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Positive Feedback and Tipping Points

A couple of geeky explanations for why things might get worse than you think. All the more reason to act.

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• 6 min read
Clip-art type simple drawing of a silouetted figure leaning back too far in a chair so it is about to fall over.
Past the tipping point.
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Tipping Points
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We at SweetLightning don’t dwell much on the gloom and doom that can accompany discourse on most aspects of climate change. However, occasionally it’s helpful to face up squarely to some underlying warming mechanisms to better understand how they work, and perhaps to underscore the urgency to act. In this article we’ll look at two such mechanisms that are commonly misunderstood.

Positive Feedback

We don’t mean the “well done” comment we might get from the boss at the end of a project, or rather don’t mean only that. In the scientific and engineering world, positive feedback has a specific definition, as does negative feedback. Both adjectives describe actions in cause-and-effect loops, but don’t have anything to do with desirability of the outcome.

Negative feedback loops dampen down the reaction of a process. A familiar example is a thermostat controlling a heating system in your dwelling. The temperature in the space drops, the thermostat turns on the heat, the room warms up, and the thermostat turns the heat off. Room temperature equilibrium is reached, a desirable outcome.

Positive feedback loops amplify the reaction of whatever process is being described or controlled. They are, in effect, self-reinforcing. The most common everyday example these days is the viral social media post. Other social examples include Ponzi schemes, runs on banks, and stock market crashes. These are all positive feedback loops with undesirable outcomes.

Mechanisms that determine climate include both negative and positive feedback loops, which have been in balance in the pre-industrial past.  Climate change is being driven in part by a number of positive feedback loops that outweigh the negative loops. We’ll look at just two.1

The first is atmospheric water vapour feedback. Water vapour is the most potent GHG, as we pointed out in a previous article. More water vapour in the air traps more heat, warmer air holds more water vapour, trapping more heat and so on – not good.

Second is ice albedo feedback. Ice is more reflective (higher albedo) than water or land, reflecting solar energy back into space. A warming climate melts more glacial and polar ice, lowering the overall planetary albedo, reflecting less heat into space, warming the planet, melting more ice, lowering albedo . . .

Tipping Points

Many of us first became aware of tipping points by reading Malcolm Gladwell’s 2000 book, “The Tipping Point”. He focused on the phenomenon in social systems by showing how some small initial change can cause a system to pass some threshold or reach critical mass. Fashion trends, started by a few influencers, are typical social tipping points.

The tipping point concept in physical sciences is a little different, and has a much longer history that evolved from mathematical ideas related to feedback loops. Today, tipping points in climate systems “occur when change in large parts of the climate system — known as tipping elements — become self-perpetuating beyond a warming threshold.”2 Essentially, positive feedback loops outweigh stabilizing negative loops to drive irreversible changes.3 It’s akin to rocking your chair back on two legs. You can tip it so far with nothing drastic happening, but push it just a tiny bit more and you can’t stop yourself from falling over.

Potential climate change tipping points abound: melting polar ice sheets, collapse of the Gulf Stream, thawing permafrost, Amazon and boreal forest dieback, monsoon failure, ocean acidification, and others. Let’s look at a couple that have the lowest thresholds and potentially the most severe consequences.

 Ice sheet melting

A lot of water is locked up in polar ice sitting on land. If some or all of that ice melts into the ocean, global sea levels will rise significantly. The Greenland Ice Sheet and West Antarctic Ice Sheet are particularly at risk.

High-confidence predictions suggest about a third of a metre sea-level rise from ice melt by 2100 under low emission scenarios. Lower-confidence predictions suggest up to fifteen metre rise is possible by 2300 under high-emission scenarios. With an estimated 230 million people living within one metre of sea level, and roughly 1 billion within 10 metres, it's not clear how well our civilization would cope with sea-level rise somewhere between the two extremes.4

Here’s the thing: that sea-level rise does not increase linearly as the world warms. Current (low-ish) rates of ice-melt-driven sea-level rise could rapidly increase with only small changes in global mean temperature, which is, in effect, a tipping point. Further, that melting is basically irreversible on human timescales, even if the global mean temperature were to be lowered.5

What is that global mean temperature tipping point? It could be as low as 1.7 to 2.3 degrees Celsius above pre-industrial levels.6 You likely don’t need reminding that we may already have missed the Paris Agreement target of limiting warming to 1.5 Celsius.

