Elsevier

Global and Planetary Change

Volumes 80–81, January 2012, Pages 149-164
Global and Planetary Change

Review Paper
Climate change impacts on tropical cyclones and extreme sea levels in the South Pacific — A regional assessment

https://doi.org/10.1016/j.gloplacha.2011.10.006Get rights and content

Abstract

This paper reviews the current understanding of the effect of climate change on extreme sea levels in the South Pacific region. This region contains many locations that are vulnerable to extreme sea levels in the current climate, and projections indicate that this vulnerability will increase in the future. The recent publication of authoritative statements on the relationship between global warming and global sea level rise, tropical cyclones and the El Niño-Southern Oscillation phenomenon has motivated this review. Confident predictions of global mean sea level rise are modified by regional differences in the steric (density-related) component of sea level rise and changing gravitational interactions between the ocean and the ice sheets which affect the regional distribution of the eustatic (mass-related) contribution to sea level rise. The most extreme sea levels in this region are generated by tropical cyclones. The intensity of the strongest tropical cyclones is likely to increase, but many climate models project a substantial decrease in tropical cyclone numbers in this region, which may lead to an overall decrease in the total number of intense tropical cyclones. This projection, however, needs to be better quantified using improved high-resolution climate model simulations of tropical cyclones. Future changes in ENSO may lead to large regional variations in tropical cyclone incidence and sea level rise, but these impacts are also not well constrained. While storm surges from tropical cyclones give the largest sea level extremes in the parts of this region where they occur, other more frequent high sea level events can arise from swell generated by distant storms. Changes in wave climate are projected for the tropical Pacific due to anthropogenically-forced changes in atmospheric circulation. Future changes in sea level extremes will be caused by a combination of changes in mean sea level, regional sea level trends, tropical cyclone incidence and wave climate. Recommendations are given for research to increase understanding of the response of these factors to climate change. Implications of the results for adaptation research are also discussed.

Introduction

There can be few locations in the world that are more vulnerable to the impacts of climate change than the low-lying atoll island nations of the Pacific (Fig. 1). Even at current mean sea levels, vulnerability to extreme sea levels is large. For instance, in 1972, Cyclone Bebe caused great damage to Funafuti, leaving behind a large rampart of coral debris (Maragos et al., 1973). In 1990, Cyclone Ofa struck Samoa, with a high storm tide inundating many low-lying coastal regions. In 1997, the storm surge from Cyclone Gavin breached sea walls on the north coast of Vanua Levu island in Fiji, causing extensive flooding of Labasa town, the largest urban area on the island. In 2004, large waves accompanying Cyclone Heta caused significant damage to Niue, with much of the infrastructure on the island destroyed (Terry, 2007). Other significant impacts have occurred, highlighting the vulnerability of this region to inundation from extreme sea levels.

Predicted rising sea levels will lead to increases in inundation that put the future viability of human habitation on a number of Pacific islands at risk (Mimura et al., 2007, Nicholls and Cazenave, 2010). Increases in extreme sea levels are arguably the most significant threat that this region faces from anthropogenic climate change (Mimura et al., 2007), yet our ability to predict the future vulnerability of this region is limited. The main reason is that the climate of the tropical Pacific is already extremely variable due to the strong influence of the El Niño Southern Oscillation (ENSO) phenomenon, which has its source in this region (Sarachik and Cane, 2010). This makes it difficult to detect any trends above the existing large interannual variability. In addition, predictions of future tropical cyclone incidence in this region generally indicate substantial decreases in numbers, but current interannual variability of cyclone incidence is also very large (e.g. Chand and Walsh, 2009).

The recent publication of authoritative review papers on the effects of climate change on ENSO (Collins et al., 2010), climate change on tropical cyclones (Knutson et al., 2010a) and sea level rise and variability (Church et al., 2010b) provides an opportunity to reassess the possible impacts of climate change on extreme sea levels in the South Pacific, since in the current climate the interannual variation of both tropical cyclone behaviour and extreme sea levels is dominated by ENSO.

