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The Deep-Dive Series, part 4: Tipping Points
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The Deep-Dive Series, part 4: Tipping Points

What keeps you up at night? Finances? Work? Kids? Covid-19 concerns? For us here at Capture, we’ve been adding to our list… we’ve been learning more about something called ‘tipping points’. A tipping point in the climate system is a threshold that, when exceeded, can lead to large changes in the state of the system. It’s important to remember that these tipping points are not always abrupt, but may take thousands or millions of years to take place. However, that doesn’t mean that we shouldn’t still be immensely concerned about them. 


In this post, we explore what tipping points actually are (for example, did you know there are thought to be about 9 major tipping points for our climate?) and unpack why this all matters.


From declining Arctic sea ice to record-breaking heat waves to melting glaciers and worsening droughts, the disastrous effects of the global average temperature rises are being felt around the world. And as many as you know, it’s only going to get worse. But perhaps the most frightening aspect of climate change is that effects may not happen incrementally, (as a steadily rising line on a graph), but in a series of drastic lurches as various “tipping points” are passed. 


Tipping points are reached when certain impacts of global heating become unstoppable - for example, the runaway loss of ice sheets or forests. We are talking about thresholds where a tiny change could push a key component of the climate system into a completely new state. The additional concern is that we could encounter a chain reaction of multiple tipping points, creating irreversible problems for the world; opening the floodgates to a hotter, inhabitable planet. 


We spoke to our resident climate science advisor, Jake, to find out more about why we can’t simply reverse the effects of climate change: “If we heat the world by 2°C, and go back to 0°C warming again, that doesn't mean we return to the 0°C degree world we know. Some things once they’ve gone, don’t come back.” He gives the example about the poles, “One of the reasons that we can sustain frozen poles is because the reflective properties of the ice itself lowers the amount of heat being absorbed at the high latitudes. Once the ice is gone, even if you return to a pre-warming world it is thought highly unlikely that the ice will return."


The idea of tipping points was first introduced by the Intergovernmental Panel on Climate Change (IPCC) two decades ago. At the time, these large-scale disruptions in the climate system were considered probable only if global warming exceeded 5 °C above pre-industrial levels. However, the IPCC is singing a very different tune now, suggesting that tipping points could be exceeded even between 1 and 2 °C of warming. 


The tipping points discussed here come within one of three general categories:


  1. Runaway loss of ice sheets that accelerate sea level rise, 

  2. Forests and other carbon stores (e.g. permafrost) releasing carbon dioxide into the atmosphere, accelerating warming 

  3. The altering of planetary circulation systems


In recent years, research has begun to focus more on the potential for a cascade of tipping points. 


The ‘domino effect’ of activating tipping points. Source: Lenton et al, Nature, 2019



One of the largest current concerns is for the future of the global ocean circulation system, a key regulator of climate through the storage and transporting of heat, carbon, nutrients and freshwater all around the world. The melting Greenland ice combined with an Arctic experiencing rising temperatures has driven a key component of ocean circulation to a thousand-year low. If there is any further decline, changes could lead to a shift in heat distribution around the planet, which in turn could trigger forest collapse in the Amazon, drought in Africa’s Sahel region, disruption for Asia’s monsoon season, rapidly warm the Southern ocean, which which would in turn cause a surge in global sea levels as the West Antarctic Ice Sheet disintegrates… all culminating in potentially shifting the planet to a new climate regime that scientists term ‘Hothouse Earth’. Yep, this information is not for the faint-hearted.


Not all scientists would however support this argument that the earth is close to crossing major tipping points. Professor Mike Hulme, a climate scientist based at the University of Cambridge, completely dismissed new analysis shared in a 2019 Nature article “a speculative opinion from a small group of self-selecting scientists.” He went on to say that “there are no new research findings presented here” and that “many earth systems scientists would challenge the view” that the earth is close to crossing major tipping points. 


