Negative and Positive Feedbacks

Geologist, Alasdair Skelton, explains the 3 factors which control Earth’s climate on geological timescales (heat from the Sun, the albedo effect and the greenhouse effect) vary gradually, explaining why Earth was warmer when dinosaurs lived here and why it was cooler during the last glaciation.

That natural climate variations are slow arises because of Earth’s built-in thermostat. This is the very slow weathering of rocks, a chemical process which removes carbon dioxide from the atmosphere. Because this process happens faster when the Earth is warmer and because it cools the Earth by removing the greenhouse gas, carbon dioxide, weathering of rocks stabilizes Earth’s climate. This stabilizing mechanism is called a negative feedback.

Standing on dome-shaped fossils of ancient life called stromatolites, Alasdair Skelton explains that evidence of life on Earth going back 3 billion years confirms that this mechanism has stabilized climate for a very long time.

He also warns of a few exceptions, when this stabilizing mechanism was overwhelmed by other processes, and Earth’s climate destabilized ending in mass extinctions. He points out that one of these exceptions is here and now and we are the cause. By burning fossil fuels, we are releasing far more carbon dioxide to the atmosphere than can be removed by weathering of rocks. This is destabilizing the climate making it warmer.

Warming melts the polar ice caps, making the Earth darker which weakens the albedo effect. This makes the Earth even warmer causing the ice caps to melt faster. This destabilizing mechanism is called a positive feedback.