Extreme sea levels are the result of several coinciding processes, including astronomical tides and severe weather events such as tropical cyclones, which generate elevated coastal sea levels through storm surge and high waves (Fig. 2). Storm surges from tropical cyclones are well-known and documented events along many tropical continental shelf regions, where destructive sea levels are caused by the inverse barometer effect (IBE) and wind stress over the shelf seas (e.g. Fritz et al., 2007, Dube et al., 2009, Harper et al., 2009). Sea levels along the open coast may be further elevated by wave breaking processes. Paradoxically, the shelf conditions that favour high storm surges tend to attenuate the contribution of waves, and the shelf conditions that act to attenuate storm surges allow a larger contribution of waves. This is because wide and gently sloping continental shelves cause waves to steepen, break and lose energy and height further offshore, thereby reducing the wave heights at the coast. Steep shelf margins such as those that surround many islands and atolls in the Pacific, on the other hand, are less conducive to high storm surges but may instead support larger wave-induced contributions to sea level anomalies, which have been reported at Midway Atoll in the northern tropical Pacific by Hoeke (2010).

Tropical cyclone-induced storm surges tend to be localised and concentrated in the region of maximum onshore winds close to the cyclone centre. While potentially devastating, they are rare at any given location and therefore contribute to the extreme tails of the distribution of sea level anomalies. The waves generated by such systems, on the other hand, can propagate for thousands of kilometres in the deep ocean as swell with little loss of energy, potentially affecting a larger number of more distant shorelines. Therefore they may contribute to more frequent sea level anomalies, although these may be of smaller magnitude than the combined impacts of storm surge and local storm waves. Tidal extremes vary on predictable time scales due to the relative movement of the Earth, Sun and Moon. These short term increases in sea level may occur on a background of longer term changes brought about by modes of variability such as ENSO and climate change. While tectonic disturbances may generate tsunamis that may also cause extreme coastal sea levels, they are not addressed in this review as they are not climate-related.

The effect of anthropogenic climate change on mean sea levels, tropical cyclone and ENSO behaviour provides several avenues by which extreme sea levels may also be affected in the future. Rising sea levels due to thermal expansion of the warming oceans and the melting of glaciers, ice caps and the large ice sheets of Antarctica and Greenland will increase the background sea levels on which extreme events occur. Climate change may also cause changes to the behaviour of tropical cyclones by modifying their frequency, intensity and preferred regions of occurrence (Sugi et al., 2009, Bender et al., 2010, Lavender and Walsh, 2011). It may also affect modes of climate variability such as ENSO which in turn may influence background sea levels (e.g. Church et al., 2006, Lowe et al., 2010) and cyclone behaviour (e.g. Knutson et al., 2010a). Finally, the relative contribution of local storm surge and wave forcing, along with remotely generated swell, to positive sea level anomalies at a given location will determine how climate-driven changes to meteorological forcing will affect future changes to sea level extremes. The interactions between climate change and the various drivers of sea level anomalies are illustrated in Fig. 3.

The future vulnerability of tropical and subtropical islands in this region to extreme sea levels is therefore the topic of this review, whose purpose is to provide the most up-to-date quantitative estimates of future impacts over the Pacific Climate Change Science Program (PCCSP)1 region delineated in Fig. 1. A summary of vulnerability for the near-equatorial islands of the North Pacific is thus also included, due to their proximity to the centre of action of ENSO, the main influence on climate in the South Pacific. In Section 2 of this paper, we give an overview of global trends and projections in meteorological and oceanographic conditions that influence the incidence of extreme sea levels in the PCCSP region. Section 3 contains a summary of these observed trends in the PCCSP region and Section 4 details projections of future trends. Section 5 gives an analysis of the reasons for the projected trends, along with a summary of the reasons for remaining uncertainties, while Section 6 provides concluding remarks.

Section snippets

ENSO

There are numerous summaries of the effects of global climate and climate variability on the tropical Pacific (Rasmusson and Carpenter, 1982, Philander, 1990, Larkin and Harrison, 2001, Sarachik and Cane, 2010). This paper will not repeat this work but will focus on the main global drivers of variability in tropical cyclone incidence and extreme sea levels in the PCCSP region.

