CO₂

CO₂ is a colorless gas…

• condenses into solid form (dry ice) at -78°C in atmospheric pressure.
• condenses into liquid at -57°C at pressure above 5.1 atmospheric pressure.

Atmospheric CO₂ is derived from (The sources …)

• Volcanic outgassing
• burning of organic matter
• Respiration of living organisms
• …

CO₂ can be stored in (The Sinks …)

• Highly soluble in water: forms H₂CO₃
• Dissolved CO₂ in water can interact with silicate minerals to form carbonated minerals…
• …

Carbon Dioxide Cycle

The mechanism by which Earth self-regulates its temperature is called the carbon dioxide cycle , or the CO₂ cycle for short.

Starting with the carbon dioxide in the atmosphere:

• Volcanoes outgas CO₂ into the atmosphere.
  
• Atmospheric carbon dioxide dissolves in the oceans.
  
• At the same time, rainfall erodes rocks on Earth's continents and rivers carry the eroded minerals to the oceans.
  
• In the oceans, the eroded minerals combine with dissolved carbon dioxide and fall to the ocean floor, making carbonate rocks such as limestone.
  
• Over millions of years, the conveyor belt of plate tectonics carries the carbonate rocks to subduction zones, and subduction carries them down into the mantle.
  
• As they are pushed deeper into the mantle, some of the subducted carbonate rock melts and releases its carbon dioxide, which then outgasses back into the atmosphere through volcanoes.

The CO₂ Cycle

The CO₂ cycle acts as a thermostat that regulates the temperature of the Earth…

If Earth warms up a bit, then carbonate minerals form in the oceans at a higher rate. The rate at which the oceans dissolve CO2 gas increases, pulling CO2 out of the atmosphere. The reduced atmospheric CO2 concentration leads to a weakened greenhouse effect that counteracts the initial warming and cools the planet back down. If Earth cools a bit, carbonate minerals form more slowly in the oceans. The rate at which the oceans dissolve CO2 gas decreases, allowing the CO2 released by volcanism to build back up in the atmosphere. The increased CO2 concentration strengthens the greenhouse effect and warms the planet back up