Our Common Future Under Climate Change

International Scientific Conference 7-10 JULY 2015 Paris, France

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Tuesday 7 July - 14:30-16:00 UNESCO Fontenoy - ROOM XII

L1.5 - Climate variability, change and vulnerability in the Pacific, Indian and Southern Oceans

Large Parallel Session

Chair(s): E. Guilyardi (LOCEAN/IPSL, Paris, France)

Convener(s): V. Sarma (National Institute of Oceanography, Visakhapatnam, India), B. Pelletier (Grand Observatoire du Pacifique Sud GOPS, Nouméa, New Caledonia), J.B. Sallée (Sorbonne Universités, Paris, France), M. Collins (Exeter University, Exeter, United Kingdom)

14:30

ENSO and the Tropical Pacific in a Changing Climate

M. Mcphaden (NOAA/PMEL, Seattle, United States of America)

Abstract details
ENSO and the Tropical Pacific in a Changing Climate

M. Mcphaden (1)
(1) NOAA/PMEL, Seattle, United States of America

Abstract content

The El Niño/Southern Oscillation (ENSO) cycle represents the strongest year to year fluctuation of the climate system on the planet.  El Niño, the warm phase of ENSO, and La Niña, the cold phase of ENSO, arise through coupled ocean-atmosphere interactions in the tropical Pacific mediated by  positive feedbacks between surface wind and sea surface temperature variations.  Warm and cold ENSO episodes lead to global shifts in patterns of weather variability that cause droughts, floods, heat waves and other extreme events around the world.  ENSO-related natural disasters have significant consequences for society in terms of lives lost, property damage and economic vitality.  Understanding how ENSO may change in the future as a result of anthropogenic greenhouse gas forcing is therefore a compelling question that has challenged the scientific community. This presentation will review our current understanding of ENSO dynamics, predictability, and societal impacts. It will also assess current efforts to understand how ENSO may change in the future based on analyses of the instrumental record, CMIP models, and paleo data.

14:48

Indian Ocean interannual to decadal variability in the context of climate change

J. Vialard (IRD, Paris, France), W. Han (University of Colorado, Boulder, United States of America), M. Lengaigne (UPMC, Paris, France), A. Nidheesh, (National Institute of Oceanography, Goa, India), V. Parvathi, (National Institute of Oceanography, Goa, India), I. Suresh, (National Institute of Oceanography, Goa, India)

Abstract details
Indian Ocean interannual to decadal variability in the context of climate change

J. Vialard (1) ; W. Han (2) ; M. Lengaigne (3) ; A. Nidheesh, (4) ; V. Parvathi, (4) ; I. Suresh, (4)
(1) IRD, LOCEAN, Paris, France; (2) University of Colorado, Boulder, United States of America; (3) UPMC, Paris, France; (4) National Institute of Oceanography, Goa, India

Abstract content

In the sixties, the Indian Ocean was the focus of the oceanographer’s international community due to its dynamic response to monsoons. In the eighties, this focus shifted entirely to the neighbouring Pacific, berth of the El Niño Southern Oscillation (ENSO), most powerful interannual climate mode on earth. It is only at the turn of the century that the Indian Ocean came back into fashion with the discovery of its own intrinsic interannual climate variability (the Indian Ocean Dipole) and the development of a basin-wide observing network. After reviewing interannual variability of the Indian Ocean, I will turn to the natural decadal climate variability, which has comparatively been much less described in this basin than in the Pacific and Atlantic Oceans. I will in particular question if this decadal variability purely arises from the neighbouring Pacific or if an intrinsic variability also exists in the Indian Ocean. The climate change signal will finally be discussed in the Indian Ocean. We will show, on the particular example of anoxic events along the west coast of India, how long-term trends and shorter-term variability can cause extreme events with important societal consequences.

15:06

21st century projections for the Pacific region

S. Power (Bureau of Meteorology, Melbourne, Australia), M. Collins (Exeter University, Exeter, United Kingdom), K. Hennessy (SCIRO, Dickson, Australia), E. Guilyardi (LOCEAN/IPSL, Paris, France)

Abstract details
21st century projections for the Pacific region

S. Power (1) ; M. Collins (2) ; K. Hennessy (3) ; E. Guilyardi (4)
(1) Bureau of Meteorology, Cawcr, Melbourne, Australia; (2) Exeter University, Exeter, United Kingdom; (3) SCIRO, Dickson, Australia; (4) LOCEAN/IPSL, UPMC case 100, Paris, France

Abstract content

Here we will examine the latest scientific information available on projections for climate in the Pacific, and what this means for developing island states in the region. Particular attention will be paid to changes in surface temperature, winds, rainfall, El Nino, tropical cyclones, and ocean acidification, for different scenarios of future greenhouse gas emissions. The continuing importance of decadal climate variability for the region will also be highlighted. This presentation will draw upon the latest IPCC report and more recent research, including research conducted in the Pacific Australia Climate Change Science and Adaptation Planning Project.