However, Professor Lenton and his team at Exeter University agree that there is a certain degree of speculation involved when it comes to tipping points, as there is with most climate science predictor models, but that “given its huge impact and irreversible nature...to err on the side of danger is not a responsible option.” Tipping points are simply too risky to bet against. He makes an important statement: The “climate emergency” is not just political rhetoric. It is an established, proven scientific fact. Whether or not governments and their administrations choose to take it seriously does not take away from the fact that every day, things are escalating. The recently published article in Nature was released around the same time as a new report stating that greenhouse gas emissions have hit a record high, with 38.6 billion tons of CO2 being pumped into the atmosphere in 2019.


We are becoming increasingly familiar with politicians citing opinions simply with a reference to ‘scientists say’ or ‘we are following the advice of scientists’. But what happens when scientists disagree? Jake said “there’s more uncertainty around certain tipping points than other (climate issues)... predicting changes in the dynamics of the atmosphere is more uncertain than the dynamics of land because the atmosphere is chaotic and hard to model.” When scientists talk about physical dynamics of ice sheets, they do so with less uncertainty than for shifting monsoons, or the change in ocean circulation.


In 2008, Lenton and his team determined 15 potential tipping points. Now, seven of them show signs of being “active”, along with two new tipping points added to the list. Four of these nine active tipping points involve thawing ice, with Arctic sea ice rapidly disappearing and ice loss accelerating on three of the planet’s large, land-based ice sheets: Greenland, West Antarctica, and the Wilkes Basin in East Antarctica. Lenton says that the latter two are “showing evidence consistent with having passed a tipping point”, meaning that more ice loss may not be preventable anymore. Greenland is only a step behind, with models suggesting that this ice sheet could be doomed at 1.5 °C of warming, which is predicted to happen as soon as 2030, according to the research. As a result of this, sea levels could rise by around 13 meters (43 feet). But this may take anywhere between centuries to millennia to take place... 


However, no matter the time frame, once this begins, it will be virtually unstoppable.


So, onto the other categories of tipping points… 4 already-active tipping points involve the biosphere and its stores of carbon. Forests, which today cover 30% of the world’s land surface are being rapidly and directly transformed in many areas by the impacts of expanding human populations and economies. The Amazon rainforest has been suffering from recurring droughts and forest dieback while rising temperatures are triggering numerous forest fires and pests in the boreal forests of the far North. Meanwhile, permafrost is thawing and releasing methane, a greenhouse gas; and in the tropics, coral reefs are suffering massive die-offs, threatening wider ocean ecosystems. 


While ice sheets may slowly deteriorate, passing biospheric tipping points will cause much more sudden, immediate, obvious changes. Deforestation in the Amazon is already having negative effects on its health, reducing rainfall and lengthening the dry season to a point where the trees cannot survive and/or are consumed by fires. Carlos Nobre of the University of São Paulo, says that “when the dry season becomes longer than four months, tropical forest turns to savanna.” The tipping point for the Amazon is placed at 40% tree loss, a figure that the already changing global climate could reduce to between 20% - 25% by 2050. 


As these tipping points will have more abrupt effects, it is feared that sudden release of carbon dioxide from these natural carbon stores could drastically reduce the leeway the world has for avoiding global warming above 1.5 degrees, the target set by the 2015 Paris Agreement. This would mean that we need to limit future CO2 emissions to about 500 billion tons, which is roughly 12 years of emissions at current rates. However, the abrupt forest dieback in Amazon and boreal forests, combined with methane emissions from thawing permafrost, could use up 300 billion tons of that emissions budget, meaning that there would be far more than 500 billion tons of carbon dioxide released. We are concerned that we will not be able to realistically stick to that number, especially based on how emissions increased in 2019.


Tipping points have been understood and developed for quite some time now. The only change is that more research has determined that there are more tipping points than we previously thought, and the predictions of the time it will take before they are activated has become much shorter. As we wrote earlier, the real new concern is the potential for a cascade of tipping points, in which breaching one will send everything tumbling down, leading to a rapid escalation of damage. Yikes.