ENSO is the most important global mode of climate variability, with influences worldwide but with strongest effects in

ENSO

There were substantial trends in surface pressures and associated changes in circulation in the Pacific during the last century. Fig. 4 shows trends in sea level pressures over the equatorial Pacific and Indian oceans from 1871 to 1992. There has been a clear change in the mean state during this time, with pressures rising over the Maritime Continent2 and northern Australia and falling over much of the tropical

ENSO

Collins et al. (2010) review our current understanding of projected global trends in ENSO. As they note, observed changes in east–west Pacific tropical pressure gradients are clear (Fig. 4) and are consistent with a weakening of the Hadley and associated Walker circulations (Vecchi and Soden, 2007). This weakening is projected to continue into the future but is not likely to be associated with SST anomaly patterns that are similar to present-day El Niño anomaly fields. This concept is important

Analysis of the problem

In the previous section, it was shown that almost all models predicted a decrease in tropical cyclone numbers in a warmer world in the South Pacific region. This is also true globally. At least two main hypotheses have been proposed to explain this result. The first is that while an increase in SST is usually associated with an increase in PI, the tropical atmosphere is usually more stable in a warmer world than in the current climate, thus making it more difficult for tropical cyclones to

Research recommendations and implications for adaptation

As discussed in this paper, future changes to sea level extremes in the Pacific due to anthropogenic global warming will be affected by changes to tropical cyclones, and by future differences in climate variability, including the El Nino Southern Oscillation phenomenon. Sea level extremes will also be affected by wave climate change and rising sea levels. There remain significant barriers to reducing the uncertainties associated with future projections of these factors. These uncertainties have

Acknowledgements

The authors would like to thank the Pacific Climate Change Science Program of the Australian Department of Climate Change and Energy Efficiency for partially funding this research. The authors would also like to thank their respective institutions for supporting this work. They are grateful to Dr Neil White for valuable discussions and for providing Fig. 7.

References (129)

  • W.M. Briggs

    On the changes in the number and intensity of North Atlantic tropical cyclones

    Journal of Climate

    (2008)
  • S. Caires et al.

    A new non-parametric method to correct model data: application to significant wave height from the ERA-40 reanalysis

    Journal of Atmospheric and Oceanic Technology

    (2005)
  • J. Callaghan et al.

    Variability and decline in the number of severe tropical cyclones making land-fall over eastern Australia since the late nineteenth century

    Climate Dynamics

    (2010)
  • S.J. Camargo et al.

    Western North Pacific tropical cyclone intensity and ENSO

    Journal of Climate

    (2005)
  • A. Cazenave et al.

    Contemporary sea level

    Annual Review Marine Science

    (2010)
  • J.C.L. Chan

    Decadal variations of intense typhoon occurrence in the western North Pacific

    Proceedings of the Royal Society of London Series A

    (2007)
  • S.S. Chand et al.

    Tropical cyclone activity in the Fiji region: spatial patterns and relationship to large-scale circulation

    Journal of Climate

    (2009)
  • S.S. Chen et al.

    The CBLAST-Hurricane program and the next-generation fully coupled atmosphere–wave–ocean models for hurricane research and prediction

    Bulletin of the American Meteorological Society

    (2007)
  • M.R. Chowdhury et al.

    ENSO and seasonal sea-level variability — a diagnostic discussion for the U.S.-Affiliated Pacific Islands

    Theoretical and Applied Climatology

    (2007)
  • M.R. Chowdhury et al.

    Sea level extremes in the U.S.-Affiliated Pacific Islands — a coastal hazard scenario to aid in decision analyses

    Journal of Coast Conservation

    (2010)
  • J.A. Church et al.

    Ocean temperature and salinity contributions to global and regional sea-level change

  • J.A. Church et al.

    Understanding and projecting sea level change

    Oceanography

    (2011)
  • J.A. Church et al.

    Sea-level rise from the late 19th to the early 21st century

    Surveys in Geophysics

    (2011)
  • J.A. Church et al.

    Understanding Sea Level Rise and Vulnerability

    (2010)
  • K.M. Cobb et al.

    El Niño/southern oscillation and tropical Pacific climate during the last millennium

    Nature

    (2003)
  • M. Collins et al.

    The impact of global warming on the tropical Pacific Ocean and El Niño

    Nature Geoscience

    (2010)
  • C. Deser et al.

    Twentieth century tropical sea surface temperature trends revisited

    Geophysical Research Letters

    (2010)
  • C. Deser et al.

