According to the scientists behind "planetary boundaries", we are perilously close to climate tipping points
We like to be a can-do site - but sometimes we have to bring you information that is more like “can’t afford not to”.
From the esteemed science journal Nature, the authors behind the concept of planetary environmental boundaries (which informs Kate Raworth’s Doughnut Economics) are urgently telling us this week (PDF copy) that we are threatening “tipping points” in the climate crisis:
Politicians, economists and even some natural scientists have tended to assume that tipping points1 in the Earth system — such as the loss of the Amazon rainforest or the West Antarctic ice sheet — are of low probability and little understood.
Yet evidence is mounting that these events could be more likely than was thought, have high impacts and are interconnected across different biophysical systems, potentially committing the world to long-term irreversible changes.
Here we summarize evidence on the threat of exceeding tipping points, identify knowledge gaps and suggest how these should be plugged. We explore the effects of such large-scale changes, how quickly they might unfold and whether we still have any control over them.
In our view, the consideration of tipping points helps to define that we are in a climate emergency and strengthens this year’s chorus of calls for urgent climate action — from schoolchildren to scientists, cities and countries.
The Intergovernmental Panel on Climate Change (IPCC) introduced the idea of tipping points two decades ago. At that time, these ‘large-scale discontinuities’ in the climate system were considered likely only if global warming exceeded 5 °C above pre-industrial levels.
Information summarized in the two most recent IPCC Special Reports (published in 2018 and in September this year)2,3 suggests that tipping points could be exceeded even between 1 and 2 °C of warming (see ‘Too close for comfort’).
If current national pledges to reduce greenhouse-gas emissions are implemented — and that’s a big ‘if’ — they are likely to result in at least 3 °C of global warming. This is despite the goal of the 2015 Paris agreement to limit warming to well below 2 °C. Some economists, assuming that climate tipping points are of very low probability (even if they would be catastrophic), have suggested that 3 °C warming is optimal from a cost–benefit perspective.
However, if tipping points are looking more likely, then the ‘optimal policy’ recommendation of simple cost–benefit climate-economy models4 aligns with those of the recent IPCC report2.
In other words, warming must be limited to 1.5 °C. This requires an emergency response.
Please read the paper in depth (PDF copy) - it repays close study.
Their evidence comes from:-
Study of possible ice collapse. We could “destabilize the rest of the West Antarctic ice sheet like toppling dominoes — leading to about 3 metres of sea-level rise on a timescale of centuries to millennia”
Biosphere boundaries being breached, and this causing cascades of change through connected ecosystems (see graphic). They make this chilling point:
“The world’s remaining emissions budget for a 50:50 chance of staying within 1.5 °C of warming is only about 500 gigatonnes (Gt) of CO2. Permafrost emissions could take an estimated 20% (100 Gt CO2) off this budget10, and that’s without including methane from deep permafrost or undersea hydrates.
“If forests are close to tipping points, Amazon dieback could release another 90 Gt CO2 and boreal forests a further 110 Gt CO211. With global total CO2 emissions still at more than 40 Gt per year, the remaining budget could be all but erased already.
The authors conclude:
Some scientists counter that the possibility of global tipping remains highly speculative. It is our position that, given its huge impact and irreversible nature, any serious risk assessment must consider the evidence, however limited our understanding might still be. To err on the side of danger is not a responsible option.
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.
In our view, 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.
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.
The stability and resilience of our planet is in peril. International action — not just words — must reflect this.