Radiocarbon in Climate Models

A recent study published in the journal Science investigated the remains of nuclear bomb tests conducted by the U.S. and the Soviet Union in the 1960s for use in climate models.

• The researchers used climate models (Coupled Model Intercomparison Project CMIP) to estimate the amount of carbon stored in vegetation around the planet in a year. 
  • The CMIP models used in the study included some of the latest versions (5 and 6).

Key Highlights of the Study

• The Study: The Researchers used climate models to track the change in the level of Carbon 14 between 1963 and 1967 and thereby estimate the amount of carbon stored in vegetation around the planet in a year. 
  • The Nuclear explosions during the Cold War period sprayed radioactive material around the planet’s atmosphere. 
    • Carbon-14: It is an isotope of carbon also called Radiocarbon. Its atom’s nucleus has two neutrons more than the most common Carbon-12. The nuclear bomb tests steadily deposited  more than usual quantity in the atmosphere.
    • Radiocarbon bonds with oxygen to form CO2
  • Limited Test Ban Treaty (LTBT): With the signing of the LTBT treaty in 1963 prohibiting nuclear testing over land, air, and under water the atmospheric radiocarbon concentration stopped increasing beyond this year.
• Findings: 
  • The models suggested that the radiocarbon was moving into vegetation from the atmosphere as the vegetation absorbed this Radiocarbon converted CO2 during photosynthesis to produce food and energy. 
  • Carbon Hosted in Vegetation: Scientists have used satellite data to estimate how much carbon vegetation around the world hosts by using climate models to estimate the amount of carbon stored in vegetation around the planet in a year. 
    • The study estimates 80 billion tonnes of carbon being stored per year, most of them being stored in leaves and finer roots, i.e. the non-woody parts of the plant as opposed to the previous estimates of  43-76 billion tonnes per year
  • Fast Carbon Recycling: The Carbon Cycling is moving at a speed greater than previously thought as the plants are absorbing more CO2 from the atmosphere and storing  it for a shorter duration than expected, before releasing it into their surroundings.
    • Carbon Cycle: Plants absorb CO2 from the atmosphere during photosynthesis and use it to make glucose. A plant consumes some of the glucose and some it stores as starch in its leaves. In this process, some carbon is also lost when the plant exhales CO2 as it respirates.

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