Everyone blames greenhouse gases such as CO2. However, CO2 is not the devil. If there were no greenhouse gases, what would happen? The average temperature of the Earth is about +14 °C in the 20th century. However, in the absence of greenhouse gases, the temperature would dr0p to -15°C. In this way, greenhouse gases such as CO2 make the earth's temperature suitable for life. Well, you might think that the temperature can drop that much in a cold winter. However, the average temperature of the Earth about 20,000 years ago, during the last glacial period of the Earth, was about +7 or +8 °C. The average temperature differs quite a lot from the daily temperature. CO2 is also the only source for our foods as foods are produced through the photosynthesis of plants, which converts solar light energy into chemical energy in the form of covalent bonds centered by carbon. Another benefit of CO2 is O2, which is vital for living organisms and is also produced through photosynthesis using CO2.

    As such, CO2 is not the devil. Rather, we have to thank CO2. The problem is that more CO2 than necessary is emitted through fossil fuel burning. We know the ideal answer is to reduce CO2 emissions. However, this is literally just ideal. If we stop using fossil fuels right now, the world’s economy will also stop. You might say that there are alternative energy sources. Yes, you are right. Using alternative and renewable energy sources will reduce CO2 emissions. However, even if we realize carbon neutrality, the CO2 that has already been released will remain in the atmosphere and continue to cause climate change for hundreds of years. So what could be a realistic strategy? We can capture CO2 from the atmosphere and store CO2 deep underground where CO2 came from through “Geotechnical engineering”. However, this technology is not cost-effective and may cause problems such as ocean contamination and earthquakes. Isn’t there any alternative? Yes, there is! That is photosynthesis, which is an inexpensive and safe way to capture CO2.

     As mentioned earlier, photosynthesis is a natural process and thus we do not need to spend money. What we have to do is only minimize organic matter loss from the soils while maximizing organic matter return to the soils. The CO2 entrapped in the organic matter can be stored in the soils through physical-chemical-biological stabilization processes mediated by nature. We call this “soil carbon sequestration”. Atmospheric CO2 concentration should decrease as much as carbon stored in the soils. However, we have to recognize that conventional agricultural practices to produce foods are not suitable for soil carbon sequestration. Lots of carbon is lost during cultivation, particularly through soil disturbance. During the COVID-19 pandemic, global emission of CO2 from fossil fuel combustion decreased; however, unexpectedly, atmospheric CO2 concentration increased probably due to CO2 emission from soils. This indicates that soil can be either the source or the sink of CO2. That is why we need to manage soil resources more conservatively for both food production and climate change mitigation.

    Geotechnical engineering may be promising and attractive as it may create added value and job markets. However, there is no need to use only one means to solve a problem. We need to adopt all possible measures for carbon neutralization to fight against climate change. Soil carbon sequestration should be another solution for carbon neutralization.

By Choi Woo-jung
Professor, Department of Rural and Bio-Systems Engineering
Director, Agri-Bio Institute of Climate Change Management
Leader, Unit for Climate-Smart Reclaimed Tideland Agriculture (BK 21)