24 February 2023

Faster, higher, hotter: What we learned about the climate system in 2022 (3)

Third in a 3-part series  |  Part 1  |  Part 2

by David Spratt

So far this series has looked at:

  1. Emissions trends
  2. The 1.5°C target
  3. Overshooting and cooling back to 1.5°C
  4. The likelihood of achieving the 2°C target
  5. 2°C degrees is not a point of system stability
  6. We are heading towards 3°C or more
  7. System-level change and tipping points are happening faster than forecast

This post looks at cascading risks, climate extremes and necessary actions.

8    Risks are cascading, and underestimated 

Climate system feedbacks can drive abrupt, non-linear change that is difficult to model and forecast, with the Earth moving to dramatically different conditions. Such changes may be irreversible on relevant time frames, such as the span of a few human generations. Major tipping points are interrelated and may cascade, so that interactions between them lower the critical temperature thresholds at which each tipping point is passed.

Climate models do not yet incorporate key processes, and therefore are deficient, especially when projecting abrupt change, system cascades, and changes in the cryosphere and in the carbon cycle. Whether it be permafrost, Greenland or West Antarctica (and hence sea-level rises), the story is the same. Current climate models are not capturing all the risks, such as the stalling of the Gulf Stream, polar ice melt and the uptick in extreme weather events. Thus Earth system and Integrated Assessment Model projections, and their use in determining carbon budgets, are not reliable. It is important that observations, semi-empirical models, expert elicitations, and lessons from past climates are given more weight, given current model deficiencies.

In addition, the range of extremes being experienced today are greater than forecast in many instances. Prof. Andy Pitman, Director of the ARC Centre of Excellence for Climate Extremes  notes that global mean warming is badly understood.  He says as a general rule of thumb, global average warming of 4°C (covering land and ocean)  is consistent with 6°C over land, and 8°C in the average warming over mid-latitude land. That risks 10°C in the summer average, or perhaps 12°C in heatwaves. Western Sydney has already reached 48°C. If you add 12°C to the 48°C you get summer heatwaves of 60°C. 

It is well established that a tipping point may be abrupt and irreversible on relevant time frames, possibly leading to cascading events, even driving the system towards a “Hothouse Earth”.  In 2022, Will Steffen explained that: 

“The current trajectory is accelerating the [Earth] system towards [a point of] bifurcation, with the increasing risk that our pressures will push the system onto the ‘Hothouse Earth’ trajectory. The critical point here is that there is a point beyond which we lose control of the system and its own internal feedbacks drive it past a global threshold and irreversibly into a much hotter state… “ 

In 2022, Nico Wunderling et al. published “Global warming overshoots increase risks of climate tipping cascades in a network model”, which found that overshooting climate targets could significantly increase risk for tipping cascades. Wunderling explained:  “Even if we would manage to limit global warming to 1.5°C after an overshoot of more than 2°C, this would not be enough as the risk of triggering one or more global tipping points would still be more than 50% percent. With more warming in the long-term, the risks increase dramatically.” Jonathan Donges added: “To effectively prevent all tipping risks, the global mean temperature increase would need to be limited to no more than one degree – we are currently already at about 1.2°C.” 

Many cascades are well established, for example, that Arctic sea-ice loss driving enhanced Greenland deglaciation, which contributes to a slow of the AMOC, which in turn is decreasing rainfall over parts of the Amazon, and enhancing carbon losses. Now new research establishes a link between climate changes in the Amazon and the Tibetan Plateau. The researchers explain: “Our research confirms that Earth system tipping elements are indeed inter-linked even over long distances, and the Amazon is one key example how this could play out… When it’s getting warmer in the Amazon, it also does so in Tibet, hence for temperature there’s a positive correlation.”

The importance of a paper published last year by ten authors, including Steffen, cannot be underestimated in bringing together a high-level analysis on climate risks and the need for climate research to focus on the worse-case, high-end possibilities. The paper is “Climate Endgame: Exploring catastrophic climate change scenarios”  and its key findings include:

