Plants on Earth act like a giant control knob for the amount of carbon dioxide (CO₂) in the atmosphere: they pull CO₂ out of the air and store it, but they also send a lot of it back.

Big idea in one line

Plants reduce the amount of carbon in Earth’s atmosphere by taking in CO₂ during photosynthesis and storing it in their bodies and soils, but they also increase it again when they respire, die, or burn.

Mini-section 1: Photosynthesis – plants as carbon “vacuum cleaners”

When plants photosynthesize, they:

  • Take in carbon dioxide from the air.
  • Use sunlight and water to turn that CO₂ into sugars.
  • Build leaves, wood, roots, and fruits out of those sugars.

In this process, carbon moves:

  • From the atmosphere → into plant biomass (trunks, leaves, roots).
  • This process is called carbon fixation or sequestration , because the carbon is now “locked up” instead of floating in the air as CO₂.

On a global scale, land plants and soils soak up a huge chunk of human CO₂ emissions each year, acting as a carbon sink , which slows down climate change.

Mini-section 2: Respiration – plants also “breathe out” CO₂

Plants are living organisms, so they:

  • Break down some of their stored sugars to get energy.
  • Release CO₂ back into the atmosphere during respiration.

Key points:

  • Roughly, plants return a large fraction of the CO₂ they absorb back to the air through respiration.
  • Warmer temperatures can make plant respiration faster, which can increase the amount of CO₂ they release.

So, plants are both :

  • A sink (they remove CO₂).
  • A source (they release CO₂).

What matters for the atmosphere is the net effect : how much more they take in than they give back.

Mini-section 3: The full carbon cycle – what happens to plant carbon next?

Once carbon has entered a plant, it can follow several paths:

  1. Stored for a long time
    • In wood of trees that live for decades or centuries.
    • In soils, when dead plant material is buried and decomposes slowly.
    • This is long-term carbon storage, which helps keep CO₂ out of the air.
  2. Returned fairly quickly
    • When plants respire.
    • When leaves, roots, or whole plants die and are decomposed by microbes (which release CO₂).
    • When forests or fields burn, turning plant carbon back into CO₂ in a short burst.
  3. Moved through food webs
    • Animals eat plants and take in their carbon.
    • Animals then respire, releasing some carbon back to the air as CO₂.
    • Their waste and bodies eventually decompose, releasing more CO₂.

So plants are the entry point for most carbon that gets into land food webs.

Mini-section 4: Plants and seasonal “breathing” of the planet

If you look at CO₂ measurements over a year, especially in the Northern Hemisphere, you see a pattern:

  • Spring and summer:
    • Plants grow, leaf out, and photosynthesize more.
    • They pull a lot of CO₂ out of the air.
    • Atmospheric CO₂ levels dip.
  • Fall and winter:
    • Leaves fall, growth slows.
    • Decomposition and respiration dominate.
    • CO₂ levels rise again.

It is as if Earth is “breathing” once a year: inhaling CO₂ during the growing season and exhaling it when plants die back.

Mini-section 5: Modern twist – climate change and the plant–carbon balance

Today, the relationship between plants and atmospheric carbon is becoming more complicated:

  • Extra CO₂ can boost plant growth (“CO₂ fertilization”), which can help plants absorb more carbon.
  • But:
    • Heat waves and droughts can kill plants or slow growth.
    • Warmer conditions can increase respiration and decomposition, sending more CO₂ back to the air.
    • Disturbances like wildfires, deforestation, and insect outbreaks release large amounts of stored carbon quickly.

So, although plants currently help by offsetting part of human CO₂ emissions , they cannot cancel them out entirely, and their ability to act as a strong carbon sink may weaken if ecosystems become stressed.

Short, study-ready answer

Plants affect the amount of carbon in Earth’s atmosphere by taking in carbon dioxide during photosynthesis and storing that carbon in their tissues and in soils, which lowers atmospheric CO₂. Over time, they also release carbon back into the atmosphere through respiration, decay, and burning, so the overall impact depends on the balance between how much carbon they absorb and how much they give back.