Our planet is constantly fighting the effects of climate change with essential feedback mechanisms, Earth is doing its very best to survive the onslaught of modern climate change. Human activity releases massive amounts of greenhouse gases into the atmosphere, contributing to the greenhouse effect and warming the Earth’s system. Global warming negatively impacts the different aspects of the environment, resulting in rising sea levels, melting ice caps, and increasingly frequent extreme weather events. The Earth’s system will react to the effects of climate change in various ways; these phenomena are called climate feedback loops.
We will study what the meaning of climate change feedback loop is, the methods of feedback loops, which include climate change positive feedback loops and negative feedback loops, as well as some examples for both mechanisms.
Meaning of Climate Change Feedback Loop
Climate feedback loops are mechanisms by which the Earth’s system reacts to changes in climatic conditions (e.g. temperature, precipitation, cloudiness) to either amplify these conditions (positive feedback loop) or minimise these conditions (negative feedback loop). These feedbacks are a response to climate forcings.
Climate forcings are factors which influence the Earth's climate. These can be internal or external.
Examples of climate forcings are:
- Internal forcings (volcanic activity and ocean circulation).
- Natural external forcings (solar and orbital cycles).
- Anthropogenic external forcings (greenhouse gases, aerosols).
Climate change feedback loop methods
Earth's feedback methods or mechanisms in response to climate change can be broadly grouped in two categories:
- Positive feedback loop: positive feedback mechanisms will respond to a changing climatic condition in a way that emphasises the change. Examples are evaporation of water vapour, the release of methane from permafrost, and rising sea levels.
- Negative feedback loop: negative feedback mechanisms are essential in limiting the effects of climate change. They will respond to changes in a climatic condition by causing a secondary change which limits the impact of the initial change. For instance, increased cloud formation results in more infrared radiation being reflected from these clouds.
Examples of Climate Change Feedback Loop
Let's have a look at some real-life examples of climate change feedback loops so we can understand the environmental drivers behind them.
Examples of positive feedback loops are the ones induced by water vapour, albedo loss, reduced condensation, greenhouse gas emissions from permafrost, changing ocean currents, sea level rising and forest fires. Examples of negative feedback loops include cloud formation, photosynthetic producers, increasing ocean solubility and the Stefan Botzmann Law.
Climate Change Positive Feedback Loops
Climate change positive feedback loops are extremely concerning as they emphasise the adverse effects of climate change, despite sounding encouraging. Let’s have a look at some of Earth’s positive feedback mechanisms:
Water Vapour
Water vapour has the most significant greenhouse gas effect, representing 95% of all greenhouse gases. Rising global temperatures resulting from natural decadal variability and human emissions (contributing to the greenhouse effect) cause more water to be evaporated from the oceans. This water vapour will form in the atmosphere and strengthen the atmosphere’s greenhouse effect, reinforcing the initial impact of climate forcings. Additionally, atmospheric water vapour is less likely to condense and form clouds at higher temperatures.
Greenhouse gases reflect infrared radiation re-emitted from the Earth's surface back towards the Earth (the greenhouse effect) and cause global warming.
Figure 1 : diagram of the greenhouse effect, a climate change positive feedback loop.
Albedo loss
Increasing global temperatures from human greenhouse gas emissions in the last 150 years are causing ice to melt in polar regions. This will release masses of water into the sea and reduce ice cover in cold locations. Ice has a high Albedo effect and reflects 90% of solar radiation. Water, on the other hand, reflects solar radiation poorly. So a reduction in ice cover will reduce the total solar radiation reflected by the Earth, meaning more will be absorbed, and the Earth will warm even further. This is called the Arctic Amplification.
The Albedo effect concerns the ability of a surface to reflect solar radiation. Light surfaces reflect solar radiation much more efficiently than dark surfaces.
Reduced Condensation
Despite rising global temperatures resulting in increased cloud formation and exhibiting promising negative feedback, there is a positive feedback mechanism that counteracts this. Increasing atmospheric temperature will reduce the likelihood of water vapour condensing and forming clouds. Clouds reflect solar radiation back into space, so they help cool the planet. It must also be mentioned that low, thick clouds are the greatest reflectors of solar radiation, whereas high, wispy clouds do not reflect that well. A warmer atmosphere will result in water vapour only being able to condense in the colder, upper sections of the atmosphere and forming clouds that do not reflect radiation well.
You may think that air gets warmer higher up in the atmosphere because it is closer to the sun, but the air pressure is such that low air particles will collide much less frequently, so kinetic energy will be low. Kinetic energy is the energy an object possesses because of its motion, so in the case of air particles, it is their collision rate which determines their kinetic energy.
