Climate Tipping Points – An Existential Threat to Civilisation

Cliff Mitchell - 05/01/2020

Connected tipping points

Are we about to trigger a collapse of Earth's life support systems?


We know that climate change is happening, is man-made, and is very, very serious. But it could get a lot worse, and very quickly, due to climate tipping points. According to scientists writing in the hugely respected Nature, that possibility is “an existential threat to civilisation”.

So what are climate tipping points and why are they so dangerous?

A tipping point in the climate system is a threshold that, when exceeded, can lead to large changes in the state of the entire system - they are irreversible changes in the climate system. The earth’s climate has been largely in a state of equilibrium for thousands of years but we are throwing our climate system out of balance by pumping vast quantities of greenhouse gases into our atmosphere. This is leading to global warming and all of the associated consequences, and it is happening faster than expected. However, if we hit a series of tipping points the changes could be rapid and massive.

Such a collapse of Earth’s systems could lead to “hothouse earth” conditions with a global temperature rise of 5 degrees C, sea levels rising 20 to 30 feet, the complete loss of the world’s coral reefs and the Amazon forest, and with large parts of the planet uninhabitable.

A global emergency response is required to limit warming to 1.5 degrees Celsius , the authors warn.

“The stability and resilience of our planet is in peril,” they say.
“It’s a nasty shock that tipping points we thought might happen well into the future are already underway,” says Tim Lenton, lead author of the Nature article.

For example, the slow collapse of the West Antarctic ice sheet appears to be in progress. The latest data show that the same thing might be happening to part of the East Antarctic ice sheet, says Lenton, a climate scientist at University of Exeter. If those both melted, they could raise sea levels 21 feet (7 metres) over the next few hundred years.

Cascading tipping points – pass one, get many

As if this wasn’t bad enough scientitsts tell us that crossing a threshold in one part of the climate system may trigger another tipping element to tip into a new state. These are so-called cascading tipping points.

For example, ice loss in West Antarctica and Greenland will significantly alter ocean circulation. Sustained warming of the northern high latitudes as a result of this process could activate tipping elements in that region, such as permafrost degradation, loss of Arctic sea ice, and Boreal forest dieback.

So tipping points may not happen in isolation. The impact of passing one tipping point may in itself trigger the crossing of other tipping points in a cascade effect. An overview of some of the ‘connectivity’ of tipping points is shown in this figure from Nature.

What are the main tipping points?

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 collapse even before a global temperature rise of two degrees Celsius.

While these are the most urgent and worrying tupping points, there are many more that may be further off, or less certain, but could be just as disastrous.

Tipping points potentially further out

  • 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 stability of 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 RainforestDeforestation, 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 hole within 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.

Are we doomed?

None of this is inevitable. A global emergency response is required to limit warming to 1.5 degrees Celsius if we are to maintain the stability and resilience of our planet.
Solutions exist but time is running out.

Fortunately there are also social tipping points including an economic tipping point where the price of renewable energy is dropping below fossil fuels in market after market.

“The prices for renewables keep falling and performance is improving. This is an unbeatable combination.” says Owen Gaffney, one of the authors of the Nature paper.

More and more countries such as the United Kingdom have reached a political tipping point and adopted 2050 net zero carbon targets. “There is now confidence it is achievable and affordable,” he said.

And in the United States, candidates for the 2020 presidential elections are putting out ambitious climate action plans.

Over the last 12 months a broad societal awareness tipping point appears to have been reached—the Greta Thunberg effect—with millions of young student strikers and many others demanding urgent climate action. At the same time, more and more finance companies, businesses, and cities are adopting tough climate targets.

“These tipping points are converging that could make the 2020s the fastest economic transition in history,” Gaffney says.

This existential threat to civilisation can be averted, we know what needs to be done, the technology required exists, but the political will to drive the necessary profound changes is still inadequate. What we need is more social and economic tipping points, and that’s where we as individuals can make a real difference.

It is too late to be a bystander – you MUST be a participant.

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