high-impact risks
- The IPCC AR6 acknowledges that many human-caused changes, especially to the ocean, ice sheets and global sea level, are high risk and irreversible for centuries to millennia – some of them involving tipping processes (see Background) – and that these changes are key to a comprehensive risk assessment.
- Significant destabilization of several key climate tipping elements is already being observed today.
- In many cases, the dominant driver of this destabilization is global warming. But direct human influence on land cover change, such as degradation and active deforestation of the Amazon rainforest, can play an equal or even stronger role.
- Some tipping elements, for example melting ice sheets and changes to ocean currents, but also deforestation of rainforests, influence each other. Recent research indicates that interactions among tipping elements can ultimately cause shifts to happen at lower levels of global warming than anticipated.
- Earth’s temperature response to doubling the levels of carbon dioxide in the atmosphere is now better understood. While previous IPCC assessments have used an estimated range of 1.5–4.5°C, recent research now suggests a narrower range of 2.3–4.5°C.
- This means that moderate emissions reduction scenarios are less likely to meet the Paris temperature targets than previously anticipated.
- Improved regional scale models provide better information about heavy rainfall events and hot and cold extremes, offering new opportunities for water resource management.
- Regional climate predictions can now be made up to a decade ahead with higher skill than previously thought possible.
The IPCC has, over the past two decades, continually strengthened their risk assessment concerning so-called “large scale singular events”. Stronger than before, the most recent report (IPCC AR6 WG I) recognizes risks from non-linear changes in tipping elements in the climate system (see Background) as well as irreversible long-term commitments, as possible outcomes of anthropogenic climate change and direct human pressure. Changes in tipping elements are particularly afflicted with high uncertainties (in terms of likelihood or timing, or both), but also associated with large risks for societies and ecosystems. These high-impact, high uncertainty risks are termed “low-likelihood, high-impact outcomes” in IPCC AR6 – even if, as the authors explicitly state, probabilities are not necessarily known to be low, but simply not well constrained. The consequences are large, long term and associated with existential risks for nature and societies.
Among these risks associated with selected tipping elements, as discussed in the Spotlight, are
- from an increased disintegration of the ice sheets: a catastrophic 2 metres of sea level rise by 2100 and even
more devastating 5 metres by 2150 (which are explicitly not ruled out by the IPCC AR6 WGI, 9.6.3.3). In the long term, we are committed to a similar degree of sea-level rise, for instance of 2-6 metres in the two millennia following peak 2°C warming (IPCC AR6 WGI, 9.6.3.5 and Cross Chapter Box 12.1); - from a slowdown or shutdown of the major Atlantic Ocean circulation: abrupt changes in weather patterns, for example in Europe, which are currently highly dependent on the inflow of heat from the Atlantic Ocean circulation;
- from a shift in the Atlantic circulation: shifts of water cycles affecting several monsoon systems, and specifically a heat redistribution that alters precipitation patterns over the Amazon, although it remains unclear whether overall rainfall will be increased or reduced;
- from a climate regime shift in the Amazon: a feedback to regional climate conditions (loss of rainforest vegetation changes the moisture exchange with the air, for example), and a potential permanent loss of the Amazon basin as a major carbon sink.
A number of recently published research results confirm and refine the IPCC’s assessment, and furthermore indicate that several climate subsystems are already showing signs of losing stability today and are moving towards critical thresholds (tipping points, see Spotlight). In addition to the risks from individual tipping processes, science has identified an overarching, additional layer of risk: tipping elements may be involved in domino-type cascades – with one tipping process (for example Greenland ice loss) triggering another one (in that case a slowdown of the major Atlantic Ocean circulation due to meltwater intrusion). Therefore, in addition to the risk from each tipping element alone, their interaction exacerbates the situation and compounds the overall risk – tipping could happen more easily (at lower global temperatures) than if they were separated.
The IPCC has, over the past two decades, continually strengthened their risk assessment concerning so-called “large scale singular events”. Stronger than before, the most recent report (IPCC AR6 WG I) recognizes risks from non-linear changes in tipping elements in the climate system (see Background) as well as irreversible long-term commitments, as possible outcomes of anthropogenic climate change and direct human pressure. Changes in tipping elements are particularly afflicted with high uncertainties (in terms of likelihood or timing, or both), but also associated with large risks for societies and ecosystems. These high-impact, high uncertainty risks are termed “low-likelihood, high-impact outcomes” in IPCC AR6 – even if, as the authors explicitly state, probabilities are not necessarily known to be low, but simply not well constrained. The consequences are large, long term and associated with existential risks for nature and societies.