 AMOC weakening or collapse

Most of us will have heard of the Gulf Stream, which runs up the east coast of North America, carrying warm tropical Atlantic water north. It is just one segment of a larger system of global ocean currents that connect the Atlantic Ocean to the Indo-Pacific and Southern Oceans. The Atlantic Ocean part is known as the Atlantic Meridional Overturning Circulation (AMOC). AMOC is a kind of conveyor belt of surface and sub-surface ocean currents that transport tropical heat to the north Atlantic, where the water cools and forms ice. Salt is excluded from sea ice when it forms, which increases the seawater’s salt concentration and therefore its density. The cooled, saltier, denser water sinks and moves south again, in a cycle that takes about 1,000 years to complete.7

The AMOC keeps northern Europe much warmer than its latitude would suggest. AMOC also plays a role in regulating climate change by transporting excess atmospheric CO2 into the deep ocean. If AMOC weakens substantially, or fails completely, the climate in northern Europe would cool drastically, significantly affecting everything from heating systems to agriculture.

What would cause AMOC to weaken? If sufficient ice melts from the Greenland Ice Sheet, the resulting fresh water could decrease the density of the seawater there, enough to prevent the water from sinking, interrupting the mechanism that drives the circulation.

Predicting the future behaviour of AMOC involves modelling the entire complex system of global currents, with a great deal of assumptions and much uncertainty. At least one study suggests that measured weakening to date, together with the current trajectory of future GHG emissions, could lead to AMOC collapse by the middle of this century.8

Another study considered the other end of the conveyor belt of currents, the Indo-Pacific. It found that while AMOC is very likely to weaken significantly with increased global temperatures, due to off-setting changes in the Pacific Ocean currents, it will not likely collapse altogether.9

Whether AMOC collapses or just weakens, the effects on climates around the North Atlantic are likely to be severe, adaptation will be difficult, and (given the 1,000 year turnover) effectively irreversible on timescales we can intuitively grasp.

Understanding the consequences of feedback loops and tipping points built in to the climate system might seem depressing, but the understanding should strengthen our resolve to act to reduce GHG emissions.

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Reading

  1. Mauritsen, T., Graversen, R., Klocke, D., Langen, P., Stevens, B., & Tomassini, L. (2013). Climate feedback efficiency and synergy. Climate Dynamics, 41, 2539-2554. https://doi.org/10.1007/s00382-013-1808-7
  2. Armstrong McKay et al., “Exceeding 1.5°C Global Warming Could Trigger Multiple Climate Tipping Points.” 2022, Science, 377  https://www.science.org/doi/10.1126/science.abn7950
  3. Abrams et al., “Integrating Tipping Point Concepts across Diverse Systems.” https://www.nature.com/articles/s44458-026-00063-5
  4. Stokes, C.R., Bamber, J.L., Dutton, A. et al. Warming of +1.5 °C is too high for polar ice sheets. Commun Earth Environ 6, 351 (2025). https://doi.org/10.1038/s43247-025-02299-w
  5. Stokes et al., Ibid.
  6. Nils Bochow et al., “Overshooting the Critical Threshold for the Greenland Ice Sheet,” Nature 622, no. 7983 (2023): 528–36, https://doi.org/10.1038/s41586-023-06503-9.
  7. “The Atlantic Meridional Overturning Circulation (AMOC) | National Oceanography Centre,” March 23, 2026, https://www.noc.ac.uk/discover-the-ocean/oceans-explained/the-atlantic-meridional-overturning-circulation.
  8. Peter Ditlevsen and Susanne Ditlevsen, “Warning of a Forthcoming Collapse of the Atlantic Meridional Overturning Circulation,” Nature Communications 14, no. 1 (2023): 4254, https://doi.org/10.1038/s41467-023-39810-w.
  9. J. A. Baker et al., “Continued Atlantic Overturning Circulation Even under Climate Extremes,” Nature 638, no. 8052 (2025): 987–94, https://doi.org/10.1038/s41586-024-08544-0.