Climate change feedbacks

Climate change feedbacks are effects of global warming that amplify or diminish the effect of forces that initially cause the warming. Positive feedbacks enhance global warming while negative feedbacks weaken it.^: 2233 Feedbacks are important in the understanding of climate change because they play an important part in determining the sensitivity of the climate to warming forces. Climate forcings and feedbacks together determine how much and how fast the climate changes. Large positive feedbacks can lead to tipping points—abrupt or irreversible changes in the climate system—depending upon the rate and magnitude of the climate change.

The main positive feedback is that warming increases the amount of atmospheric water vapor, which is a powerful greenhouse gas. Another positive feedback is the loss of reflective snow and ice cover. Positive carbon cycle feedbacks occur when organic matter burns or decays, releasing CO₂ back into the atmosphere. Loss of organic matter can happen through rainforest drying, forest fires, and desertification. Methane can also be released into the atmosphere by thawing permafrost.

The main cooling effect is called the Planck response, which comes from the Stefan–Boltzmann law. It states that the total energy radiated per unit surface area per unit time is directly proportional to the fourth power of the black body's temperature. The carbon cycle acts a negative feedback as it absorbs more than half of CO₂ emissions every year. Atmospheric CO₂ gets absorbed into rocks, absorbed into plants, and dissolved in the ocean (leading to ocean acidification).

Accounting for all feedbacks requires considering physical feedbacks, biological feedbacks and carbon cycle feedbacks. Different results can be produced depending on time frame and location. Carbon cycle feedbacks are negative as carbon uptake increases when atmospheric concentrations increase, but warming temperatures and saturation of carbon sinks will decrease that effect. Overall feedbacks are expected to trend in a positive direction over the near future, but the Planck response will become increasingly negative as the planet warms.^: 94–95 There is no threat of a runaway greenhouse effect from current climate change.