Among these risks associated with selected tipping elements, as discussed in the Spotlight, are
- from an increased disintegration of the ice sheets: a catastrophic 2 metres of sea level rise by 2100 and even
more devastating 5 metres by 2150 (which are explicitly not ruled out by the IPCC AR6 WGI, 9.6.3.3). In the long term, we are committed to a similar degree of sea-level rise, for instance of 2-6 metres in the two millennia following peak 2°C warming (IPCC AR6 WGI, 9.6.3.5 and Cross Chapter Box 12.1); - from a slowdown or shutdown of the major Atlantic Ocean circulation: abrupt changes in weather patterns, for example in Europe, which are currently highly dependent on the inflow of heat from the Atlantic Ocean circulation;
- from a shift in the Atlantic circulation: shifts of water cycles affecting several monsoon systems, and specifically a heat redistribution that alters precipitation patterns over the Amazon, although it remains unclear whether overall rainfall will be increased or reduced;
- from a climate regime shift in the Amazon: a feedback to regional climate conditions (loss of rainforest vegetation changes the moisture exchange with the air, for example), and a potential permanent loss of the Amazon basin as a major carbon sink.
A number of recently published research results confirm and refine the IPCC’s assessment, and furthermore indicate that several climate subsystems are already showing signs of losing stability today and are moving towards critical thresholds (tipping points, see Spotlight). In addition to the risks from individual tipping processes, science has identified an overarching, additional layer of risk: tipping elements may be involved in domino-type cascades – with one tipping process (for example Greenland ice loss) triggering another one (in that case a slowdown of the major Atlantic Ocean circulation due to meltwater intrusion). Therefore, in addition to the risk from each tipping element alone, their interaction exacerbates the situation and compounds the overall risk – tipping could happen more easily (at lower global temperatures) than if they were separated.
Global warming and direct human pressure impose significant changes to key components of the climate system. Next to gradual changes that are proportional to the level of global warming, some components face the risk of undergoing dramatic and non-linear transitions at varying timescales, often without a chance to turn back to normal for a long time. These parts of the climate system are called tipping elements.
The actual transition can unfold over centuries to millennia (when ice sheets melt or disintegrate), over decades to centuries (when ocean currents slow down or reshape) or years to decades (especially when direct human interference pushes a transition, like deforestation in the Amazon rainforest).
The challenge with tipping elements is that we do not know exactly at what levels of global warming thresholds will be passed, given the complex nature of interactions. The danger is that once the thresholds are crossed there may be no realistic turning back. Even if levels of global temperature are brought back down again, self-reinforcing effects can drive further ice loss, forest die-back or other shifts, until the system can no longer be recognized.
Global warming and direct human pressure impose significant changes to key components of the climate system. Next to gradual changes that are proportional to the level of global warming, some components face the risk of undergoing dramatic and non-linear transitions at varying timescales, often without a chance to turn back to normal for a long time. These parts of the climate system are called tipping elements.
The actual transition can unfold over centuries to millennia (when ice sheets melt or disintegrate), over decades to centuries (when ocean currents slow down or reshape) or years to decades (especially when direct human interference pushes a transition, like deforestation in the Amazon rainforest).
The challenge with tipping elements is that we do not know exactly at what levels of global warming thresholds will be passed, given the complex nature of interactions. The danger is that once the thresholds are crossed there may be no realistic turning back. Even if levels of global temperature are brought back down again, self-reinforcing effects can drive further ice loss, forest die-back or other shifts, until the system can no longer be recognized.
Climate negotiators and decision makers on all levels – international, national and local, need to:
- be aware of high-impact risks from climate tipping elements, and incorporate the remaining uncertainties about likelihood and timing in their risk assessments;
- apply the precautionary principle and aim for more ambitious climate protection, rather than the reverse. This is analogous to the approach to other societal risks, like that of a catastrophic nuclear accident, where large safety margins are prudent.
At a local level, where direct human influence has the potential to initiate tipping processes, for instance in parts of the Amazon rainforest, actors must take all possible measures to avoid tipping risks.
Climate negotiators and decision makers on all levels – international, national and local, need to:
- be aware of high-impact risks from climate tipping elements, and incorporate the remaining uncertainties about likelihood and timing in their risk assessments;
- apply the precautionary principle and aim for more ambitious climate protection, rather than the reverse. This is analogous to the approach to other societal risks, like that of a catastrophic nuclear accident, where large safety margins are prudent.
At a local level, where direct human influence has the potential to initiate tipping processes, for instance in parts of the Amazon rainforest, actors must take all possible measures to avoid tipping risks.