  • “Prudent risk management requires consideration of the bad-to-worst-case scenarios” because low-probability, high-impact extreme outcomes have damages are so large, as to perhaps be unquantifiable. Large uncertainties about dangerous surprises “are reasons to prioritize rather than neglect them”.
  • “Climate damages are likely to be nonlinear” and result in an even larger risk tail, with feedbacks in the carbon cycle and potential tipping points that could generate high greenhouse concentrations that are often missing from models.  There are even more uncertain feedbacks, which, in a very worst case, might amplify to an irreversible transition into a “Hothouse Earth” state including “recent simulations suggest that stratocumulus cloud decks might abruptly be lost at CO₂ concentrations that could be approached by the end of the century, causing an additional ∼8 °C global warming. Large uncertainties about dangerous surprises are reasons to prioritize rather than neglect them.”
  • Declining emissions does not rule out extreme climate change due to feedbacks in the carbon cycle and potential tipping points that could generate high greenhouse concentrations that are often missing from models. Examples include Arctic permafrost thawing that releases methane and CO2, carbon loss due to intense droughts and fires in the Amazon, and the apparent slowing of dampening feedbacks such as natural carbon sink capacity. These are likely to not be proportional to warming; instead, abrupt and/or irreversible changes may be triggered at a temperature threshold. Particularly worrying is a “tipping cascade” in which multiple tipping elements interact in such a way that tipping one threshold increases the likelihood of tipping another.

9    New climate extremes recorded in 2022 

2022 was  a big year for breaking-record, extreme climate events, including:

  • Large parts of the northern hemisphere were exceptionally hot and dry. Record breaking heatwaves were observed in China, Europe, North and South America.
  • Europe experienced its hottest summer ever recorded, with prolonged and intense heatwaves affecting western and northern Europe, and persistent low levels of rainfall leading to widespread drought conditions, and wildfires especially in Spain and Portugal.
  • The United Kingdom saw off-the-charts temperatures shattered records kept nearly as far back as William Shakespeare’s time, with a new national record on 19 July when the temperature topped more than 40°C  for the first time.
  • In East Africa, rainfall has been below average in four consecutive wet seasons, the longest in 40 years.
  • A large area around northern Argentina, southern Bolivia, central Chile, and most of Paraguay and Uruguay experienced record-breaking temperatures during two consecutive heatwaves in November–December 2022.
  • Prolonged heatwave conditions affected Pakistan and northern India in spring. In May, temperature exceeded 50°C (122°F) in Jacobabad, Pakistan, and more than a billion people in South Asia endured several months of almost uninterrupted temperatures above 100°F.
  • China had the most extensive and long-lasting heatwave since national records began and the second-driest summer on record. Heat waves and drought stretched over eight weeks and dried up parts of the Yangtze River to the lowest level since at least 1865.
  • In July and August, Pakistan saw record-breaking rainfall leading to large-scale flooding over one-third of the country causing widespread destruction and loss of life, with at least 1700 deaths and 33 million people affected. 7.9 million people displaced.
  • At Vostok station, in the interior of East Antarctica, the reported temperature reached -17.7°C, the warmest ever measured in its 65-year record.
  • 2022 took an exceptionally heavy toll on glaciers in the European Alps, with initial indications of record-shattering melt. 
  • The Greenland ice sheet lost mass for the 26th consecutive year and it rained (rather than snowed) on the summit for the first time in September.
Sources for extremes are here and here.

10    Conclusion

In summary, emissions still have not peaked and are unlikely to be significantly lower in 2030 than 2020; warming of 1.5°C is likely this decade; the emissions trend and reduction commitments are currently nowhere near keeping warming to 2°C; and once the full range of feedbacks, non-linearities and cascades are taking into account, warming may well exceed 3°C this century, a level of warming that will likely result in climate-driven collapse of ecological and social systems. The contradiction is stark: the world will sail past 1.5°C, but 1.5°C may be enough to trigger ‘Hothouse Earth’ cascades; indeed, it is evident that some tipping points have already been passed, and some cascading events are occurring already.

So what to do? Last year, in the concluding section of Climate Dominoes, I wrote the following. It seems just as apt today:

Decarbonisation is not enough. Even sharp reductions in emissions will not be enough to avoid crossing the 1.5°C threshold, and very likely the 2°C threshold, given record-breaking use of fossil fuels. It is a big mistake to think we can “park” the Earth System at any given temperature rise – say 2°C  – and expect it to stay there. 2°C may not be a point of system stability. Reducing the level of atmospheric CO₂ by carbon drawdown is vital, but the drawdown impact is relatively slow. The more damaging impacts, and risk of triggering non-linear events — associated with a higher level of warming for several decades in overshoot scenarios — are understated or ignored. The need to cool the planet in order to avoid cascade/collapse/”Hothouse” scenarios needs to be taken seriously. There are proposals for more direct cooling of threatened systems — as advocated, for example, by the Climate Crisis Advisory Group and the Cambridge Centre for Climate Repair for the Arctic with marine cloud brightening — or of the planet as a whole, whether by mirrors or sulfates. Whilst not yet proven to be of net benefit, and/or cost effective, such proposals seem vital if Earth is to be kept below a level of warming where more system tipping points are activated and cascade into an avalanche of warming and system feedbacks that human actions will no longer have the capacity to rein in.