A familiar analogy describes an overflowing bathtub and recommends turning off the tap before mopping the floor. If that wisdom applies to the climate crisis, GhG sources must be turned off before decarbonizing the atmosphere.

The World Resources Institute has compiled ways to reduce — if not turn off — sources of CO₂ and other GhG.^[4]

1. Phase out coal plants
2. Invest in clean energy and efficiency
3. Retrofit and decarbonize buildings
4. Decarbonize cement, steel, and plastics
5. Shift to electric vehicles
6. Increase public transport, biking, and walking
7. Decarbonize aviation and shipping
8. Halt deforestation and restore degraded lands
9. Reduce food loss and waste and improve agricultural processes
10. Eat more plants and less meat

As coal and petroleum power are phased out, abundant energy is available from the sun, wind, and sea

• CARBON SINKS

  Biological carbon sequestration is the natural process where the CO₂ in grassland and forest vegetation forms carbon sinks. As those repositories are preserved and cultivated, more carbon is removed from our atmosphere. A single hectare (2.5 acres) of forest removes up to 33 tons of CO₂ annually.^[5] In forests worldwide, estimated annual sequestration is two gigatons… the weight equivalent to 20,000 U.S. aircraft carriers.

  Grasslands and wetlands store more carbon per acre and more quickly than forests.^[6] The oxygen-poor soil there inhibits CO₂ release.

The biomass beneath salt marshes sequesters more than 1,000 tons of carbon. Soil organic carbon in forests totals less than 1/3 of that.

• FARMLAND

  Whether cultivated or left fallow, strategic use of farm acreage is vital to sequestering carbon.

  One strategy involves adding organic materials to the soil. Another is the cultivation of longer-rooted crops.

  Carbon is also sequestered when land is set aside and remains uncultivated.

The Farm Service Agency pays rent for acreage that farmers reserve for grasslands, wetlands, and forests.

• BIOENERGY WITH CARBON CAPTURE AND STORAGE (BECCS)

  Each year, BECCS stores an estimated 0.3 billion tons of atmospheric carbon as river and ocean sediment. It’s a natural process!

  Carbon capture begins when rainwater dissolves CO₂in the atmosphere. This produces carbonic acid, which — in rainwater — slowly dissolves rocks. Rivers transport the dissolved, carbon-laden material into the oceans, where it may remain as sediment for thousands of years.^[7]

  To boost the natural process, crushed rock can be spread over extensive areas of land or water. That increases the surface area where the natural process occurs. Also, crushed rocks can be exposed to CO₂ in a reaction chamber. That industrial process yields results similar to natural chemical weathering.

At mining sites like these, every rainy day brings chemical weathering as carbonic acid in rainwater interacts with the scattered rocks.

• INDUSTRIAL CCS

  The CO₂ emissions released during power generation, steelmaking, or cement production can be captured through decarbonization. That process has taken many forms since being first patented in 1915.^[8]

  Industrial CCS can be stabilized in concrete or plastic. Some may be further processed into graphene for smartphone screens and other tech devices. It also can be injected into saline aquafers — underground expanses of porous, sedimentary rock filled with salt water.

Germany implemented CCS processes at a coal-fired plant in 2008.^[9]

CO₂ mixes evenly throughout the atmosphere, but the air is denser near ground level. That means CO₂ concentrations are greatest in the troposphere, the first 10 kilometers above ground level.

Devices for scrubbing CO₂ from breathable air have already been deployed on submarines and in space vehicles. Those will not scale large enough to cleanse the atmosphere. Research continues at the Arizona State University (ASU) Center for Negative Carbon Emissions and in university, government, and corporate laboratories worldwide.

Today’s industrial facilities have a combined global capacity to capture 40 million tons of CO₂. That’s less than 1% of the amount industry produces.

A candidate technology from Carbon Engineering, Ltd. would deploy semi-trailer-sized boxes filled with a material that absorbs CO₂ 1,000 times more efficiently than plants. The material has been laboratory-tested and will soon be demonstrated on a small scale.

This image illustrates a portion of Carbon Engineering’s proposed DAC network. The completed network would capture an estimated 110 million tons of CO₂ daily, costing $30 per ton.

Biochar is approximately 70% carbon. It is the product of torrefaction, the controlled burning of organic waste from forestry and agriculture. The result is lightweight and looks like porous charcoal.

Torrefaction requires the wood chips, leaf litter, dead plants, and other biomass to be burned in a container with very little oxygen. During the process, a few fumes are released. The product, biochar, captures carbon in a stable form that is slow to decompose and cleaner than charcoal.

Less-refined biochar has been spread on farmlands for centuries, enriching the soil. The slow, low-temperature torrefaction process has only recently been devised for carbon sequestration.

After torrefaction (roasting), wood and other biomass have increased carbon density. Decreased weight makes biochar easier to transport and store.

Tree planting is a promising yet painstaking way to capture atmospheric CO₂. Trees are roughly half carbon. They absorb that carbon through photosynthesis, a process which over months and years converts CO₂ to the more stable form of carbon — the wood of a tree’s trunk and roots. Genetic modification aims to accelerate the process!

The relatively inefficient photosynthesis of most trees limits the energy for tree growth. Researchers at one biotech company are genetically-enhancing trees to better absorb atmospheric CO₂. In one 4-month trial, the researchers used bacteria to insert genes from pumpkin and green algae into poplar trees. Those trees proved to be more efficient at recycling carbon, adding 53% more weight than a control group of unmodified poplars.^[10]

The United Nations, through its International Atomic Energy Agency, conducts plant breeding and genetics research in Seibersdorf, Austria.

Feeding phytoplankton may have potential as a fast, low-cost tactic for carbon sequestration. Even so, the potential disruption of fisheries and other ocean ecosystems must not be overlooked. Other concerns include substantial energy requirements that would raise the cost.^[11]

Individual phytoplankton, including single-celled green algae, are less than 2 microns in diameter but have a significant ability to absorb CO₂. In controlled settings, vast numbers of the plantlike organisms could sequester carbon for about two dollars per ton. To grow, they only need water and nutrients that are iron and nitrogen-rich.

CO₂ could be sequestered from High Nutrient, Low Chlorophyll (HNLC) regions in the North Pacific, Equatorial Pacific, and Southern Ocean, where phytoplankton is abundant.^[12] One proposed demonstration would fertilize 5,000 square miles of a Pacific HNLC region. Doing so would sequester an estimated 600,000-2,000,000 tons of CO₂ in just 20 days!

During photosynthesis, phytoplankton absorb CO₂ and release oxygen.

Iconic Liquid (IL) is an uncommon term, but IL has a scientifically-proven ability to capture CO₂ from emissions that would otherwise contribute to global warming.

• • ILs are chemical salts in liquid form.
  • Most of them are colorless and viscous.
  • All of them have polysyllabic names like 1-butyl-3-propylamineimidazolium tetrafluoroborate.

In a CO₂ absorption device, feed gas would pass through columns containing IL that would absorb and strip away all but CO₂-rich gas. That output could then be sequestered.^[13]

BMIM-PF₆ is one of many polysyllabic ILs with proven ability to absorb CO₂.