[+]
| ↑1, ↑4 | Smith, J. B., Schneider, S. H., Oppenheimer, M., Yohe, G. W., Hare, W., Mastrandrea, M. D.; Patwardhan, A., Burton, I., Corfee-Morlot, J., Magadza, C. H. D., Füssel, H.-M., Pittock, A. B., Rahman, A., Suarez, A., and van Ypersele, J.-P. 2009): Assessing dangerous climate change through an update of the Intergovernmental Panel on Climate Change IPCC) “reasons for concern”. In PNAS, 106 (11), pp. 4133–4137. DOI: 10.1073/pnas.0812355106. |
|---|---|
| ↑2, ↑5 | IPCC (2013): Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovern-mental Panel on Climate Change. Stocker, T. F., Qin, D., Plattner, G.-K., Tignor, M., Allen, S. K., Boschung, J., Nauels, A., Xia, Y., Bex, V., and Midgley, P. M. (eds.). Cambridge University Press, Cambridge. |
| ↑3, ↑6 | IPCC (2018): Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above preindustrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. Masson-Delmotte, V., Zhai, P., Pörtner, H.-O., Roberts, D., Skea, J., Shukla, P. R., Pirani, A., Moufouma-Okia, W., Péan, C., Pidcock, R., Connors, S., Matthews, J. B. R., Chen, Y., Zhou, X., Gomis, M. I., Lonnoy, E., Maycock, T., Tignor, M., and Waterfield, T. eds.). In Press. |
[+]
| ↑1, ↑4 | Smith, J. B., Schneider, S. H., Oppenheimer, M., Yohe, G. W., Hare, W., Mastrandrea, M. D.; Patwardhan, A., Burton, I., Corfee-Morlot, J., Magadza, C. H. D., Füssel, H.-M., Pittock, A. B., Rahman, A., Suarez, A., and van Ypersele, J.-P. 2009): Assessing dangerous climate change through an update of the Intergovernmental Panel on Climate Change IPCC) “reasons for concern”. In PNAS, 106 (11), pp. 4133–4137. DOI: 10.1073/pnas.0812355106. |
|---|---|
| ↑2, ↑5 | IPCC (2013): Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovern-mental Panel on Climate Change. Stocker, T. F., Qin, D., Plattner, G.-K., Tignor, M., Allen, S. K., Boschung, J., Nauels, A., Xia, Y., Bex, V., and Midgley, P. M. (eds.). Cambridge University Press, Cambridge. |
| ↑3, ↑6 | IPCC (2018): Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above preindustrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. Masson-Delmotte, V., Zhai, P., Pörtner, H.-O., Roberts, D., Skea, J., Shukla, P. R., Pirani, A., Moufouma-Okia, W., Péan, C., Pidcock, R., Connors, S., Matthews, J. B. R., Chen, Y., Zhou, X., Gomis, M. I., Lonnoy, E., Maycock, T., Tignor, M., and Waterfield, T. eds.). In Press. |
10
Costs of climate change mitigation can be justified by the multiple immediate benefits to the health of humans and nature
6
Supporting household behaviour changes is a crucial but often overlooked opportunity for climate action
7
Political challenges impede effectiveness of carbon pricing
8
Nature-based solutions are critical for the pathway to Paris—but look at the fine print
9
Building resilience of marine ecosystems is achievable by climate-adapted conservation and management, and global stewardship
3
Megafires — Climate change forces fire extremes to reach new dimensions with extreme impacts
5
Global climate action must be just
Supporting household behaviour changes is a crucial but often overlooked opportunity for climate action
6
7
Political challenges impede effectiveness of carbon pricing
Nature-based Solutions are critical for the pathway to Paris – but look at the fine print
8
9
Building resilience of marine ecosystems is achievable by climate-adapted conservation and management, and global stewardship
Costs of climate change mitigation can be justified by the multiple immediate benefits to the health of humans and nature
10
1
Stabilizing at 1.5°C warming is still possible, but immediate and drastic global action is required
Rapid growth in methane and nitrous oxide emissions put us on track for 2.7°C warming
2
10 New Insights in Climate Science
A year of climate-related science in review
Each year we consult researchers and carry out a horizon scan in fields related to climate change on what the latest findings and most important new emerging fields are. We summarize this in 10 important scientific insights, and the result has always been a rich and valuable scientific synthesis for policy and society at large, a testament to the ever-expanding and improving knowledge of our planetary climate systems and the interactions with the human world.Extras
Acknowledgements
The full authoring team and other contributors are listed here. The making of this report has been led by Future Earth, The Earth League and the World Climate Research Programme (WCRP). We also gratefully acknowledge support from Arizona State University (ASU), GERICS Climate Service Center Germany (an institution of Helmholtz-Zentrum Hereon),
We acknowledge the work of the following individuals in their respective capacities:
Produced by: Future Earth, The Earth League, Azote, and the World Climate Research Programme
Website, graphics and publication design: Cultivate Communications, Azote
10 New Insights in Climate Science
A year of climate-related science in review
Each year we consult researchers and carry out a horizon scan in fields related to climate change on what the latest findings and most important new emerging fields are. We summarize this in 10 important scientific insights, and the result has always been a rich and valuable scientific synthesis for policy and society at large, a testament to the ever-expanding and improving knowledge of our planetary climate systems and the interactions with the human world.Extras
Acknowledgements
The full authoring team and other contributors are listed here. The making of this report has been led by Future Earth, The Earth League and the World Climate Research Programme (WCRP). We also gratefully acknowledge support from Arizona State University (ASU), GERICS Climate Service Center Germany (an institution of Helmholtz-Zentrum Hereon),
We acknowledge the work of the following individuals in their respective capacities:
Produced by: Future Earth, The Earth League, Azote, and the World Climate Research Programme
Website, graphics and publication design: Cultivate Communications, Azote