Séminaire

I will give an overview of three projects, all related to climate change in the Pacific.

1. Humans may have already increased the risk of major disruptions to Pacific rainfall (Power et al., Nature Communications, 2017)

Intermittent disruptions to rainfall patterns and intensity over the Pacific Ocean lasting up to 1 year – typically associated with El Niño-Southern Oscillation (ENSO) – have major impacts on severe weather, agricultural production, ecosystems, and disease within the Pacific, and in many countries beyond. The frequency with which major disruptions to Pacific rainfall occur has been projected to increase over the 21st century, in response to global warming caused by large 21st century greenhouse gas emissions. Here we use the latest generation of climate models to show that humans may have contributed to the major disruption that occurred in the real world during the late 20th century. We demonstrate that although marked and sustained reductions in 21st century anthropogenic greenhouse gas emissions can greatly moderate the likelihood of major disruption, elevated risk of occurrence appears locked in now, and for at least the remainder of the 21st century.

2. ENSO and associated climatic conditions around the world during the latter half of the 21st century (Power and Delage, Journal of Climate, 2018)

Increases in greenhouse gas emissions are expected to cause changes both in climatic variability in the Pacific linked to ENSO and in long-term average climate. While mean state and variability changes have been studied separately, much less is known about their combined impact or relative importance. Additionally, studies of projected changes in ENSO have tended to focus on changes in, or adjacent to, the Pacific. Here we examine projected changes in climatic conditions during El Niño years and in ENSO-driven precipitation variability in 36 CMIP5 models. The models are forced according to the RCP8.5 scenario in which there are large, unmitigated increases in greenhouse gas concentrations during the 21st century. We examine changes over much of the globe, including 25 widely spread regions defined in the IPCC special report SREX. We confirm that precipitation variability associated with ENSO is projected to increase in the tropical Pacific, consistent with earlier research. We also find that the enhanced
tropical Pacific variability drives ENSO-related variability increases in 19 SREX regions during DJF and in 18 during JJA. This externally forced increase in ENSO-driven precipitation variability around the world is on the order of 15%–20%. An increase of this size, although substantial, is easily masked at the regional level by internally generated multidecadal variability in individual runs. The projected changes in El Niño-driven precipitation
variability are typically much smaller than projected changes in the mean state in nearly all regions.

3. Strengthening Early Warning and Response Systems

The range of natural hazards faced by remote communities in the Solomon Islands is extraordinary. Climate model simulations suggest that global warming intensifies some of the hazards. I will outline the hazards, as well as aspects of life in remote communities, and the work we are doing – at the national, provincial and community level – to help people strengthen their ability to withstand future extreme events.

eric.guilyardi@locean-ipsl.upmc.fr