Greenhouse Gas Emissions from Permafrost
Permafrost thawing is one of the most disconcerting positive feedbacks to climate change because we have limited knowledge of the phenomena, and it has the potential to release massive amounts of methane into the atmosphere. Methane is a highly potent greenhouse gas (100 times more potent than carbon dioxide), so methane release must be restricted at all costs. Permafrost covers 24% of the Northern Hemisphere. When permafrost thaws, the organic matter trapped within becomes available for decomposition by saprobiontic bacteria. In oxygenated conditions, carbon dioxide will be released, but methane will be released in anoxic conditions. These greenhouse gases will reinforce the climatic change which initially occurs (increased global temperature via the greenhouse effect).
Permafrost, or permanent frost, is a mixture of sediment, soil, organic matter and ice which has remained frozen for at least 2 years.
Anoxic means in the absence of oxygen, and is a term you should be comfortable with.
Changing Ocean Currents
Increasing global temperatures negatively impact marine ecosystems by bleaching corals, which has ramifications for intrinsically linked ecosystems (mangroves, seagrass) and the deluge of organisms which rely on these ecosystems for food and shelter. Melting ice resulting from global warming will cause masses of cold, dense water to cascade into the sea, interfering with cold water's descent in Arctic downwelling regions. These downwelling currents are essential in global nutrient distribution; hence marine producers will receive their nutrients at a slower rate. This will have consequences for the entire ecosystem, amplifying the original effect of climate change.
Downwelling is the sinking of cold, salty, and dense water which is then replaced by warmer, less dense water forming horizontal surface currents from the tropics to the poles and deepwater currents in the opposite direction.
Sea Level Rising
Rising sea levels stemming from increasing global temperatures are caused by melting ice and the expansion of heated water. There is positive feedback in rising oceans, though, as elevated seas may engulf coastal ice in other locations causing sea levels to rise even further.
Forest Fires
Tropical regions witness the highest temperatures from global warming and are vulnerable to heatwaves' effects. Forest fires are a particular issue, as many trees undergo combustion, releasing carbon dioxide into the atmosphere. Trees are photosynthetic producers, so their loss will reduce the Earth's ability to uptake carbon dioxide. This will reinforce the original change: the influx of greenhouse gases into the atmosphere.
Figure 2: wildfire in Bitteroot National Forest, Montana via Wikimedia Commons
Climate Change Negative Feedback Loops
Climate change negative feedback loops are unique mechanisms that counteract climate change's impacts. They involve the Earth responding to changes in climatic conditions by shifting another climatic condition to a state which negates the initial change. That may sound confusing, so here are some examples of negative feedback mechanisms:
Cloud Formation
Escalating global temperatures combined with melting ice caps, ocean water evaporation is constantly increasing. More evaporation increases the potential for atmospheric cloud formation. Clouds contribute to the reflection of solar radiation back into space; therefore, increased cloud cover will cool the Earth's temperature, reducing the effects of the initial change.
Photosynthetic Producers
Higher atmospheric carbon dioxide levels from human activities result in an initial increase in plant growth, as plants require carbon dioxide for photosynthesis. Producers offer a negative feedback to global warming by reducing the greenhouse effect. Despite being encouraging, carbon dioxide will only increase rates of photosynthesis up to a certain point before it becomes a limiting factor, as plants require water, light intensity and nutrients as well.
Warming-induced positive feedbacks reduce the effects of negative feedback. For example, warming causes the replacement of fast decomposing plant matter with lower-quality, slow decomposing plant matter, which reduces the amount of carbon dioxide released into the atmosphere. This will simultaneously increase decomposition rates and release more carbon dioxide into the atmosphere.
Increasing Ocean Solubility
The rising sea levels caused by warmer temperatures (and ice caps melting) will result in the oceans holding a greater volume of water. Larger oceans will be able to absorb greater quantities of carbon dioxide from the atmosphere, minimising the original effect of greenhouse gases being emitted into the atmosphere. Although promising, ocean acidification has severe ramifications for marine wildlife that require carbonates to build up their shells and exoskeletons.
The Stefan Boltzmann Law
The Earth's surface is one of the most significant contributors to the re-emission of solar radiation back into space. The warmer the Earth's surface, the more radiation it will emit into space. Therefore, global warming will cause the Earth to emit more infrared radiation into space, cooling down the planet in the process and reducing global warming.
Climate change Feedback mechanisms - Key takeaways
Climate feedback loops are mechanisms by which the Earth reacts to changes in climatic conditions; this reaction will either reinforce or minimise these changes.
Climate forcings are factors which influence the Earth's climate.
Examples of climate forcings are:
- Internal forcings (volcanic activity and ocean circulation).
- Natural external forcings (solar and orbital cycles).
- Anthropogenic external forcings (greenhouse gases, aerosols).
Positive feedback loops involve the amplification of the original climatic change (e.g. evaporation, loss of ice albedo)
Negative feedback loops help to limit the effects of climate change by reacting to a change in a climatic condition by causing a shift in another condition, which reduces the initial change.
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