The linchpin of a cascade like this, (or as we might put it more frankly, ‘the trigger of destruction’), is the ninth tipping point that has recently been identified as active; a critical feature of the global ocean circulation system, known as the Atlantic Meridional Overturning Circulation, or AMOC.


Okay, here’s where it may get a little more technical... The AMOC is a large system of ocean currents, like a conveyor belt, driven by differences in temperature and salt content – the water’s density. As warm water flows northwards it cools and some evaporation occurs, which increases the amount of salt. Low temperature and a high salt content make the water denser, and this dense water sinks deep into the ocean. The cold, dense water slowly spreads southwards, several kilometres below the surface. Eventually, it gets pulled back to the surface and warms in a process called “upwelling” and the circulation is complete. This process may be the prime regulator for global climate. It is the main reason why the Northern Hemisphere is warmer than the Southern hemisphere. But, like everything on Earth, it is being disrupted.


Stefan Rahmstorf, an oceanographer at the University of Potsdam and a co-author of the new analysis, said “Arctic warming and Greenland melting are driving an influx of fresh water into the North Atlantic.” The fresher water is less dense and sinks less. Rahmstorf calculates that, as a result, the AMOC has weakened by about 15% since global warming took hold in 1975. “It is now at its weakest in the past millennium, or even longer,” he continued. 


This disruption to the cycle and decline of ocean circulation threatens to trigger other tipping points. These are the effects of a slow down of the AMOC:

  • Reducing rainfall over the Amazon basin

  • Disrupting monsoon systems in Asia and West Africa, which could trigger drought in the Sahel

  • Transporting warm waters into the Southern Ocean, which could further destabilize ice in Antarctica, resulting in rising sea levels


Most climate models predict that the global ocean circulation will continue to be weakened throughout this century, but are unsure on how close we might be to a tipping point. The question is not whether these tipping points will be triggered, but when. 


Knowing this information, researchers wonder whether it is time for governments to collectively declare a climate emergency. Their Nature paper concludes, “In our view, the evidence from tipping points alone suggests that we are in a state of planetary emergency”. With time running out, it has become even more urgent that governments act towards reducing their emissions and mitigating the consequences of climate change. 


So what are the proposed solutions? Some pretty radical technologies have been proposed that are collectively known as geo-engineering.


There are geo-engineering projects in development such as deploying devices to shade us from solar radiation. Governments could rush to develop technology that may ultimately mess with the laws of nature, instead of making moves to reduce emissions or implementing low-carbon energy. Jake describes geo-engineering “as one of the most contentious areas of climate science, as you are deliberately trying to interfere with the dynamics of the planet to alter the climate.”


And it can sounds like something from a science-fiction movie… ideas have included:

  • Injecting particles into the atmosphere that radiate heat

  • Injecting salt into the high altitudes to increase the strength of ocean circulation

  • Artificially creating ice at high altitudes to increase reflection 


Plenty of scientists oppose geo-engineering, Proff Lenton calls them ‘as risky as the risks we are trying to avoid.’ He is not alone in this opinion; Jake stresses upon the fact that “most people see geo-engineering as far-fetched and impossibly difficult to get right. The main focus is, and should be, mitigation and adaptation.” 


As you can see; not only do we have to worry about warming temperatures, we have to worry that at some point the warming of the earth will no longer be something we can control or work towards preventing. We must work faster and harder together (governments, businesses, individuals) to reduce our emissions and attempt to pause climate change effects that are already taking place. While COVID-19 has resulted in lower air emissions and air pollution, this will not be enough to prevent tipping points from breaching.


So… you’ve learned more about tipping points - what can you do? There are so many ways that you can support the transition to a greener planet, but here are a few ideas to get you started: write to your local politician, buy from brands that share your values, support organisations such as Greenpeace, share this article on social media, make sure your finances aren’t supporting fossil fuels, and if you are interested in how you can reduce and offset emissions from your everyday life, download Capture here for our iPhone users and here for our android users.



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