Pacific climate variability and its regional impacts in warmer, stabilised climates

Abstract

The El Niño Southern Oscillation (ENSO) in the tropical Pacific is the main mode of inter-annual climate variability and a key driver of regional climate across much of the globe. Future changes in its behaviour are highly policy-relevant as they would have large impacts across many regions and significantly affect ecosystems and livelihoods. In this presentation, we explore how ENSO variability evolves in multi-century experiments under fixed atmospheric concentrations of greenhouse gases, where global mean surface temperatures are slowly stabilising.We show how ENSO variability and its teleconnections change in a range of climate models and experimental designs. Idealised projections under fixed atmospheric concentrations of greenhouse gases across multiple levels of global warming, from 1.5°C to 5°C, are evaluated for the UK Earth System Model 1 alongside abrupt forcing experiments with the Community Earth System Model 1. We also include closely related experimental designs, such as emission-driven stabilisation experiments with ACCESS-ESM-1.5. The differences in how ENSO and its teleconnections respond to further warming in long, multi-century experiments under constant or slowly declining forcing conditions are compared and contrasted to the expected ENSO changes in rapidly warming, transient climate change projections. These differences are important to understand in the context of ambitious mitigation scenarios that aim to stabilise global temperatures at, or below, the Paris Agreement temperature targets. Preliminary results suggest that future ENSO variability is model dependent, but withing a single model framework independent of the level at which warming is stabilised at.