Continued increase of extreme El Niño frequency long after 1.5 °C warming stabilization

• Published in: Nature climate change Vol. 7; no. 8; pp. 568 - 572
• Main Authors: Wang, Guojian, Cai, Wenju, Gan, Bolan, Wu, Lixin, Santoso, Agus, Lin, Xiaopei, Chen, Zhaohui, McPhaden, Michael J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.08.2017; Nature Publishing Group
• Subjects: 704/106/35/823; 704/106/694; 704/106/829/2737; Agricultural ecosystems; Agriculture; Agronomy; Climate; Climate Change; Climate Change/Climate Change Impacts; Climate models; Climatology; Ecosystems; El Nino; El Nino events; El Nino phenomena; Environment; Environmental Law/Policy/Ecojustice; Equatorial regions; Global temperatures; Intercomparison; La Nina; La Nina events; letter; Mean temperatures; Ocean currents; Paris Agreement; Public health; S phase; Temperature effects; Thermocline; Weather patterns
• ISSN: 1758-678X; 1758-6798
• DOI: 10.1038/nclimate3351

CMIP5 simulations reveal that the frequency of extreme El Niño events doubles under the 1.5 °C Paris target, and continues to increase long after global temperatures stabilize due to emission reductions. Extreme La Niña events, however, see little change at either 1.5 °C or 2 °C warming. The Paris Agreement aims to constrain global mean temperature (GMT) increases to 2 °C above pre-industrial levels, with an aspirational target of 1.5 °C. However, the pathway to these targets 1 , 2 , 3 , 4 , 5 , 6 and the impacts of a 1.5 °C and 2 °C warming on extreme El Niño and La Niña events—which severely influence weather patterns, agriculture, ecosystems, public health and economies 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 —is little known. Here, by analysing climate models participating in the Climate Model Intercomparison Project’s Phase 5 (CMIP5; ref.  17 ) under a most likely emission scenario 1 , 2 , we demonstrate that extreme El Niño frequency increases linearly with the GMT towards a doubling at 1.5 °C warming. This increasing frequency of extreme El Niño events continues for up to a century after GMT has stabilized, underpinned by an oceanic thermocline deepening that sustains faster warming in the eastern equatorial Pacific than the off-equatorial region. Ultimately, this implies a higher risk of extreme El Niño to future generations after GMT rise has halted. On the other hand, whereas previous research suggests extreme La Niña events may double in frequency under the 4.5 °C warming scenario 8 , the results presented here indicate little to no change under 1.5 °C or 2 °C warming.