Attribution of the 2015 record high sea surface temperatures over the central equatorial Pacific and tropical Indian Ocean

Abstract

This study assessed the anthropogenic contribution to the 2015 record-breaking high sea surface temperatures (SSTs) observed in the central equatorial Pacific and tropical Indian Ocean. Considering a close link between extreme warm events in these regions, we conducted a joint attribution analysis using a fraction of attributable risk approach. Probability of occurrence of such extreme anomalies and long-term trends for the two oceanic regions were compared between CMIP5 multi-model simulations with and without anthropogenic forcing. Results show that the excessive warming in both regions is well beyond the range of natural variability and robustly attributable to human activities due to greenhouse gas increase. We further explored associated mechanisms including the Bjerknes feedback and background anthropogenic warming. It is concluded that background warming was the main contribution to the 2015 extreme SST event over the central equatorial Pacific Ocean on a developing El Niño condition, which in turn induced the extreme SST event over the tropical Indian Ocean through the atmospheric bridge effect.

Attributing the U.S. Southwest's Recent Shift Into Drier Conditions

“…Despite the broad consensus on the relative roles of internal variability and anthropogenic forcing, the exact quantification of the individual factors contributing to the U.S. SW's recent shift into drier conditions remains challenging (Schubert et al, 2016). For example, it seems likely that tropical sea surface temperatures (SSTs) during recent decades were influenced to some extent by GHG forcing (e.g., Park et al, 2017), although the spatial fingerprint of GHG forcing on tropical SSTs and precipitation appears distinct from the observed trend over recent decades (Deser & Phillips, 2009). Further, uncertainties remain with regard to observed SST trends (Coats & Karnauskas, 2017;Deser et al, 2010).…”

High-impact marine heatwaves attributable to human-induced global warming

“…Understanding whether and by how much anthropogenic climate change has contributed to the intensity and likelihood of extreme events is of substantial scientific and public interest-for example, to motivate efforts to limit global warming. Atmospheric heatwaves, droughts, and floods are routinely attributed to climate change (18,19); however, there have been only a few attempts to attribute MHWs to climate change (6,(20)(21)(22)(23)(24)(25). These publications have differed strongly in their methodologies, in their framings of the attribution question, and in their treatments of the uncertainties of the attribution process, which makes their results difficult to compare and interpret (18,26).…”

Early and Extreme Warming in the South China Sea During 2015/2016: Role of an Unusual Indian Ocean Dipole Event

“…The narrower cooling anomaly over the MC in 2015 compared with other El Niño events was largely attributed to an unusual pIOD event, which made the western boundary of the cooling anomaly move eastward. Previous studies gave some explanations that the unusual pIOD event could be largely attributed to the interdecadal change (Zhang et al, 2018) and long‐term anthropogenic background warming (Park et al, 2017; Roxy et al, 2014) but need further research. Although the impact of Indian Ocean on the relationship between ENSO and the Austral‐Asian climate have been noticed (Zhu, 2018; Zhu et al, 2014), the oceanic processes and their feedbacks on climate still remain unclear.…”

“…The narrower cooling anomaly over the MC in 2015 compared with other El Niño events was largely attributed to an unusual pIOD event, which made the western boundary of the cooling anomaly move eastward. Previous studies gave some explanations that the unusual pIOD event could be largely attributed to the interdecadal change (Zhang et al, 2018) and long-term anthropogenic background warming (Park et al, 2017;Roxy et al, 2014) but need further research.…”