15:24

Southern Ocean in a changing climate

A. Thompson (Caltech , Los Angeles, United States of America)

Abstract details
Southern Ocean in a changing climate

A. Thompson (1)
(1) Caltech , Los Angeles, United States of America

Abstract content

Recent Southern Ocean studies have suggested a slowdown of ocean carbon sequestration, an acidification of the water-masses, an overall warming and freshening in the vicinity of Antarctica, and drastic changes in sea-ice and ice-shelf distributions. Observed changes are profound: the warming rate is faster than the global average, and occurs in the deepest layers of the ocean, therefore isolating the climate signal for decades to millennia ; ice-shelves are melting, which accelerates the discharge of the ice sheet via the ice streams, and has a direct and major impact on the global sea level rise. These important changes are directly related to the large-scale circulation of the Southern Ocean and the associated biogeochemistry. This talk aims at summarizing our current understanding of how the large-scale circulation of the Southern Ocean works, how it impacts the carbon cycle, and how interactions with the Antarctic cryosphere influence it. 

15:42

Future changes in the South Pacific convergence zone and its tropical cyclones using regional dynamical downscaling

M. Lengaigne (UPMC, Paris, France), M. Bador (CERFACS, Toulouse, France, France), C. Menkes (IRD, Noumea, New Caledonia), J. Lefèvre (IRD, Noumea, New Caledonia), N. Jourdain (CNRS, grenoble, France), S. Jullien (UPMC, Paris, France), P. Marchesiello (IRD, Toulouse, France), S. Thibaut (CNRS, Toulouse, France), L. Terray (CERFACS/CNRS, Toulouse, France)

Abstract details
Future changes in the South Pacific convergence zone and its tropical cyclones using regional dynamical downscaling

M. Lengaigne (1) ; M. Bador (2) ; C. Menkes (3) ; J. Lefèvre (4) ; N. Jourdain (5) ; S. Jullien (6) ; P. Marchesiello (7) ; S. Thibaut (8) ; L. Terray (9)
(1) UPMC, Paris, France; (2) CERFACS, Climate Modelling and Global Change team, Toulouse, France, France; (3) IRD, LOCEAN, Noumea, New Caledonia; (4) IRD, Legos, Noumea, New Caledonia; (5) CNRS, Lgge, grenoble, France; (6) UPMC, Locean, Paris, France; (7) IRD, Legos, Toulouse, France; (8) CNRS, Legos, Toulouse, France; (9) CERFACS/CNRS, Sciences de l'Univers au CERFACS, URA1875, Toulouse, France

Abstract content

The South Pacific Convergence Zone (SPCZ) is the largest convective area of the Southern Hemisphere and has been recognized as a hot spot for climate variability (CLIVAR, 2012) as its functioning is poorly understood. Regionally, the SPCZ is the main source of rainfall in a vast majority of the Southern Pacific Island nations and the strong precipitation gradients related to the SPCZ make local hydrological conditions very sensitive to small displacement of this rain belt. The interannual variability of the SPCZ location is related to the El Niño/Southern Oscillation. El Niño events tend to occur accordingly with a northeastward displacement of the SPCZ, and La Niña events tend to occur with a southwestward displacement of the SPCZ. During strong El Niño events, the SPCZ undergoes an extreme swing by up to ten degrees of latitude toward the equator and collapses to a more zonally oriented structure. The SPCZ location not only strongly constrains the hydrological cycle but is also the breeding ground of tropical cyclones (TCs) in the South Pacific, as it combines all the large-scale atmospheric conditions that favor the genesis of TCs. Current climate models poorly reproduce the key characteristics of the SPCZ, leading to large uncertainties in the potential evolution of the South Pacific TC activity. Hence, assessing the SPCZ and its tropical cyclones in the future climate remains a challenge.

Here, we use a dynamical downscaling approach. Using results from an ensemble of 14 CMIP3 climate models under the SRES-A2 greenhouse gas scenario, we force a regional configuration of the WRF atmospheric model. The configuration uses a two-way nesting approach to increase the spatial resolution from 1° to 1/3° in the SPCZ region. We first perform a control simulation forced by the NCEP2 reanalysis over the past 30 years, and a future simulation based on an anomaly method (e.g. Zhao et al. 2009), where we add the mean 21st century regional SST warming pattern and atmospheric change along lateral boundaries to the NCEP2 fields.

Results show an accurate representation of the SPCZ location, its north-south displacements in response to El Niño/Southern Oscillation, as well as a correct TC distribution in the region. The future simulation indicates an increase of the precipitation within the SPCZ and the equatorial region, and a decrease northeast of the SPCZ mean location, in good agreement with climate models. The mean SPCZ location under future conditions presents a southward shift in its eastern part, and generally an increased variability of its interannual geographical position. We also find more frequent strong El Niño events in the future, with zonally oriented SPCZ. We explore the respective role of increased greenhouse gases in the domain versus the role of lateral boundaries. Large-scale conditions from lateral boundaries induce a significant (-20%) decrease of cyclones frequencies in the region. However, greenhouse gases locally counter this decrease. Overall, we do not find any significant change of cyclone frequencies in the Southwest Pacific in a warmer climate, in contrast with most recent studies, which find a decrease of cyclogenesis (-6% to -34% according to references gathered in Knutson et al. 2010).