    Sea surface temperature variability: patterns and mechanics

    Annual Review of Marine Science

    (2010)
  • S. Dessai et al.

    Climate prediction: a limit to adaptation?

  • S.K. Dube et al.

    Storm surge modelling for the Bay of Bengal and Arabian Sea

    Naturals Hazards

    (2009)
  • J.B. Elsner et al.

    The increasing intensity of the strongest tropical cyclones

    Nature

    (2008)
  • K.A. Emanuel

    The dependence of hurricane intensity on climate

    Nature

    (1987)
  • K.A. Emanuel

    Increasing destructiveness of tropical cyclones over the past 30 years

    Nature

    (2005)
  • K. Emanuel et al.

    Hurricanes and global warming: results from downscaling IPCC AR4 simulations

    Bulletin of the American Meteorological Society

    (2008)
  • C.K. Folland et al.

    Trends and variations in South Pacific island and ocean surface temperatures

    Journal of Climate

    (2003)
  • S.B. Goldenberg et al.

    The recent increase in Atlantic hurricane activity: causes and implications

    Science

    (2001)
  • N. Gomez et al.

    A new projection of sea level change in response to collapse of marine sectors of the Antarctic Ice Sheet

    Geophysical Journal International

    (2010)
  • Government of Niue

    National impact assessment of cyclone Heta

    Economic Planning, Development and Statistics

    (2004)
  • A. Grinsted et al.

    Reconstructing sea level from paleo and projected temperatures 200 to 2100 AD

    Climate Dynamics

    (2009)
  • S. Gualdi et al.

    Changes in tropical cyclone activity due to global warming: results from a high-resolution coupled general circulation model

    Journal of Climate

    (2008)
  • E. Guilyardi et al.

    Understanding El Niño in ocean–atmosphere general circulation models: progress and challenges

    Bulletin of the American Meteorological Society

    (2009)
  • S.K. Gulev et al.

    Last century changes in ocean wind wave height from global visual wave data

    Geophysical Research Letters

    (2004)
  • B. Harper et al.

    Developments in storm tide modelling and risk assessment in the Australian region

    Natural Hazards

    (2009)
  • I.M. Held et al.

    Robust responses of the hydrological cycle to global warming

    Journal of Climate

    (2006)
  • M.A. Hemer

    Historical trends in Southern Ocean storminess: long‐term variability of extreme wave heights at Cape Sorell, Tasmania

    Geophysical Research Letters

    (2010)
  • M.A. Hemer et al.

    Variability and trends in the directional wave climate of the Southern Hemisphere

    International Journal of Climatology

    (2010)
  • M.A. Hemer et al.

    Coordinated global ocean wave projections

    Bulletin of the American Meteorological Society

    (2010)
  • Hoeke, R., 2010. Wave driven sea level anomaly at Midway Atoll. Ph.D. thesis, James Cook University, 102...
  • G.J. Holland

    On the quality of the Australian tropical cyclone data base

    Australian Meteorological Magazine

    (1981)
  • G.J. Holland

    The maximum potential intensity of tropical cyclones

    Journal of Atmospheric Science

    (1997)
  • Cited by (118)

    • A locally relevant framework for assessing the risk of sea level rise under changing temperature conditions: Application in New Caledonia, Pacific Ocean

      2022, Science of the Total Environment
      Citation Excerpt :

      However, lack of reliable data and operational resources prevent the application of these models in some of the most vulnerable parts of the globe (see e.g. Kelman and West, 2009; Martin et al., 2015; Faivre et al., 2021). Changes in the sea level can be also estimated using data-driven models that are forced by downscaled climate projections (Rahmstorf, 2010; Bittermann et al., 2013; Leta et al., 2018) as well as astronomical tides (Walsh et al., 2012; Salvadori et al., 2016), and/or storm surges (Khanal et al., 2019). These models are particularly suitable for impact assessment at the local scale and can range from simple trend models (Chatfield, 2000; Hess et al., 2001; Kozłowski et al., 2018) to complicated statistical and machine learning models (Vermeer and Rahmstorf, 2009; Niedzielski and Kosek, 2009; Imani et al., 2014, 2021; Ardabili et al., 2019).

    View all citing articles on Scopus
    View full text