Tipping points in climate emergency

New Research in June 2020 demonstrates the ongoing sixth mass extinction may be the most serious environmental threat to the persistence of civilization, because it is irreversible. Tipping points are happening.

Leading Stanford University biologists and researchers examined data on 29,400 land vertebrate species compiled by the IUCN Red List of Threatened Species and Birdlife International. The researchers identified 515 species with populations below 1,000 and about half of these had fewer than 250 remaining. Most of these mammals, birds, reptiles and amphibians were found in tropical and subtropical regions.

Scientists discovered that 388 species of land vertebrate had populations under 5,000, and the vast majority (84%) lived in the same regions as the species with populations under 1,000, creating the conditions for a domino effect.

The acceleration of the extinction crisis is certain because of the still fast growth in human numbers and consumption rates. In addition, species are links in ecosystems, and, as they fall out, the species they interact with are likely to go also. In the regions where disappearing species are concentrated, regional biodiversity collapses are likely occurring. Our results re-emphasise the extreme urgency of taking massive global actions to save humanity’s crucial life-support systems.

 Gerardo Ceballos,  View ORCID ProfilePaul R. Ehrlich, and Peter H. RavenPNAS first published June 1, 2020 https://doi.org/10.1073/pnas.1922686117

An aeroplane flies over a glacier in the Wrangell St Elias National Park in Alaska. Credit: Frans Lanting/Nat Geo Image CollectionPDF version

Politicians, economists and even some natural scientists have tended to assume that tipping points 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. 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.

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 summarised in the two recent IPCC Special Reports (published in 2018 and in September 2019 ) suggests that tipping points could be exceeded even between 1 and 2 °C of warming . Why is the world not reacting ?

Australia’s top climate scientist says “we are already deep into the trajectory towards collapse” of civilisation, which may now be inevitable because 9 of the 15 known global climate tipping points that regulate the state of the planet have been activated.

Australian National University emeritus professor Will Steffen told Voice of Action that there was already a chance we have triggered a “global tipping cascade” that would take us to a less habitable “Hothouse Earth” climate, regardless of whether we reduced emissions.

Steffen says it would take 30 years at best (more likely 40-60 years) to transition to net zero emissions, but when it comes to tipping points such as Arctic sea ice we could have already run out of time.

Evidence shows we will also lose control of the tipping points for the Amazon rainforest, the West Antarctic ice sheet, and the Greenland ice sheet in much less time than it’s going to take us to get to net zero emissions, Steffen says.


Nature defines 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). Thus:

E = R × U = p × D × τ / 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.

It is well argued 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.

Nature 575, 592-595 (2019)doi: 10.1038/d41586-019-03595-0


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