Two Centuries of Climate Change and Climate Variability, East Coast Australia
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Journal of Marine Science and Engineering Article Two Centuries of Climate Change and Climate Variability, East Coast Australia Peter Helman and Rodger Tomlinson * ID Griffith Centre for Coastal Management, Griffith University, Gold Coast 4222, Australia; [email protected] * Correspondence: r.tomlinson@griffith.edu.au; Tel.: +61-7-5552-8499 Received: 11 December 2017; Accepted: 19 December 2017; Published: 3 January 2018 Abstract: On the east Australian coast, climate change is expressed as a slowly rising sea level. Analysis of records, dating back over two centuries, also shows oscillating multidecadal ‘storm’ and ‘drought’ dominated climate periods that are distinct from long-term climate change. Climate variability, as expressed by these distinct multidecadal periods, is generally associated with phases of the Interdecadal Pacific Oscillation Index (IPO). Two centuries of climate and coastline response are examined for the central east coast of Australia, between Fraser Island and Coffs Harbour. The long record has been compiled by analysing a wide range of indicators and observations, including: historical accounts, storm records, sea level trends, assessment of storm erosion faces, and coastal movement in relation to fixed monuments, surveys, and maps. Periods of suppressed sea level, beach accretion, and drought were found to be associated with strongly positive IPO. Periods of higher sea level, increased storminess, and beach erosion were associated with strongly negative IPO. Understanding the behaviour of climate variability over different timescales has the potential to improve the understanding of, and responses to, climate change. This will be important in the sustainable management of geomorphic and ecological systems. Keywords: IPO; climate change; climate variability; sea level rise; coastal erosion; Australia 1. Introduction Climatic and geomorphic evidence indicates that the east Australian coastline observed by the first Europeans settlers 200 years ago was experiencing a relatively stable climatic period, when the sea level was slightly below that in the present. Consistent findings of slowly receding shorelines and erosion of Holocene dunes suggest that the coast was influenced by slowly rising sea levels from the early 1800s to present day [1]. Simulation from HadCM3 [2] shows a trend of global sea level rise from 1820. The east coast sea level rise follows, but has been below the global mean, due to the non-uniform distribution of thermal expansion resulting in different regional rates of sea level rise [3]. Pacific Ocean sea surface temperature (SST) has been recorded in ships’ logs from the mid-1800s and has been modelled to show an Interdecadal Pacific Oscillation (IPO). The IPO index oscillates irregularly as positive and negative phases over several decades, resulting in major climate shifts [4–7]. References [8,9] relate oceanic ecosystem production and salmon catches in the North Pacific Ocean to decadal phases of IPO. The authors of Reference [10] observed that sea level at Auckland rises at a slower rate during positive IPO phases than in negative phases. IPO interacts with, and modifies, the inter-annual variation described by El Niño-Southern Oscillation (ENSO). The Southern Oscillation Index (SOI) gives an indication of the development and intensity of El Niño or La Niña events in the Pacific Ocean and is calculated using the pressure differences between Tahiti and Darwin. The variability in SOI is largely due to the influence of the widely understood and discussed two- to seven-year ENSO cycles. Inter-annual variation of the annual mean sea level from Sydney shows a far greater magnitude of change than long-term trends (over 100 years). The IPO also appears to modulate the frequency J. Mar. Sci. Eng. 2018, 6, 3; doi:10.3390/jmse6010003 www.mdpi.com/journal/jmse J. Mar. Sci. Eng. 2018, 6, 3 2 of 8 Inter-annual variation of the annual mean sea level from Sydney shows a far greater magnitude of change than long-term trends (over 100 years). The IPO also appears to modulate the frequency of El Niño events, whereby the occurrence of El Niño events is shown to be significantly elevated during the positive phase, with the last 350 years showing that the frequency of La Niña is significantly higher during negative IPO phases [6]. Reference [11] reported that for recent decades J. Mar. Sci. Eng. 2018, 6, 3 2 of 8 (1979–2015), coastal vulnerability across the Pacific correlates with ENSO. The combination of IPO and ENSO provides the broad framework for understanding Australian climate episodic behaviour. of El Niño events, whereby the occurrence of El Niño events is shown to be significantly elevated 2. Methodsduring the positive