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A Description of Critical Tipping Points

David Klein

Moderator
These are the tipping points that will push us into climate disaster

These are the tipping points that will push us into climate disaster


Imagine cutting down a tree. Initially, you chop and chop … but not much seems to change. Then suddenly, one stroke of the hatchet frees the trunk from its base and the once distant leaves come crashing down.

It’s an apt metaphor for one of the most alarming aspects of climate change – the existence of “tipping elements.”

These elements are components of the climate that may pass a critical threshold, or “tipping point,” after which a tiny change can completely alter the state of the system. Moving past tipping points may incite catastrophes ranging from widespread drought to overwhelming sea level rise.

Which elements’ critical thresholds should we worry about passing thanks to human-induced climate change?

You can see the answer on this graphic – and find more information below.


Image: EDF
The most immediate and most worrisome threats

  • Disappearance of Arctic Summer Sea Ice – As the Arctic warms, sea ice melts and exposes dark ocean waters that reflect sunlight much less efficiently. This decreased reflectivity causes a reinforcement of Arctic warming, meaning that the transition to a sea-ice free state can occur on the rapid scale of a few decades. Some scientists have suggested that we have already passed this tipping point, predicting that Arctic summers will be ice-free before mid-century.
  • Melting of the Greenland Ice Sheet – The Arctic warming feedback described above may one day render Greenland ice-free. Research predicts that the tipping point for complete melt can occur at a global temperature rise of less than two degrees Celsius – a threshold that may be surpassed by the end of this century. While the full transition to an ice-free Greenland will take at least a few hundred years, its impacts include global sea level rise of up to 20 feet.
  • Disintegration of the West Antarctic Ice Sheet – The bottom of this ice sheet lies beneath sea level, allowing warming ocean waters to slowly eat away at the ice. There is evidence that this tipping point has already been surpassed – possibly as early as 2014. Like the Greenland Ice Sheet, full collapse would require multiple centuries, but it could result in sea level rise of up to 16 feet.
  • Collapse of Coral Reefs – Healthy corals maintain a symbiotic relationship with the algae that provide their primary food source. As oceans warm and become more acidic, these algae are expelled from the corals in an often fatal process called coral bleaching. Research predicts that most of our remaining coral systems will collapseeven before a global temperature rise of two degrees Celsius.
Tipping points in the distant future

  • Disruption of Ocean Circulation Patterns – The Thermohaline Circulation is driven by heavy saltwater sinking in the North Atlantic, but this water is becoming fresher and lighter as glaciers melt in a warming climate. The change in water density may prevent sinking and result in a permanent shutdown of the circulation. Research suggests that weakening of the Thermohaline Circulation is already in progress, but that an abrupt shutdown is unlikely to occur in this century. Some models suggest that these changes may prompt a secondary tipping element in which the subpolar gyre currently located in the Labrador Sea shuts off. Such a change would dramatically increase sea level, especially on the eastern coast of the United States.
  • Release of Marine Methane Hydrates – Large reservoirs of methane located on the ocean floor are stable thanks to their current high pressure-low temperature environment. Warming ocean temperatures threaten the stabilityof these greenhouse gas reservoirs, but the necessary heat transfer would require at least a thousand years to reach sufficient depth, and may be further delayed by developing sea level rise.
  • Ocean Anoxia – If enough phosphorous is released into the oceans – from sources including fertilizers and warming-induced weathering, or the breakdown of rocks –regions of the ocean could become depleted in oxygen. However, this process could require thousands of years to develop.
Potentially disastrous elements, but with considerable uncertainty

  • Dieback of the Amazon Rainforest – Deforestation, lengthening of the dry season, and increased summer temperatures each place stress on rainfall in the Amazon. Should predictions that at least half of the Amazon Rainforest convert to savannah and grasslands materialize, a considerable loss in biodiversity could result. However, the dieback of the Amazon Rainforest ultimately depends on regional land-use management, and on how El Niño will influence future precipitation patterns.
  • Dieback of Boreal Forests– Increased water and heat stress could also lead to a decrease in boreal forest cover by up to half of its current size. Dieback of boreal forests would involve a gradual conversion to open woodlands or grasslands, but complex interactions between tree physiology, permafrost melt, and forest fires renders the likelihood of dieback uncertain.
  • Weakening of the Marine Carbon Pump – One mechanism through which oceanic carbon sequestration takes place is the marine carbon pump, which describes organisms’ consumption of carbon dioxide through biological processes such as photosynthesis or shell building. As ocean temperatures rise, acidification progresses, and oxygen continues to be depleted, these natural systems could be threatened and render the carbon sequestration process less efficient. More research is necessary in order to quantify the timescale and magnitude of these effects.
Tipping elements complicated by competing factors

