatlands circulates back to the atmosphere in the form of carbon dioxide and methane, a product of oxygen-free decomposition. Even at its best, only approximately 15% of the carbon ends up as reservoirs in peat. In the long term, however, more carbon is captured than released by peatlands.
Two distinct types
One way to sequester carbon is to restore peatlands that have previously been drained for the purposes of commercial forestry and land cultivation.
When peat interacts with the oxygen found in the air, it decomposes rapidly. Raising water levels in peatlands would slow down this process. However, trees growing on drained peatlands currently store more carbon compared to the emissions caused by peat decomposition.
Furthermore, peatlands come in different types. In nutrient-rich peatlands decomposition is rapid and emissions greater, whereas barren peatlands are more effective as carbon sinks.
“Letting trees grow and ditches close in nutrient-rich peatlands could be an efficient method,” Kalliokoski speculates.
This would raise the water level and slow down the decomposition of peat. Restoration by blocking ditches is another efficient way to reduce peat decomposition in nutrient-rich peatlands.
“The carbon sink activity of trees will be reduced, but the carbon reservoir remains undisturbed if trees are not cut,” Kalliokoski says.
Consigning clear-cutting to history
The largest carbon reservoirs on Earth are found in forests. Rough forestry practices, entailing the cutting down and ploughing of entire forests, releases carbon into the atmosphere.
Soil cultivation leads to the break-up of organic matter and the release of nutrients, causing many organisms partial to such change to start breaking down carbon compounds found in the soil at an accelerating pace. Rain also washes carbon and nutrients away from terrain that has become treeless after clear-cutting.
Mari Pihlatie is in favour of continuous cover forestry, which produces forests with trees of different ages, felled only a part at a time. The soil remains covered by vegetation, keeping the carbon fixed.
“If clear-cutting was discontinued and forestry was based on the continuous cover method, forests would capture carbon and remain carbon sinks.”
Two-class field system
Carbon is also released by fields. Over the centuries, soil becomes less fertile. Fields too should be continuously covered by vegetation in order for them to keep storing carbon in the soil and fostering diversity.
Mineral-rich fields that have been cultivated for a long time and that have released their carbon could be used to capture more carbon. Adopting new farming techniques all over the world would have significant consequences. Pihlatie believes that farmers need more information on carbon sinks and new practices in order to understand their benefits.
In many corners of the world, peatlands have been drained for the purposes of agriculture and forestry. Large quantities of carbon are stored in such peatlands. As the peat found in drained peatlands interacts with oxygen, the stored carbon degrades, resulting in considerable emissions. The greenhouse gas emissions of dry peatlands constitute as much as 1 gigaton every year globally.
“Even a reforested peat field emits greenhouse gases for decades to come, making the continued cultivation of productive fields potentially the best option,” Pihlatie says.
In peat fields phased out of use, water levels could be raised to restore them to peatlands and slow down the decomposition of peat.
Is nature strong enough?
Current climate goals require that the land-use sector – forests, wetlands, arable land and fields – should be turned into carbon sinks by 2030. In the subsequent decades, these sinks should be quickly strengthened.
In late 2018, the IPCC published a number of scenarios on how the warming of the climate could be stopped at 1.5 degrees Celsius. The reliance on carbon sinks varied by scenario, but all of them depended on technology alongside the environment. The most prominent measure in the plans is BECCS, or producing bio-energy with carbon capture and storage.
In its estimates, the panel proposes intensifying bio-energy production to eight times the current level and capturing the resultant carbon dioxide. This would entail 500 million additional hectares for the plants used to produce bio-energy.
Putting a cap on emissions
The majority of the Earth’s surface is already in use. To provide enough food for everyone and to maintain natural carbon sinks at the current level, existing fields and forests cannot be taken into account when calculating the required additional land area. Bio-energy production should not endanger food production.
“If bio-energy production is increased poorly, it may clash with boosting carbon sinks,” Kalliokoski says.
As well as carbon sinks, rapid emission reductions are needed. In the spring scientists stressed in the Science journal that a decade’s delay in reducing emissions may lead to emission levels of such magnitude that they would reverse the effect of natural carbon sinks.
Capturing carbon from the smokestack
Carbon reclamation techniques are already being employed in, among others, China, the United States, Norway and the United Kingdom. Some facilities are only functioning at an experimental stage; others already capture carbon at an annual rate close to a million tons. Fortum, a Finnish energy company, is taking part in a CCS project in Oslo.
CCS denotes carbon capture and storage technology. Carbon dioxide is captured either before or after combustion and subsequently transported via a pipeline or with trucks for storage in disused oil fields or elsewhere in the Earth’s crust.
In Finland and Norway, attitudes towards experiments are more positive than, for example, in Germany where CCS projects have been cancelled due to civic opposition,” says University Researcher Farid Karimi from the University of Helsinki.
“Attitudes are affected by cultural factors that influence opinions,” adds Karimi, who specialises in the social acceptance of carbon capture techniques.
China, India, Canada, Australia and the United States continue to rely on fossil fuels, with their vast stores of coal keeping the costs low. It is difficult to convince these countries to completely switch over to using renewable energy.
“With the help of technology, we can demonstrate to the countries burning up fossil fuels that if you choose to pollute, then the least you can do is clean up after yourselves.”
Carbon capture is needed, at least in fields where reducing emissions is difficult, such as the steel and cement industries.
What represents the biggest obstacle for adopting CCS is the cost. In the absence of quick results and popularity, decision-makers avoid making investments. Furthermore, concerns are raised by questions of responsibility. Who is responsible for carbon dioxide leaks from capture sites? How long should the party carrying out the capture remain responsible for any potential leaks?
In the European Union, the period of liability for carbon dioxide capture businesses is 20 years. The rules are yet to be tested, as no carbon dioxide storage sites under European projects have yet been closed.
What does the model reveal?
The development of carbon sinks is assessed by employing a range of models. When comparing models for the development of Finland’s carbon balance, the Finnish Climate Change Panel found that their predictions varied greatly. At the extremes, the effect of logging on carbon sink development varied to the entire extent of Finland’s current emissions.
The models were unable to accurately forecast the carbon balance of the soil, or how much the soil will fix or release carbon in the future. To develop increasingly accurate models, more information is needed on how large a share of the carbon fed by plants into the soil remains there and how much is returned to the atmosphere in conjunction with microbial decomposition activity, also known as soil respiration.
One result remained unchanged in all models: the fewer trees are cut, the larger the carbon reservoir of the forest is.
Do researchers disagree on the size and importance of carbon sinks?
“Often it’s about the perspective. One researcher may make assumptions about the financial benefits of forestry, while another approaches the issue from the point of view of natural sciences,” forest ecologist Tuomo Kalliokoski says.
In the report by the Finnish Climate Change Panel, all of the researchers were in agreement regarding the fact that increased logging decreases the carbon sink and carbon reservoir capabilities of Finnish forests for several decades at least.
Researchers are often asked to what extent trees can be cut down within the limits of the climate goals. That number is impossible to determine. According to Kalliokoski, a level of cutting sustainable in terms of the climate depends on what is done elsewhere in society.
Will logging intensify? Will timber be processed into chemical pulp and short-lived products? How will traffic evolve? Questions associated with cost-efficiency calculations and their mutual comparisons are mudding the waters of public discourse.
The article was previously published in Finnish in the Y/05/19 issue of Yliopisto-lehti.