Why do we need to capture CO2?

In the previous blog post we learned that Carbon dioxide (CO2), Methane (CH4), Nitrous oxide (N2O), hydrofluorocarbons (HFCs), Perfluorocarbons (PFCs), Sulfur hexafluoride (SF6), Nitrogen trifluoride (NF3), Ozone (O3) and water vapor are collectively known as greenhouse gases and their excessive accumulation in the atmosphere is trapping sun's heat causing global warming. Carbon Dioxide contribution is significant because it can stay longer in the atmosphere [~100 years]. According to NOAA, the annual rate of CO2 increase is 100 times faster than previous natural events such as ice age. In the 1960s, the rate of atmospheric CO2 increase was 0.8 ppm per year. In the 1980s, it became double and remained steady at 1.5 ppm per year in the 1990s. In the 2000’s it increased to 2.0 ppm per year. In the past decade the rate of increase accelerated to 2.4 ppm per year. The latest data shows that measured CO2 concentration in atmosphere is ~421 ppm.

The biggest question in everybody’s mind is who is the major contributor for this increase? When fossil fuels such as coal, oil, and natural gas are burned, they release CO2 into the atmosphere. Fossil fuels are burned every day in power generation plants, transportation, residential and commercial buildings. CO2 is also emitted during certain industrial processes like cement manufacture or hydrogen production and during the combustion of biomass. In addition, deforestation and other land-use changes also contribute to CO2 emissions. Burning fossil fuels and industrial activities have contributed 89% of 2020 emissions and remaining 11% comes from change in land use. It has been shown in figure 1.

Figure 1 – Major CO2 emission contributors (2020 data)

Figure 2 – Annual CO2 emissions by fossil fuels

Figure 3 – Total Anthropogenic CO2 emissions between 2011 and 2021

Figure 2 shows the sharp increase in CO2 emissions due to fossil fuel usage over the years. Figure 3 shows the historical CO2 emissions between 2011-2021. The major contributor of CO2 emissions is still fossil fuels. Considering an annual average of 40 Gt of CO2 is emitted by manmade activities and convert to CO2 concentrations, it will be equal to ~5 ppm. The calculations can be done using the following formula.

2011 atmospheric CO2 concentrations were 395 ppm. ~5 ppm of CO2 addition every year, we would have added more than 60 ppm for the past 12 years. In addition, natural processes such as outgassing from the ocean, decomposing vegetation and other biomass, venting volcanoes, naturally occurring wildfires all contribute to CO2 concentration in the atmosphere. The 2023 data indicates that atmospheric CO2 concentration is ~421 ppm. Something does not add up, right? All the emitted CO2 is not lingering in earth’s atmosphere. As discussed earlier, mother nature has mechanisms in place to absorb the CO2. Soil, Vegetation and Oceans are the largest carbon sinks. Almost 55% of the CO2 emitted is absorbed by the natural carbon sinks. Remaining 45% will account for 2.3 ppm CO2 concentration increase annually which is approximately equivalent to 421 ppm. According to IPCC estimates the global temperature would rise 2oC more than preindustrial levels if we double the CO2 concentration (280 ppm). Although, global warming is a natural process to keep the earth’s temperature above freezing, human activities fast tracked this natural phenomenon to a point it becomes a global crisis.

CO2 emissions from human activities are now the main driver of climate change, and reducing these emissions is crucial for slowing down and eventually reversing the impacts of climate change. There has been plenty of efforts to curb CO2 emissions and as well as reduce the existing concentrations to the levels that earth can tolerate. The discussion in previous paragraphs paint a clear picture that we need to find a way to prevent rise in CO2 concentration in our atmosphere. Eliminating fossil fuel usage will solve our world’s problem. Although the idea is very simple, it is very hard to implement immediately. We don’t have any viable alternative energy options that has comparable energy density as that of fossil fuels or economical for large scale implementation. Renewable energy technologies are slowly replacing the fossil fuels in every sector. However, we can’t achieve full independence from fossil fuels in a foreseeable future.

Over the years, there has been lot of efforts from international community to find ways to reduce CO2 emissions or at least maintain current levels. One of the ideas is to capture the CO2 from the source of emission and store it underground. Some of the storage options are depleted oil and gas wells, salt caverns, ocean beds, conversion of CO2 to a product where it can be permanently tied up for very long time (cements, plastics).