Direct Air Capture (DAC)
Direct air capture uses technologies that remove CO2 from the atmosphere, thereby extracting carbon previously emitted into the atmosphere by industrial processes, forest fires, etc...
1.5oC 2.7oF
In order to limit global warming to
1.5oC 2.7oF
above preindustrial temperatures, reducing greenhouse gas emissions alone is insufficient. Despite transitions towards lower emissions already underway, few are consistent with limiting warming sufficiently. Carbon dioxide removal (CDR) from the atmosphere will also be necessary.[1]
  • A time-proven, cheap and effective method for extracting CO2 is to plant trees!
  • Various techniques are being developed to extract carbon directly from the atmosphere. This process is known as direct air capture (DAC). Some are described on this page but most are, as yet, unproven and expensive.

Reference:

[1] What Transitions could Enable Limiting Global Warming to 1.5°C? (Accessed on 5th November, 2023) https://www.ipcc.ch/sr15/faq/faq-chapter-4/
$100/ton
$100/ton is the Holy Grail of carbon pricing and startup Graphyte [1] claims to reach that with its carbon-casting technique. Graphyte has backing from Bill Gates' Breakthrough Energy Ventures.
carbon casting blocks
  • Plant residues from timber and farming operations are frequently left to decompose, thereby releasing their stored CO2 into the atmosphere and contributing the climate change. Carbon-casting aims to curtail that release. Graphyte claims to remove carbon from the atmosphere but it might be more accurate to claim that it is reducing the release of carbon into the atmosphere.
  • Graphyte takes waste biomass (discarded wood residue, rice hulls, ...), dries and sterilizes it to prevent decomposition, condenses the material into dense carbon blocks which are then wrapped in a polymer barrier and stored underground. More or less indefinitely [2].
  • This process uses about one-tenth of the energy that most direct air capture methods require. The company is building its first plant in Arkansas, close to timber and rice mills for source materials. It projects to have the capacity to store 50,000 tons per year by July 2024.

References:

[1] Graphyte (Accessed on 20th November, 2023) https://www.graphyte.com/
[2] Bill Gates-Backed Startup to Use Old Wood to Remove Carbon From the Air (Accessed on 20th November, 2023) https://www.bloomberg.com/news/articles/2023-11-13/bill-gate . . .
728 kg/ha 650 lb/ac
Glacial rock flour (GRF) is produced (about one billion tonnes annually) by the glacial erosion - or 'grinding' - of rocks beneath the Greenland ice sheet. This GRF can then be spread on fields where it increases crop yields. It can also absorb
728 kg/ha 650 lb/ac
of CO2 from the atmosphere over a period of three years.[1]
  • The estimated
    728 kg/ha 650 lb/ac
    CO2 results from the application of
    50 tonnes/ha 20 tons/ac
    of Greenlandic glacial rock flour to acidic sandy soil in Denmark. This uses a process known as enhanced rock weathering (ERW).
  • In tests held in Denmark in 2019,
    10 and 50 tonnes/ha 4.1 and 20.3 ton/ac
    of GRF were applied to fields planted with crops of maize and potato. Maize yields increased by 24% and potato yields by 19% for the year of application of GRF. No yield improvements were noted in subsequent years although carbon sequestration continued. [2]

References:

[1] 'Quantification of CO2 uptake by enhanced weathering of silicate minerals applied to acidic soils.' (Accessed on 8th November, 2023) https://www.sciencedirect.com/science/article/pii/S175058362 . . .
[2] Greenlandic glacial rock flour improves crop yield in organic agricultural production (Accessed on 8th November, 2023) https://link.springer.com/article/10.1007/s10705-023-10274-0
4,000 tonnes 3900 (long) tons
In September, 2021, Climeworks launched the world's first direct air capture plant in Hellisheidi, Iceland. This plant (named Orca) has an annual CO2 capture of up to
4,000 tonnes 3900 (long) tons
[1]
  • The plant uses fans to draw air through filters which collect the CO2. When the filter is full, the temperature is raised, releasing concentrated CO2 which is then captured, mixed with water and injected underground where it turns to rock in a couple of years.
  • Iceland has abundant clean geothermal fuel so there is no CO2 associated with powering and heating the plant.
  • The plant cost between $10 million and $15 million to build and captures the emissions of approximately 250 US residents. Individuals can purchase carbon offsets for around $1200/ton. Bulk purchases are closer to $600/ton. [2]
  • Global CO2 emissions for 2022 were
    37.1bn tonnes 36.5 (long) tons
    [3] That works out to be
    1180 tonnes/sec 1160 (long) tons/sec
    (37.1x109/365/24/60/60/60). Each year, the Orca plant will remove slightly less than 3.5 seconds worth of current CO2 emissions.

References:

[1] 'From vision to reality: Orca is launched.' (Accessed on 8th November, 2023) https://climeworks.com/plant-orca
[2] 'World’s Largest Carbon-Sucking Plant Starts Making Tiny Dent in Emissions' (Accessed on 8th November, 2023) https://www.bloomberg.com/news/features/2021-09-08/inside-th . . .
[3] 'Global CO2 emissions from fossil fuels' (Accessed on 8th November, 2023) https://ourworldindata.org/co2-emissions#global-co2-emission . . .