It is now almost certain that 2023 will be the hottest year ever recorded by humans, possibly the hottest year in at least 125,000 years. Many temperature records were broken, with global average temperatures significantly exceeding 1.5°C in some periods. Sea ice loss in Antarctica is increasing at an alarming rate, along with many other indicators of rapid climate change. Does this mean that 2023 is the year when the climate will become much more dangerous?

Most people think that if a system, say someone’s body, part of the ecosystem or climate system, is subjected to stress, it will react in a fairly predictable way, doubling the pressure, doubling the impact, etc. waits. This is true in many cases, but not always. Sometimes a stressed system changes regularly (or “linearly”) up to a certain point, but beyond that much larger or more abrupt changes may be noted.

An example of such “non-linear” changes are “tipping points,” which occur when a system crosses a threshold beyond which change becomes self-sustaining. This means that even if the initial pressure is reduced, changes will continue until the system sometimes reaches a completely different state.

Imagine rolling a boulder up a hill. It requires a lot of energy. If the energy supply stops, the ball will bounce back. But once the top of the hill is reached and the stone is balanced at the top, a gentle push, perhaps even a gust of wind, may be enough to send the stone rolling to the other side.

The climate system has many potential tipping points, such as ice sheets disappearing or dense tropical forests becoming much drier and more open. Once they reach a critical point, it is very difficult or even impossible to restore these systems.

We, along with 200 other scientists from around the world, have published a new Global Report on milestones at the COP28 UN climate talks in Dubai. Our report reveals scientific findings on “negative” tipping points in the Earth system that could harm both nature and people, as well as potential “positive” societal tipping points that could accelerate action for sustainable development.

Here, we examine key messages from the report’s chapters on turning points in the Earth system, their impacts on humans, and how to manage these changes.

Tipping points in the air, on land and at sea

By analyzing scientific evidence of past and present changes and considering the predictions of computer models, we have identified more than 25 tipping points in the Earth system. Six of these are located in ice-covered parts of the planet (the “cryosphere”), including the collapse of massive ice sheets in Greenland and various parts of Antarctica, as well as local collapse of glaciers and melting of permafrost.

Sixteen of them are in the “biosphere”, that is, the totality of all ecosystems on Earth, including the mass extinction of trees in parts of the Amazon and northern boreal forests, degradation of savannas and drylands, nutrient overload of lakes, mass extinction of coral reefs. and many mangroves and seagrasses are dying.

Finally, we identify four potential tipping points in ocean-atmosphere circulation, including the collapse of deep ocean mixing in the North Atlantic and the Southern Ocean around Antarctica and the disruption of the West African monsoon.

Human activities are already pushing some to breaking points. Exact thresholds are unknown, but at today’s 1.2°C of global warming, large-scale loss of warm-water coral reefs is already likely, while tipping is possible in four other vital climate systems. These are the collapse of the Greenland and West Antarctic ice sheets, the collapse of the North Atlantic circulation, and widespread local melting of permafrost.

While some temperatures above 1.5°C become likely, other systems such as mangroves, seagrasses and parts of boreal forests begin to become vulnerable. Some systems may also lower or reduce warming thresholds due to other factors, such as deforestation in the Amazon.

The consequences of passing these milestones can be difficult to grasp. For example, if parts of the Amazon rainforest die, countless species will disappear and warming will worsen as billions of tonnes of carbon currently locked in trees and soil will be released into the atmosphere.

It could cause an economic impact of trillions of dollars in the region and expose millions of people to extreme heat. Given the magnitude of tipping point risks, you might assume that economic forecasts of climate change would include them. Unfortunately, most assessments effectively ignore tipping point risks. This is perhaps the most frightening conclusion of the new report.

Human societies may tend to do much worse

There is also the potential for negative spillovers, causing further financial instability, displacement, conflict, or polarization in human societies. This could hinder our efforts to limit further tipping points in the Earth system and could even lead to a transition to a social system characterized by greater authoritarianism, hostility, and alienation, which could derail the transition to sustainability altogether.

Another risk is that many of Earth’s toppling systems will interact in ways that destabilize each other. In the worst-case scenario, failure of one system increases the likelihood that connected systems will also fail. This can result in a “cascade of toppling overs” like falling dominoes.

The Global Tipping Points Report makes clear that climate change is a key driver of many of these tipping points and that the risk of exceeding these tipping points can be reduced by urgently reducing greenhouse gas emissions to zero (“positive tipping points” could accelerate this).

To avoid tipping points in the biosphere, we will need to rapidly reduce habitat loss and pollution while supporting ecological recovery and sustainable livelihoods. Ambitious new management approaches are needed. Our report recommends that international organizations, such as the UN climate negotiations, urgently start considering tipping points. Their understanding of dangerous climate change needs serious updating.