  • Greening of the Sahara/Sahel – As sea surface temperatures rise in the Northern Hemisphere, rainfall is projected to increase over the Sahara and Sahel. This increased rainfall would serve to expand grassland cover in the region, but is balanced by the cooling effect of human-emitted aerosols in the atmosphere.
  • Chaotic Indian Summer Monsoon – The fate of the Indian Summer Monsoon similarly depends upon a balance of greenhouse gas warming and aerosol cooling, which strengthen and weaken the monsoon, respectively. On the timescale of a year, there is potential for the monsoon to adopt dramatic active and weak phases, the latter resulting in extensive drought.
More research necessary to establish as tipping elements

  • Collapse of Deep Antarctic Ocean Circulation – As in the case of the Thermohaline Circulation, freshening of surface waters in the Southern Ocean due to ice melt may slowly alter deep water convection patterns. However, the gradual warming of the deep ocean encourages this convection to continue.
  • Appearance of Arctic Ozone Hole – Unique clouds that form only in extremely cold conditions currently hover over Antarctica, serving as a surface for certain chemical reactions and facilitating the existence of the ozone hole. As climate change continues to cool the stratosphere, these “ice clouds” could begin formation in the Arctic and allow the development of an Arctic ozone holewithin a year.
  • Aridification of Southwest North America – As global temperatures rise, consequential changes in humidity prompt the expansion of subtropical dry zones and reductions in regional runoff. Models predict that Southwest North America will be particularly affected, as moisture shifts away from the southwest and into the upper Great Plains.
  • Slowdown of the Jet Stream –A narrow and fast moving air current called a jet stream flows across the mid-latitudes of the northern hemisphere. This current separates cold Arctic air from the warmer air of the south and consequentially influences weather in its formation of high and low pressure systems. A slowing of the jet stream has been observed over recent years. Should slowing intensify, weather patterns could persist over several weeks with the potential to develop into extended extreme weather conditions.
  • Melting of the Himalayan Glaciers – Several warming feedbacks render the Himalayan glaciers vulnerable to dramatic melt within this century, though limitations on data availability complicate further study. Dust accumulation on the mountainous glaciers and the continual melt of snow and ice within the region both prompt a decrease in sunlight reflectivity and amplify regional warming.
Gradual, continuous changes

  • More Permanent El Nino State – 90 percent of the extra heat trapped on Earth’s surface by greenhouse gases is absorbed by the oceans. Though still under debate, the most likely consequence of this oceanic heat uptake is a gradual transition to more intense and permanent El Nino/Southern Oscillation (ENSO) conditions, with implications including extensive drought throughout Southeast Asia and beyond.
  • Permafrost Melting – As global temperatures rise and the high latitudes experience amplified warming, melting permafrost gradually releases carbon dioxide and methane into the atmosphere and creates a feedback for even more warming.
  • Tundra Transition to Boreal Forest– Much like the conversion of the Amazon Rainforest and boreal forests to other biomes, tundra environments may transition into forests as temperatures increase. However, this process is more long-term and continuous.
With a range of critical thresholds on the horizon, each tipping element demonstrates the potential implications of allowing climate change to progress unchecked.

As tipping points loom ever closer, the urgency for emissions mitigation escalates in hopes of sustaining the Earth as we know it.

This post was co-authored by Environmental Defence Fund Climate Scientist Ilissa Ocko


 

David J

Member
I have always conflated tipping points with feedback loops, the point where the warming dynamic is beyond human control? For instance, methane release from perma-frost. Is that a separate phenomenon?
 

David Klein

Moderator
"I have always conflated tipping points with feedback loops, the point where the warming dynamic is beyond human control? For instance, methane release from perma-frost. Is that a separate phenomenon?"​

The phenomena of feedbacks and tipping points are related but they are not the same. The notion of a tipping point signifies irreversibility in a certain sense (like a mathematical concept called "hysteresis"), whereas feedbacks (both positive and negative) do not. Below are some excerpts to help explain these notions from my ebook, which may be freely downloaded here.

Climate feedbacks

The current unprecedented rate of greenhouse gas emissions into the atmosphere is the primary driver of climate change on Earth, but because the climate system is complicated, many other factors must also be taken into account. As the planet warms, the climate system responds in many different ways. One important type of response is called a feedback.

For example, as the planet warms, more water evaporates from oceans and lakes. Because the water vapor in the air is also a greenhouse gas, the planet is warmed further by this evaporation, which causes even more evaporation and therefore more warming. is is an example of a positive feedback, positive because the warming is reinforced.

