The world today is on average more than 1.1 degrees warmer than it was in 1850 and counting. According to calculations by the Intergovernmental Panel on Climate Change, it could even be up to three degrees by the end of the century.

The main reason for the rise in temperature is the increase in CO2 in the atmosphere. The greenhouse gas slows down the radiation of heat into space, which is why the earth is warming up. The proportion of CO2 in the air has increased over the past 170 years from 0.029 to 0.041 percent (288 ppm to 414 ppm).

A lot of CO2 is produced by burning coal, oil and gas, as well as by slash-and-burn and in industrialized agriculture. In the last 50 years, more than 1200 billion tons of CO2 have been emitted into the atmosphere worldwide. In 2018 alone it was 36.6 billion tons. As a result, the average global temperature rose by 0.8 degrees in just half a century.

Coal, oil and gas were formed from forests, plankton and other plants over millions of years. These had bound CO2 from the atmosphere when they grew millions of years ago. With the combustion today, this CO2 is released again.

In 2015, the world agreed with the Paris climate agreement to stop global warming to 1.5 degrees if possible and well below two degrees.

In order to achieve this goal, only a small amount of additional CO2 must be released into the air. According to the Intergovernmental Panel on Climate Change, a maximum of around 300 billion tons of CO2 should be emitted worldwide. But if global emissions remain as high as they have been, this CO2 budget will be used up in less than seven years.

Climate scientists assume that negative emissions are also necessary to achieve the climate goals. There are different possibilities for this.

One measure for binding CO2 is the planned reforestation of forests. According to studies, while young trees are growing, around 3.6 billion tons of CO2 could be bound worldwide every year, around 10 percent of current CO2 emissions. Very large areas would be needed for this – in total as much as the area of ​​the entire USA, according to a study by the Swiss Federal Institute of Technology ETH Zurich

Humus contains a lot of carbon. However, due to the industrialization of agriculture, a lot of humus in the soil has been lost in recent years, and the carbon has become CO2. It takes time for new humus to form, but the humus content in the soil can be significantly increased again by cultivating cover crops, deep-rooted plants, incorporating crop residues and avoiding deep plowing.

According to a study by the Stiftung Wissenschaft und Politik (SWP), a global build-up of humus could bind between two and five billion tons of CO2 per year.

Some scientists see biochar as a promising technology for binding CO2. Organic material is artificially charred with the help of heat, pressure and the exclusion of oxygen. In pulverized form, this biochar is then spread on farmland.

There it acts as a fertilizer and also increases the carbon content in the soil. If this technology were used globally, between 0.5 and two billion tons of CO2 could be bound annually.

One method that could bind significantly more CO2 is underground storage of CO2. It is practiced in Norway’s oil fields, for example. However, the process is also controversial because the CO2 in the subsoil can lead to earthquakes and escape in the long term. Another storage method is currently practiced in Iceland. CO2 is bound there with basalt and turned into stone. This connection is stable. Both methods still require research.

Before it can be stored, the CO2 must be extracted from the ambient air using chemical processes. Some of the systems required for this (direct air capture) already exist in Europe. The potential is great, there is no quantity limit.

The downside is currently the cost. The World Resource Institute (WRI) assumes costs of between 250 and 600 US dollars per tonne of CO2, depending on the technology used. Reforestation, on the other hand, costs only about 50 US dollars per tonne of CO2 stored, which is significantly cheaper in comparison.

Some researchers predict that with mass production of carbon capture and storage (CCS) systems, prices could drop to 50 euros per tonne by 2050.

The technology is considered a key technology for climate protection.

Another way of extracting CO2 from the air is via biomass. Crops are grown and burned in the power plant to produce electricity. CO2 is then extracted from the exhaust gas of the power plant and stored deep in the earth.

The big problem with this technology (BECCS) is the immense space requirement. For this reason, many experts are critical of this technique. According to Felix Creutzig from the Mercator Research Institute on global Commons and Climate Change (MCC) in Berlin, it will therefore only play “a small role” among CO2 removal technologies.

In this process, carbonate and silicate rocks are mined, ground and applied to agricultural land or the sea. Over the years, natural processes bind CO2 to this stone dust and it is stored. With this method, the CO2 binding potential from the atmosphere is between two and four billion tons per year. The major challenge with this method is above all the large quantities of ground stone required and the infrastructure required for this. Specific methods have not yet been explored. This article was updated on 12/22.

Author: Gero Rueter

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The original of this post “How can CO2 be removed from the atmosphere?” comes from Deutsche Welle.