Climate Change Feedback

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.

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.

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.

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.

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).

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.

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.

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.