Another example is the ice-albedo feedback. Albedo is a number between zero and one. It measures the fraction of light re ected from a surface. A white colored surface has an albedo that is almost 1, because it re ects most of the incoming incident light. Dark colored surfaces absorb most of the incident light and are heated by that absorbed light. Very little of the light is re ected back, so a dark surface has an albedo that is nearly zero.

You can feel how this works on a sunny day. Stand barefoot on a white sidewalk, and then step onto the black asphalt on the street. It will feel much hotter. The light colored sidewalk has a high albedo because it reflects most of the light and stays cool, but the dark asphalt reflects very little light (that’s why it’s dark!) and instead absorbs the light and turns it into heat, and then also radiates invisible infrared light.

Arctic ice has an albedo even higher than a sidewalk. It reflects sunlight back into space and helps to keep the planet cool. But as the planet warms up from greenhouse gases, ice melts, and the ground or dark sea water underneath absorbs more sunlight and heats the planet. That in turn causes more ice to melt which heats the planet more. This is another example of a positive feedback.

There are other positive feedbacks and also negative feedbacks. For example, as the planet warms evaporation increases, as discussed above, but the moisture in the air can become part of a cloud which reflects incoming sunlight back into space because of its high albedo.

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5. Tipping points

Imagine an egg sitting on a table near the edge. If you nudge the egg a little closer to the end of the table, not much will change. You can easily push it back to its original position and return the “egg-and-table- system” to its previous state.

Imagine now that after several nudges, the egg sits on the table, partly hanging over the edge. If you give it just one more tiny push past this “tipping point,” the egg will teeter over the edge and fall to the floor, making a big mess. The “egg-and-table-system” has been pushed beyond its tipping point, and is in a new state that cannot be returned to its previous condition.

Earth’s climate system also has tipping points. The National Research Council describes the idea this way:

Studies of past climates show that Earth’s climate system does not respond linearly to gradual CO2 forcing, but rather responds by abrupt change as it is driven across climatic thresholds. Modern climate is changing rapidly, and there is a possibility that Earth will soon pass thresholds that will lead to even larger and/or more rapid changes in its environments. Climate system behavior whereby a small change in forcing leads to a large change in the system represents a “tipping phenomenon” and the threshold at which an abrupt change occurs is the “tipping point.” [NRC]​

There have been rapid shifts to Earth’s climate in the past, and the current changes are accelerating past all previous rates of change in Earth’s history. For example, the shift from the last glacial period to the current warmer climate ended about 11,000 years ago. An abrupt transition occurred when 30% of the land surface changed from ice-covered to ice-free in just a few thousand years. Consider that in only a few hundred years, humanity has converted about 43% of the world’s land to agricultural or urban landscapes [Levitan].

There are a variety of possible tipping points. Increases in ocean acidity and rising ocean temperatures might reach a threshold that would precipitate the rapid loss of coral reef ecosystems and massive extinctions. The Amazon rainforest has been subjected to droughts of increasing severity, so much so that for periods of time it has been a source of atmospheric carbon rather than a “sink” that absorbs atmospheric carbon. The rainforest system is in danger of reaching a tipping point that will result in the widespread die-back of the trees and desertification of the region.

Climate records from Siberian caves suggest that 1.5° C (or 2.7° F) of warming would be enough to thaw permafrost, which covers 24% of the land surface of the northern hemisphere, and holds an estimated 17 trillion metric tons of organic carbon. The release of carbon dioxide and methane at this temperature is then a possible tipping point for continuous permafrost to start thawing and releasing vast quantities of greenhouse gases [Vaks].

The Greenland or West Antarctic ice sheets might have already crossed tipping points beyond which they are doomed to shrink and disappear altogether within a few centuries. James Hansen, one of the world’s leading climatologists, warned in 2008,

The warming that has already occurred, the positive feedbacks that have been set in motion, and the additional warming in the pipeline together have brought us to the precipice of a planetary tipping point. We are at the tipping point because the climate state includes large, ready positive feedbacks provided by the Arctic sea ice, the West Antarctic ice sheet, and much of Greenland’s ice. Little additional forcing is needed to trigger these feedbacks and magnify global warming. If we go over the edge, we will transition to an environment far outside the range that has been experienced by humanity, and there will be no return within any foreseeable future generation.​

Scientific studies published in 2014 suggest that the loss of some Antarctic glaciers may already be unstoppable, even with a complete cessation of greenhouse gas emissions [Carrington], [Goldenberg].

DK
 

David J

Member
Thanks for clarification David. It is that "non-linear" nature of the crisis which gets so little main-stream attention. I am also seeing lots of people who think it is already too late and are "prepping". Hard to calculate what you would be "prepping" for, it seems to me. Or the city of Miami hoping to "mitigate" the effects of sea level rise- how much? By when?
 
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