The triple-dip La Niña was key to Earth’s extreme heat uptake in 2022-2023

Recent observations reveal a surge in Earth's energy uptake in 2022/23. Despite its pivotal role in the striking global surface temperature rise and widespread climate extremes observed by early 2024 1,2, its attribution is hampered by the lack of understanding on the role of internal climate variability on the Earth’s energy imbalance. Here, through analyzing multi-model climate simulations, we show that the 2022/23 extreme Earth’s energy uptake is tied to the transition from the three-year La Niña 3,4,5,6 to the strong 2023/24 El Niño. We find that simulation samples with extreme global energy uptake systematically accompany preceding multi-year La Niña and subsequent El Niño, consistent with observations. These samples also replicate the dominant contribution of the shortwave radiation anomaly to the net energy imbalance and spatial distributions of radiation and atmospheric circulation anomalies organized by El Niño-Southern Oscillation. Our additional sampling analyses with ENSO transition confirm the major role of the La Niña-to-El Niño sequence on the enhanced energy uptake, with the key importance of multi-year persistence in preceding La Niña. Our finding illustrates the striking influence of internal climate variability on Earth's energy budget in addition to anthropogenic forcing and underscores their significance in past and future global climate extremes.