Last week a new paper in Nature caused a stir and world-wide headlines, and for good reason.
“Climate tipping points – too risky to bet against” by Lenton, Rockstrom, Gaffney, Rahmstrof, Richardson, Steffen and Schellnhuber look at the “evidence on the threat of exceeding (climate system) tipping points, and whether we still have any control over them” because this “helps to define that we are in a climate emergency.”
Now this will be familiar territory to regular readers of this blog. Philip Sutton and I used this language almost 12 years ago in the book “Climate Code Red”, and we have witnessed a recent mass engagement in this idea, including climate emergency declarations by more than 1200 councils around the world, the Oxford Dictionary naming “climate emergency” its word of the year, the resolution last week by the European Parliament, and much more.
In particular, tipping points are “more likely than was thought, have high impacts and are interconnected across different biophysical systems, potentially committing the world to long-term irreversible changes”. These include:
- “Several cryosphere tipping points are dangerously close”… “West Antarctica might have passed a tipping point”.. “part of the East Antarctic ice sheet — the Wilkes Basin — might be similarly unstable.”
- “Models suggest that the Greenland ice sheet could be doomed at 1.5 °C of warming, which could happen as soon as 2030”.
- “We might already have committed future generations to living with sea-level rises of around 10 metres over thousands of years. But that time scale is still under our control. The rate of melting depends on the magnitude of warming above the tipping point.”
- “Other tipping points could be triggered at low levels of global warming… a cluster of abrupt shifts between 1.5 °C and 2 °C, several of which involve (Arctic) sea ice.”
- “Biosphere tipping points can trigger abrupt carbon release back to the atmosphere.. Permafrost across the Arctic is beginning to irreversibly thaw and release carbon dioxide and methane… the boreal forest in the subarctic is increasingly vulnerable.”
- “Estimates of where an Amazon tipping point could lie range from 40% deforestation to just 20% forest-cover loss8. About 17% has been lost since 1970.”
The authors say that “the clearest emergency would be if we were approaching a global cascade of tipping points that led to a new, less habitable, ‘hothouse’ climate state. Interactions could happen through ocean and atmospheric circulation or through feedbacks that increase greenhouse-gas levels and global temperature. Alternatively, strong cloud feedbacks could cause a global tipping point. We argue that cascading effects might be common. Research last year analysed 30 types of regime shift spanning physical climate and ecological systems… This indicated that exceeding tipping points in one system can increase the risk of crossing them in others. Such links were found for 45% of possible interactions. In our view, examples are starting to be observed.”
This is a question of risks, and acting in a way that reduces the chances of a very bad outcome to the minimum. And then there is also the compelling evidence from past climates:
“The Earth system has been unstable across multiple timescales before, under relatively weak forcing caused by changes in Earth’s orbit. Now we are strongly forcing the system, with atmospheric CO2 concentration and global temperature increasing at rates that are an order of magnitude higher than those during the most recent deglaciation… Atmospheric CO2 is already at levels last seen around four million years ago, in the Pliocene epoch. It is rapidly heading towards levels last seen some 50 million years ago — in the Eocene — when temperatures were up to 14 °C higher than they were in pre-industrial times.”
The conclusion to be drawn from all of this is that the threat, the risks, are overwhelming. And in a slap to conventional economic modelling of climate risks, they write that: “If damaging tipping cascades can occur and a global tipping point cannot be ruled out, then this is an existential threat to civilization. No amount of economic cost–benefit analysis is going to help us. We need to change our approach to the climate problem.”
Existential, acute crisis… the words may vary, but the message is unambiguous: “The evidence from tipping points alone suggests that we are in a state of planetary emergency: both the risk and urgency of the situation are acute.”
Climate emergency formula
The paper then provides a formula to helping understand the emergency:
E = R × U = p × D × τ / T
“We define emergency (E) as the product of risk and urgency. Risk (R) is defined by insurers as probability (p) multiplied by damage (D). Urgency (U) is defined in emergency situations as reaction time to an alert (τ) divided by the intervention time left to avoid a bad outcome (T). The situation is an emergency if both risk and urgency are high. If reaction time is longer than the intervention time left (τ / T > 1), we have lost control.”
To understand reaction versus intervention time, the Titanic example may help:
- Reaction time to an alert (τ) is the time it would take to correct the situation, i.e. turn Titanic around.
- Intervention time (T) is time left to actually act. i.e. time left to change course.
- In this case τ was much greater than T, and “losing control” (ship hits iceberg) was inevitable.
So a big question with climate is whether τ > T.
What is reaction climate τ ? It is conventionally said to be 30 years to get to zero (2050). How much could this be reduced?
What is the value of climate T?. Do we have any intervention time left, or not? The authors answer this question as follows:
“We argue that the intervention time left to prevent tipping could already have shrunk towards zero, whereas the reaction time to achieve net zero emissions is 30 years at best. Hence we might already have lost control of whether tipping happens. A saving grace is that the rate at which damage accumulates from tipping — and hence the risk posed — could still be under our control to some extent.”
Conclusion: A choice of disruptions
Reaction time to get to zero emissions is generally considered to be 30 years because a shorter time may not be viable due to (a) physical constraints or (b) the process would be too economically disruptive. The paper says “it is 30 years at best”, but this is not hard and fast: in an emergency or a top-priority process (e.g. Manhattan project, the moon shot, and so on) it is possible to compress timelines.
The big question is this: what happens if the actually available intervention time were 10-15 years? That is, if emissions are not zero in 10-15 years, the risk of “losing control” ramps up? Then, in order not to lose control, all efforts would need to be made to reduce the reaction time to less than 10-15 years, even though this may be very socially and economically disruptive.
To put it bluntly, the choice may be existential disruption because we lose control of the system (τ > T) OR large-scale socio-economic disruption, but much preferable to the existential outcome, by creating a shorter τ , such that τ < T.
How close is losing control and how short is the intervention time? There is no precise numerical answer, but the evidence suggests there is an unacceptable risk that it is very low. As the authors say, “we might already have lost control of whether tipping happens”.
If the intervention time has already “shrunk towards zero” as the paper suggests, then consideration of and research into short-term cooling measures such as solar radiation management must be a high priority to determine whether such measures are of net social and environmental benefit to provide some temporary cooling whilst other measures take effect.
Time is not on our side.