Key messages
- Unprecedented ocean warming since 2023 has broken sea surface temperature (SST) records, increasing scientific concerns about the potential consequences in large-scale processes in ocean and ocean–atmosphere interactions. New research on the physical impacts of global warming on 1) El Niño-Southern Oscillation (ENSO), potentially leading to more extreme El Niño events; and 2) the Atlantic Meridional Overturning Circulation (AMOC), potentially threatening its stability.
- The economic impacts of El Niño are far more severe than previously understood, with global income losses from past events adding up to trillions of US dollars. Moreover, the projected additional economic losses due to increased El Niño frequency and intensity resulting from global warming could be as high as US$84 trillion over the 21st century.
- AMOC could be closer to a critical slowdown, or even collapse, much earlier than previously estimated. The consequences for global climate, weather patterns, and human well-being would be severe.
- Future warming might be underestimated by current climate models due to biases and short observational records. Closing these gaps is crucial for improving predictions, conducting more robust risk assessments, and developing more effective adaptation strategies.
New research reveals two critical ocean-related risks. First, the global economic costs of El Niño impacts are much higher than previously thought, highlighting the vulnerability of our economic and social systems to ocean changes. Second, the AMOC, a key global ocean current system, may slow down or collapse sooner than earlier models projected. We feature these two ocean and ocean-atmosphere processes, as they illustrate that human well-being is highly sensitive to ocean variations and that significant oceanic changes are likely in the near term, posing substantial societal risks.
Since early 2023, global SST has reached unprecedented highs, breaking records not only in the tropical Pacific due to El Niño, but also in the North Atlantic, Gulf of Mexico, Caribbean, and Southern Ocean. Even after the 2023-2024 El Niño event faded, temperatures remained nearly 0.5°C above the 1991-2020 average through June of 2024 as of this writing. These changes in SST and the associated El Niño event have significant social and economic impacts.
Despite the physics of the El Niño–Southern Oscillation being well-understood, societies remain highly vulnerable to these events, with economic losses persisting for at least six years after an El Niño event. New research shows that the impacts of natural climate variations like El Niño are more than two orders of magnitude costlier to the global economy than previously thought, with past events causing trillions of dollars in losses. For example, the 1982–1983 and 1997–1998 El Niño events alone led to global income losses of US$4.1 and $5.7 trillion, respectively (Figure 5). Equally startling losses of US$2.1 trillion for the 1997–1998 and US$3.9 trillion for the 2015–2016 events are estimated by another study (Figure 3). For comparison, the gross domestic product (GDP) for Germany, the third largest economy in the world, was about US$4 trillion in 2022. The astounding costs of El Niño suggest that society is poorly adapted to present-day ocean temperature variability even without additional changes from global warming. Both studies suggest that macroeconomic losses grow dramatically with projected warming and El Niño changes. By one estimate, future El Niño events could cost the global economy US$84 trillion, the equivalent of the top 20 global economies combined, by the end of the 21st century.
Recent research shows that the AMOC is weakening due to planetary warming-driven changes and may decline further within this century. While the Intergovernmental Panel on Climate Change (IPCC) previously assessed that an AMOC collapse was unlikely this century, this evidence suggests it could happen sooner than expected. Taken together, past climate reconstructions, modern observations and model simulations, indicate the type of system behaviour and early warning signs suggestive of slowing circulation and potential collapse. If the AMOC weakens or collapses, it would have significant and complex impacts on global climate, sea levels, marine ecosystems and, subsequently, human societies. This calls for urgent monitoring and mitigation efforts.
To understand the climate risks we face this century, it is crucial to assess the reliability of climate models and the quality of observations. Most recent models suggest that El Niño events may become more intense even with strong mitigation efforts (though there are uncertainties due to biases in these models, particularly in predicting SST). Therefore, the actual warming could be even greater than previously predicted for the same emission scenario. Research should focus on bridging the gap between model results and observations such as SST, especially those used for predicting changes in El Niño and the AMOC. Improved models and longer, more accurate observational records are essential for reducing uncertainty and better preparing for future climate risks. To protect society from climate risks, science needs to address uncertainties in predictions. It is crucial that we have improved models, and properly understand the impact of rising SST. Policymakers should recognise that some risks remain beyond exact scientific prediction but have severe socio-economic and physical impacts, making it a critical consideration to inform risk assessments underpinning mitigation and adaptation plans.
Policy implications
- Although El Niño events are part of the natural climate variability and occur at predictable intervals, the magnitude and persistence of the economic losses they cause is indicative of how poorly adapted most economies are to such impacts. El Niño impacts, such as amplified droughts, floods, and heat extremes, mirror the broader consequences of global warming. Strengthening adaptive capacity and resilience to El Niño events can also enhance overall preparedness for climate change.
- Scientific evidence suggesting more intense ENSO events due to global warming, and their potential economic impacts, should alert governments on the importance of incorporating this knowledge into the Framework for Global Climate Resilience (FGCR). In particular, this should be reflected in defining concrete targets, progress indicators, and means of implementation, expected by 2025. It is especially important for tropical countries economically dependent on their agricultural sector to prioritise the inclusion of ENSO-related impacts on their National Adaptation Plans (NAPs).
- The projected macroeconomic toll of rising ENSO impacts under current trends of global warming should add a sense of urgency to close the adaptation finance gap, given the risk of higher economic losses further limiting the capacity for adaptation investments.
- The severe costs of El Niño highlight the potential for even greater social and economic disruption if the AMOC slows or collapses, which would push the climate into an unprecedented state. However, the likelihood and timing of such an event are uncertain.
The UNFCCC could request the IPCC to produce a report on “high-impact, low-likelihood” phenomena, including climate tipping points, to provide clear scientific guidance for policymakers. - Investments are needed to strengthen long-term ocean monitoring capabilities, including key indicators relevant to ENSO and AMOC; improve climate models with coupled ocean–atmosphere dynamics to reduce uncertainties; enhance regional climate projections; and promote interdisciplinary integration, including socio-economic analyses.
