The word equilibrium might make you think about chemistry however equilibrium is more than just balanced equations. Our planet is made up of many equilibria and the increasingly concerning effects of global warming are causing them to hang by a thread. Climatic conditions like temperature, precipitation, and storm severity are reaching alarming levels, endangering the world's environment and ecosystems, as well as human populations. Today we are going to go over some of the potential tipping points which could wreak havoc on the Earth in the foreseeable future.
Tipping Points: Definition
Tipping points describe the point of no return in different environmental and ecological conditions. This means that small additional changes could lead to irreversible consequences for human populations, ecosystems, and the climate system as a whole. Positive feedback mechanisms are involved in the tipping point theory; when a certain threshold is reached the amplifying effects of positive feedbacks will be too strong for the condition ever to return to normal.
Tipping points refer to a point at which further changes could lead to irreversible consequences.
Positive feedbacks exacerbate an initial effect.
Probably the most important tipping point of them all, the projected 1.5ºC increase in global temperatures by climate scientists (50% chance of happening) is considered a point of no return.
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.
Paleoclimatology is the study of past climates prior to the introduction of global instrumental records. Modern techniques of measuring climatic conditions only date to the 1880s, so climate proxies are important in providing accurate reconstructions of the Earth's climate over the course of history.
Climate proxies are natural ways that the Earth’s climate history has been preserved. Types of climate proxies include ice cores, tree rings, and boreholes.
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).
GHG emissions can be described as having a tipping point themselves. Increasing atmospheric temperatures result in more water vapour forming. Water vapour is a greenhouse gas and even has the most powerful greenhouse effect! Therefore increasing air temperatures from GHG emissions is causing positive feedback mechanisms involving water vapour.
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!
Worldwide, sea levels are rising 3.3 millimeters a year, which is 30% faster than they were when rising sea levels were first recorded by satellites in 1992!
Tipping points have been projected in the Amundsen Sea embayment of West Antarctica showing that the collapse of ice sheet structure in this area could devastate square kilometres of the West Antarctic ice sheet. The melting of the Greenland ice sheet could have similarly catastrophic effects and has been predicted to cause a 7m increase in sea levels!
An embayment is an indentation in a coastline that forms a bay.
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.
Thermohaline circulation involves the descent of colder, saltier (dense) water and the replacement of this water with warmer, less salty (less dense) water. The pulling forces from this replacing water will create a series of the horizontal surface and deep-water currents, as well as upwelling and downwelling regions.
The result of thermohaline circulation is the global conveyor belt. This is a network of surface, deep water, downwelling, and upwelling currents around the world which brings warm surface water from the tropics to the poles and deep cold water from the poles to the tropics. The GCB heavily influences the climate in these areas.
Fig. 1: The global conveyor belt and the effects of thermohaline circulation. Source: Wikimedia Commons
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.
The positive feedback here are the greenhouse gases released from permafrost, which warm the atmosphere causing more thawing of permafrost.
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.
The term albedo describes the effectiveness of a surface in reflecting infrared radiation from the sun.
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).
Ecosystem tipping points can also be evolutionary! Isolated populations may undergo speciation and form a different species altogether that may struggle to survive. Evolutionary' arms races' between predator and prey and competitors may lead to the extinction of certain species that struggle to adapt.
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
One-quarter of the Earth's carbon exchange between the biosphere and the atmosphere takes place in the Amazon rainforest!
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
Tipping Points - Key takeaways
- Equilibrium tipping points involve irreparable changes to environmental conditions or ecosystems.
- Positive feedback mechanisms are key here: once the condition reaches a certain threshold, the positive feedback becomes so strong that the effects become irreversible.
- Positive feedback magnifies or exacerbates a process.
- Human emissions and the subsequent global warming are the main causes behind potential tipping points.
- GHG emissions can be described as having a tipping point themselves as increasing atmospheric temperatures result in more water vapour forming and water vapour is a greenhouse gas.
- We are already seeing concerning changes to ecosystems around the world; this could be human populations next!
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