Over the long term, carbon dioxide has kept temperature relatively stable through the process of chemical weathering.

Question: Examine the weathering feedback cycle below and imagine that a volcanic eruption, emitting a large amount of carbon dioxide, was included as a forcing. How would this feedback cycle respond to eventually stabilize the concentration of atmospheric carbon?

The process is summarized below:

• volcanic eruption increases carbon dioxide concentration
• temperature increases with carbon dioxide concentration, allowing more water vapour to be held in the air
• more water vapour leads to more frequent heavy precipitation events
• heavy precipitation events expose rock which can react with carbon dioxide to form carbonate, removing carbon from the atmosphere
• as carbon dioxide concentrations decline, temperature and water vapour concentrations also decrease
• fewer precipitation events slow the rate of weathering

In the climate system, there are many positive feedback loops which, if triggered, could amplify global warming. Chemical weathering allows life on earth to exist by providing a consistent negative feedback effect.

Question: What would occur if Earth did not have a long term negative feedback to combat the climate changing amplification of positive feedback loops in the climate system?

If there were no overarching negative feedback in the climate system, positive feedback would eventually increase atmospheric temperature to water's boiling point and the earth's oceans would boil away. The water vapour added from the boiling oceans would further amplify the temperature increase, leading to an irreparable, inhospitable climate state. It is believed that a process similar to this occurred on Venus. Open the Planetary Climates learning tool and use the "Planetary data" button in the top left corner to locate Venus on the table and explore this planet's climate. It is fortunate we do not have to worry about this occurring on Earth!