Tipping Points

Causes of Tipping Points

The major causes of tipping points are positive feedback mechanisms related to climate change. Any addition of greenhouse gases to the atmosphere or reduction in the Earth's ability to absorb these gases will increase temperatures and amplify the effect. Reduction in infrared radiation reflection like loss in albedo or cloud cover will amplify changes to climatic conditions.

Tipping Point Examples

Here are some examples of climatic and ecological tipping points:

• Melting sea ice: retreating Arctic and Antarctic glaciers may not be able to recover once temperatures are too high.

• Slowing ocean currents: freshwater from melting ice sheets will slow currents down, so these tipping points are intrinsically linked.

• Permafrost: greenhouse gases released from decomposition in permafrost cause further warming and further melting of permafrost.

• Albedo loss: we depend on Arctic ice sheets to reflect IR radiation back into space (albedo effect), so with less ice the planet will have less albedo and global warming will be exacerbated.

• Producers: reduction in producers from deforestation and climate change reduces the carbon dioxide absorption rate of the Earth, so there will be more greenhouse gases in the atmosphere.

• Carbon dioxide: atmospheric carbon dioxide can only keep increasing to a point. Global temperatures will rise too high and a host of climatic conditions will be unable to recover.

Tipping Points in the Climate System

The climate system is constantly changing because of the natural internal variability of the Earth's system. With the help of palaeoclimatology records, climate researchers have found that the Earth has passed these tipping points on many occasions and undergone many millennia covered in thick ice. However, although many points to the current climate crisis being a result of natural variation, human activity has caused an unprecedented rise in temperatures not seen in 2000 years worth of records.

Over the last 150 years, increased greenhouse gas emissions have been blamed for rising global temperatures, with the huge amounts of fossil fuels being burned for human development being the major culprit (carbon dioxide contributes to 60% of human emissions).

Elements of Tipping Points in the Climate System

These dangerously high temperatures result in various climatic elements being close to their tipping point. These elements include melting sea ice, changing ocean currents, permafrost, and albedo. All of these elements are at risk because they are influenced by dangerous positive feedbacks that amplify climate change's effects.

Polar Sea Ice

Warming air temperatures are causing water molecules to expand in the ocean, meaning that sea levels are rising. Ice sheets around the world are melting from the high temperatures and are now under threat of being engulfed by rising seas. Positive feedback mechanisms are working in all directions here, with increasing temperatures resulting in rising sea levels and melting ice, which both cause an increase in the other!

Thermohaline Circulation Slowing

Analysis of ice cores and ocean sediments has shown the Atlantic Meridional Overturning Circulation (AMOC), which is the Atlantic component of the global conveyor belt, to be moving at its slowest rate for over 1000 years. The slowing of these important ocean currents is caused by melting ice caps, which add freshwater (low in salt content) to the seawater, meaning the colder, saltier regions sink at a slower rate. Decelerating AMOC will have severe implications for tropical regions receiving less cold water to cool the climate and reduce the speed of upwelling regions replenishing nutrients for aquatic ecosystems.

Permafrost

Permafrost is organic matter trapped inside ice mixed with gravel, rock, and soil and is a major concern for climate change. When permafrost is thawed, the organic matter within becomes available to saprotrophic decomposers to break down. In anaerobic conditions, methane will be released from decomposition, while carbon dioxide will be released in aerobic conditions. Methane has a roughly 300x larger greenhouse effect than carbon dioxide in the atmosphere, so large emissions are very dangerous. Permafrost is often found in extreme conditions, so the absence of oxygen is likely.

Decreasing Albedo

Arctic frost plays a significant role in reflecting infrared radiation back into space because of its strong albedo effect. However, with increasing temperatures and rising sea levels, Arctic ice is melting at a rapid rate. There are many positive feedbacks in this situation, too: less reflection of IR rays will cause higher global temperatures, meaning higher sea levels, more melting ice, and even less albedo from Arctic frost.

Global Producers

Worldwide deforestation of arboreal areas is reducing one of the few natural methods we have of absorbing atmospheric carbon dioxide. We depend on the photosynthetic qualities to take up carbon dioxide and release oxygen; reducing atmospheric greenhouse gas content and oxygenating the planet! The deforestation of these areas not only reduces the planets ability to uptake carbon dioxide, but also releases huge amounts of CO² from the combustion of trees.

Tipping Points in Ecosystems

Tipping points are apparent in ecosystems too. The effects of global warming can have lasting effects on ecosystems by destroying habitats and causing certain species to migrate to cooler regions. Human activity has severe impacts on ecosystems as well, with pollution and habitat fragmentation being serious problems. Still, these effects are only called tipping points when they cause irreparable damage (like deforestation).

Elements of Tipping Points in Ecosystems

Let's have a look at some specific examples of potential tipping points in ecosystems. These threats involve positive feedback mechanisms which emphasise the change.

Rainforests

In addition to the loss of a huge source of carbon absorbers which reside in tropical rainforests, deforestation will massively reduce biodiversity in these areas. Ecosystems may struggle to adapt to changing landscapes and drier weather conditions. Certain species may depend on each other (especially those exhibiting symbioses), and food sources will deplete. Habitat fragmentation from large-scale human development will isolate populations causing some species' numbers to dwindle.

Fig. 2: Deforestation in New Zealand. Source: Wikimedia Commons

Coral Reefs

As a result of the exponential increase in carbon dioxide emissions since the Industrial Revolution, we are witnessing unparalleled levels of atmospheric CO². There is extremely high confidence that rising CO² levels affect ocean chemistry; an estimated third of atmospheric CO² is dissolved into the ocean triggering ocean acidification. Dissolved CO² will form carbonic acid and dissociate to form bicarbonate and a proton, which reacts with carbonate molecules producing bicarbonates, lowering the ocean’s carbonate concentration. Calcifying organisms (e.g. coral polyps, crustaceans, echinoderms) depend on carbonate availability to build up their calcareous exoskeletons.

Kelp Forests

Kelp forests are found worldwide and contain dense, biodiverse algal communities that provide food for many marine organisms and form complex ecosystems in these areas. However, warming and pollution can lead to the introduction of epiphytes that grow on and suffocate the kelp. Algal populations with limited provisioning services (called turf algae) begin to dominate in these situations, with these changes affecting food availability for the entire ecosystem. Turf algae populations expand quickly, establishing a feedback loop to resist kelp regrowth.

Peatland

Peat bogs are fantastic sites of carbon sequestration; without them, there would be a catastrophic increase in atmospheric carbon dioxide. These specialised, low-nutrient environments are susceptible to changes in temperature and nutrient content (e.g. from pollution) so they are at risk. Because of the huge amounts of CO² that would be released if peat bogs are damaged, there is a potentially monumental positive feedback mechanism which would incur with the ensuing increase in global temperatures.

Fig. 3: Peatland in Sutherland, Scotland. Source: Wikimedia Commons