Plants do it all the time: it’s called photosynthesis . They take in CO2 from the air, combine it with water, and use it to grow and produce oxygen . Could we build a machine to suck CO2 from the air?
Some engineers are doing just that [e.g. 2,3,4,5,6]! They call it ‘Direct Air Capture’ (DAC) . One company  claims that they will be able to do it for $94-232 per ton of CO2 . Being optimistic and assuming $100 per ton, it would cost $3.7 trillion to remove the amount of CO2 that humans emitted in 2018 (about 37 billion tons ). That’s about 4% of global GDP . Clearly we need to get the price down [8,18].
There are a few different methods of DAC . We will explain the most mature one in simple terms: air is blown across a material that CO2 sticks to, whilst the rest of the air is blown out . The CO2 is then collected and the material is re-used to capture the next load of CO2 . Swipe for a diagram of the chemical reactions!
There are a few challenges [9,18]. For example, capturing CO2 from the air is inherently difficult because the concentration of CO2 is so low: only 400 out of every 1,000,000 molecules in the air are CO2 . This means making the process cost-efficient is difficult .
Scientists and engineers have solved problems in the past that seemed previously unsolvable (electricity , the structure of DNA , the internet  etc.). A recent investment of $68 million into a DAC company , and partnerships between oil companies and teams working on DAC  suggests that people think this technology is promising. This is a sign that DAC will hopefully become more efficient and affordable, and could play a major role in reducing CO2 emissions . However, some scientists argue that other methods of CO2 removal deserve more attention [18,19].
 https://www.sciencedirect.com/science/article/pii/S1876610211003900 See: Abstract
 https://www.nature.com/articles/s41467-019-10842-5 See: Discussion
 https://www.ipcc.ch/site/assets/uploads/sites/2/2019/02/SR15_Chapter2_Low_Res.pdf See: 18.104.22.168 CDR technologies and deployment levels in 1.5°C pathways
 https://www.sciencedirect.com/science/article/pii/S2542435118302253 - diagram inspired by this
 https://pubs.rsc.org/en/content/articlehtml/2018/ee/c7ee02342a See: 12.2 Direct air capture of CO2
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