What you need to know about...Tipping points

By Luke Hatton 

Imagine for a second you’re leaning back in your chair whilst reading this. As any bored school-child has probably tested out, as you continue to lean back you’ll reach a point where you can feel yourself almost about to fall. A small push later and you’ll end up flat on your back.

This point is called the tipping point (surprise surprise!), and is often bandied around in relation to climate change and international climate negotiations. To understand its importance we have to dig a bit deeper into the global climate system and its complexities. 

When we talk about the climate system, we are talking about the collection of processes that control the climate (the average weather over a period of several decades), such as ocean currents and wind patterns. It can change as a result of 

1. internal variability (natural fluctuations without any clear cause)
   
2. external forces - e.g. 
   
   1. stronger energy output from the sun
      
   2. volcanic eruptions that block out sunlight, 
      
   3. (most significantly) human activity that releases emissions.
      

The climate system is incredibly complex, with thousands of different processes affecting different areas of the planet and interacting to influence the global climate. Each of the elements of the climate system react to external forcing differently; whilst some parts may respond to a change in the intensity of the sunlight entering the Earth's atmosphere, others may take centuries to reach a new balance.

Feedback loops
The complexity is increased further by the effect of feedback. A feedback loop is where the outcome of a process goes on to amplify or reduce the effect of an initial change to the system. This can work in one of two ways:positive (where the output amplifies the initial change) negative (where the system reduces the initial change).

In the case of climate change, negative feedback would be a welcome respite from the struggle we are having to decarbonise - while positive feedback loops could spell a grave threat to the Earth and our way of life.

Positive Feedback loop: melting ice sheets 

The most easily understood positive feedback in the climate is linked to the Antarctic and Arctic ice sheets outlined in the process below

1. Global warming cause ice sheets to melt
   
2. The total amount of sunlight that is reflected off the Earth’s surface is reduced (ice reflects far more sunlight than water, which tends instead to absorb it and its heat.) 
   
3. Consequently, the planet absorbs more heat from the sun’s rays
   
4. By causing more heat to be absorbed, the melting ice sheets will therefore amplify the effect of global warming that caused them to melt in the first place
   

 Other examples of positive feedback loops include:

• The thawing of permafrost in the Arctic circle (https://www.oxfordclimatesociety.com/blog/not-so-perma-frost-climate-change-and-its-impact-on-permafrost)
  
• Increasing severity and risk of forest fires globally (https://www.oxfordclimatesociety.com/blog/december-31st-2019 ) 
  
• Rising ocean temperatures, which reduces the ability of the oceans to act as a carbon store.
  

Feedback in the climate also comes in the form of negative feedback. The increase in global temperatures could lead to a rise in cloud coverage. The increased cloud thickness could reduce and reflect incoming sunlight, limiting global warming - in much the same way as melting ice coverage could increase global warming. 

Unfortunately for us, scientific studies have shown that there is a net positive feedback to global warming - meaning we can’t count on the planet to get us out of this mess. 

The tipping points in climate change refers to the global temperature rises that will kick these positive feedback mechanisms into action. The most up to date research on this is worrying to say the least. ‘Hothouse Earth’, a study published in the Proceedings of the National Academy of Sciences in 2019, examined ten natural feedback processes and concluded that even if the emissions targets set in the Paris Agreement are met, there is a risk of the Earth seeing a long term rise of 4 to 5 degrees on pre-industrial levels as a result of tipping points being crossed. 

Tipping points are also largely estimates rather than concrete thresholds, with even the IPCC being unsure of the precise levels of climate change which will trigger tipping points. This uncertainty adds a new dimension to the risks of climate change - and could mean that we have already crossed a tipping point. Johan Rockstrom, co-author of ‘Hothouse Earth’ warns that tipping points are likely to be linked, and that crossing one could set off others in a potentially catastrophic chain of dominoes.

If the case for immediate climate action was not strong enough already, the findings of research into these tipping points should be enough to justify radical change as we push towards a zero-emissions emissions society. Going back to the chair, if you were tempted to lean back again and shift your weight forward at the tipping point, you’d right yourself. No such trick exists for the global climate - and we’ll be left with far more than just bruises to deal with if we do exceed the tipping point(s). 


References

https://www.theguardian.com/environment/2019/nov/27/climate-emergency-world-may-have-crossed-tipping-points

https://www.nature.com/articles/d41586-019-03595-0

https://www.stockholmresilience.org/research/research-news/2018-08-06-planet-at-risk-of-heading-towards-hothouse-earth-state.html

https://climate.nasa.gov/nasa_science/science/

https://www.theguardian.com/environment/2018/oct/09/tipping-points-could-exacerbate-climate-crisis-scientists-fear