phase, with the last 350 years showing that the frequency of La Niña is significantly higher during negative IPO phases [6]. Reference [11] reported that for recent decades (1979–2015), Projectingcoastal vulnerability trends fromacross studies the Pacific such correlatesas Referenc withe [11], ENSO. which The analyse combination data of from IPO periods and ENSO of years to decades,provides is the questioned. broad framework Analysis for understanding over decadal Australian or centennial climate episodic scales behaviour.provides a method for separating the influence of climate change from climatic variation in coastal dynamics. Two 2. Methods centuries of climate and coastline response are examined for the central east coast of Australia, between FraserProjecting Island trends and from Coffs studies Harbour. such as ReferenceThe long [11record], which has analyse been datacompiled from periods by analysing of years toa wide range decades,of indicators is questioned. and observations, Analysis over including decadal or historical centennial accounts, scales provides storm a methodrecords, for sea separating level trends, the influence of climate change from climatic variation in coastal dynamics. Two centuries of climate assessment of storm erosion faces, coastal movement in relation to fixed monuments, surveys, and and coastline response are examined for the central east coast of Australia, between Fraser Island maps [1]. and Coffs Harbour. The long record has been compiled by analysing a wide range of indicators and Toobservations, identify underlying including historical climate accounts, change stormtrends, records, recorded sea level changes trends, to assessment the coastline of storm were erosion compared to estimatesfaces, coastal of sea movement level, observed in relation records to fixed of monuments, annual mean surveys, sea level, and maps and [ 1projected]. sea level trends. Climate variabilityTo identify was underlying analysed climate by identifying change trends, storm, recorded drought, changes and to flood the coastline events were on the compared coast. to estimates of sea level, observed records of annual mean sea level, and projected sea level trends. 3. FindingsClimate variability was analysed by identifying storm, drought, and flood events on the coast. 3. Findings 3.1. Sea Level and Climate Change 3.1. Sea Level and Climate Change On the east coast of Australia, a slowly rising sea level (Figure 1) has resulted in permanent coastal changes:On the eastbreaching coast of of Australia, coastal adunes, slowly barrier rising sea island level formation, (Figure1) has loss resulted of spits, in permanent and growth of flood coastaltide deltas changes: [1,12–14]. breaching The of co coastalastline dunes, has been barrier moving island inland formation, throughout loss of spits, the andlast growthtwo centuries, of largelyflood unperceived tide deltas as [1, 12the–14 rate]. The of coastlinesea level has rise been has movingbeen low inland and throughout movement the well last within two centuries, the range of largely unperceived as the rate of sea level rise has been low and movement well within the range of climatic variability. Little concern has been raised as most of the eroded land is public reserve which climatic variability. Little concern has been raised as most of the eroded land is public reserve which has actedhas actedas an as effect an effectiveive coastline coastline buffer. buffer. FigureFigure 1. Trend 1. Trend of sea of sealevel level rise, rise, east east coast coast Australia, Australia, 1830–2080.1830–2080. Estimated Estimated from from 1840 1840 [15]; [15]; observed observed (Sydney(Sydney Permanent Permanent Service Service for for MeanMean Sea Sea Level Level (PSMSL) (PSMSL) data), projections—Intergovernmentaldata), projections—Intergovernmental Panel Panel onon ClimateClimate Change Change (IPCC) (IPCC) 2007. 2007. 3.2. IPO3.2. and IPO Sea and Level Sea Level Quarterly IPO indices from the Hadley Centre, UK1 were converted to annual means from 1871 Quarterly IPO indices from the Hadley Centre, UK1 were converted to annual means from 1871 and compared to detrended Sydney annual mean sea level (Figure2). When IPO is plotted inversely, and compared to detrended Sydney annual mean sea level (Figure 2). When IPO is plotted inversely, 1 1 IPO (plotted inverse) 1856 to 1870 after Reference [4]. 1871–2013 version HADISST IPO JFM1871-AMJ2004, low pass IPO (plotted11-year Chebyshevinverse) 1856 filtered to from 1870 Hadley after Centre, Reference Meteorology [4]. Office,1871–2013 UK. Dataset version supplied HADISST by Scott Power, IPO JFM1871-AMJ2004, Research Centre, low passBureau 11-year of Meteorology, Chebyshev Melbourne. filtered from Hadley Centre, Meteorology Office, UK. Dataset supplied by Scott Power, Research Centre, Bureau of Meteorology, Melbourne.