The Paris Agreement set an ambitious goal of limiting global warming to well below 2°C above pre-industrial levels, with the aim of pursuing 1.5°C. However, on current emissions trajectories, there is a real possibility that The global average temperature (GMT) will temporarily exceed the 1.5°C limit. A new study, based on an analysis of relevant future emission scenarios, warns that permanently exceeding this limit significantly increases the likelihood of triggering climatic tipping elements.

What are climatic tipping points?

Climatic tipping points are complex subsystems of the Earth that can exhibit nonlinear, often abrupt, transitions in response to global warming. This means that even a small increase in GMT can trigger a large qualitative change in these systems. A characteristic feature of these changes is often hysteretic behavior, meaning that even lowering the temperature to its original level may not reverse the initiated change. These transitions are driven by self-reinforcing feedback loops.

Major fault lines with potential planetary impacts include:

• Greenland Ice Sheet (GIS)
• West Antarctic Ice Sheet (WAIS)
• Atlantic Meridional Circulation (AMOC)
• Amazon Rainforest (AMAZ)

These elements are interconnected, and interactions can stabilize or worsen their dynamics, potentially leading to tipping cascades. The consequences of triggering tipping points would be severe, including a rise in global sea levels of several meters, ecosystem collapse, widespread biodiversity loss, and substantial changes in the global distribution of heat and precipitation.

Risks associated with exceeding 1.5°C

The study used a stylized Earth system model including four interconnected fault elements (GIS, WAIS, AMOC, AMAZ) to assess the risks under different emission scenarios. It found that a scenario replicating current (2020) policies risks 45% risk of triggering at least one fault element (median estimate, range 23–71%). In the long term (50,000 years) this risk increases to 76% (median estimate, range 39–98%).

Analysis of different scenarios showed that the risk of triggering tipping points by 2300 increases with each additional 0.1°C of peak temperature rise above 1.5°CThis increase is significantly accelerates at peak warming above 2.0°C, with an increase in risk of more than 3% for every 0.1°C above 2.5°C. This underlines the importance of the Paris target of keeping warming “well below 2°C”, even in the event of a temporary exceedance of 1.5°C.

In the medium term (to 2300), the highest risk is posed by faster fault elements such as AMOC (overturning period 15–300 years) and AMAZ (50–200 years). In the long term, the risks are highest for AMOC and WAIS (500–13,000 years).

The key role of net zero emissions

The study highlights that Achieving and maintaining at least net zero greenhouse gas (NZGHG) emissions by 2100 is paramount to minimizing the risk of triggering tipping points in the long termScenarios that achieve and maintain the NZGHG lead to significantly lower probabilities of triggering tipping points compared to scenarios that do not achieve the NZGHG, or achieve it only temporarily.

While the peak temperature at the exceedance is decisive for medium-term risks, in the long term, the stabilization temperature becomes decisive, which is determined by long-term emission behavior. Scenarios that return to a median warming below 1.5°C by 2100 and then maintain NZGHG (such as SP-NZGHG, Neg-NZGHG, Neg-OS-0C) will keep long-term medium risks in a very unlikely range (<12% upper limit). In contrast, stabilising at 1.5°C without prior exceedance (the “Ref-1p5” scenario) leads to a risk of more than 50% in the long term.

Findings suggest that stabilizing global temperatures at or around 1.5°C in the long term not enough to limit the risk of breaking pointsTo effectively minimize this risk, the study suggests that temperatures should be brought back down in the long term. below 1 °C compared to pre-industrial levels.

The study clearly shows that current policies and nationally determined commitments (NDCs) are not sufficient to minimize the risks associated with climate tipping points. Even if temperatures are returned to 1.5°C or below after 2100, the risk remains high if significant exceedances occur. Every 0.1°C of additional excess above 1.5°C increases the risk.

To effectively limit the risks, it is essential to keep warming well below 2°C under all circumstances, even if it temporarily exceeds 1.5°C. Beyond peak warming, achieving and Maintaining net zero greenhouse gas emissions is key to limiting long-term risks by keeping temperatures below 1.5°C and below. The 1.5°C target of the Paris Agreement should be seen as an upper limit, not a safe level, for planetary stability in terms of tipping points. A more substantial and urgent mitigation effort is needed that goes beyond pledges and leads to the implementation of domestic policies. Spring

The entire study was published in the journal Nature Communications .

Glossary of key terms

• Climatic tipping points: Complex subsystems of the Earth system that may undergo sudden and often irreversible changes in state in response to global warming.
• Global Mean Temperature (GMT): Average temperature of the Earth's surface and oceans.
• Paris Agreement: An international treaty aimed at keeping global warming well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C.
• Exceeding: A situation where global temperature temporarily exceeds a target threshold (e.g. 1.5°C), even if it later decreases.
• Zero Net Greenhouse Gas Emissions (NZGHG): Achieving a balance between anthropogenic emissions of greenhouse gases and anthropogenic removals of these gases from the atmosphere over a certain period of time.
• Hysteresis: A property of a system where its state depends not only on current conditions but also on its previous history, leading to the potential for irreversible change.
• Greenland Ice Sheet (GIS): The large ice sheet covering Greenland, which is sensitive to warming, and its melting contributes to rising sea levels.
• West Antarctic Ice Sheet (WAIS): A large ice sheet in Antarctica that is particularly susceptible to accelerated melting due to interactions between ice streams and warm ocean water.
• Atlantic Meridional Overturning Circulation (AMOC): A large system of ocean currents in the Atlantic Ocean that plays a key role in the distribution of heat and can be destabilized by the influx of freshwater from melting ice sheets.
• Amazon Rainforest (AMAZ): A vast rainforest in South America that is a significant carbon reservoir and whose stability is affected by changes in precipitation patterns and deforestation.
• Fold-bifurcation models: Simplified conceptual models used to simulate the behavior of tipping points that exhibit hysteresis properties when crossing a critical threshold.
• Monte Carlo ensemble approach: A method based on repeated random sampling to estimate the probabilities of outcomes of a system with many variables with uncertainty.
• Carbon Dioxide Removal (CDR): Technologies and methods aimed at removing CO2 from the atmosphere.
• Nationally Determined Contributions (NDCs): Commitments to reduce greenhouse gas emissions made by individual countries under the Paris Agreement.
• Pre-industrial levels: A reference period (usually 1850–1900) used to compare global temperature increases before the significant impact of industrialization.