Scientists Say Climate Models Cannot Yet Predict El Nino Behaviour Under Warming

Mariam Zachariah, research associate at Imperial College London, says current climate models show systematic biases in simulating El Nino events, leaving key questions about future frequency, intensity, and spatial patterns unanswered. The IPCC's Sixth Assessment Report found no clear evidence of long-term trends in El Nino-Southern Oscillation behaviour that can be distinguished from natural variability.

Scientists track climate change's influence on ENSO by examining sea surface temperatures, atmospheric circulation, and the frequency of El Nino and La Nina events in observational data and climate model simulations. Some studies suggest anthropogenic warming may be driving more frequent El Nino events in recent decades, but natural internal variability makes attribution difficult. A recent large-ensemble modelling study found that the observed rise in multi-year La Nina events since the 1960s is mainly driven by internal variability, with external forcing playing only a minor role.

Current climate models often show biases in key features including circulation patterns and sea surface temperature distribution across the Pacific, causing them to simulate El Nino teleconnections to varying extents across different regions. The IPCC AR6 concluded that while ENSO-related rainfall variability is expected to increase in the long term — meaning El Nino and La Nina could produce stronger rainfall extremes in some regions — near-term changes are likely to continue to be dominated by natural variability.

Key unresolved research questions include whether El Nino events will become stronger or more frequent under future warming, how their spatial patterns may shift, and how their global impacts will change. Addressing these gaps requires longer and higher-quality observational records, improved climate models with reduced systematic biases, and better understanding of complex ocean-atmosphere feedbacks in the tropical Pacific. For India, where El Nino events have historically been associated with weaker monsoon rainfall, resolving these uncertainties has direct implications for food and water security planning.

Key figure — 1.5°C and 2°C warming thresholds examined in projections