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This study presents the first assessment of the observed frequency of the impacts of high sea levels at locations along Australia’s northern coastline. We used a new methodology to systematically define impact-based thresholds for coastal tide gauges, utilising reports of coastal inundation from diverse sources. This method permitted a holistic consideration of impact-producing relative sea-level extremes without attributing physical causes. Impact-based thresholds may also provide a basis for the development of meaningful coastal flood warnings, forecasts and monitoring in the future. These services will become increasingly important as sea-level rise continues.The frequency of high sea-level events leading to coastal flooding increased at all 21 locations where impact-based thresholds were defined. Although we did not undertake a formal attribution, this increase was consistent with the well-documented rise in global sea levels. Notably, tide gauges from the south coast of Queensland showed that frequent coastal inundation was already occurring. At Brisbane and the Sunshine Coast, impact-based thresholds were being exceeded on average 21.6 and 24.3 h per year respectively. In the case of Brisbane, the number of hours of inundation annually has increased fourfold since 1977.

As global mean sea level continues to rise, thresholds corresponding to coastal inundation impacts are exceeded more frequently. This paper aims to relate sea level rise (SLR) observations and projections to their physical on‐the‐ground impacts. Using a large coastal city as an example, we show that in Sydney, Australia, frequencies of minor coastal inundation have increased from 1.6 to 7.8 days per year between 1914 and present day. We attribute over 80% of the observed coastal inundation events between 1970 and 2015 to the predominantly anthropogenic increases in global mean sea level. Further, we find that impact‐producing coastal inundation will occur weekly by 2050 under high‐ and medium‐emission/SLR scenarios and daily by 2100 under high emissions. The proportion of tide‐only coastal inundation events (i.e., where no storm surge is required to exceed flood thresholds) will increase with SLR, such that most coastal inundation events, including those considered historically severe, will become a predictable consequence of SLR and astronomical tides. These findings are important for coastal managers as frequency, severity, and predictability of inundation impacts can all now be related to the amount of SLR (e.g., a planning allowance or SLR projection). By incorporating known historical inundation events, this allows contextualization, visualization, and localization of global SLR and the changing nature of future coastal inundation risk.

El Nino-Southern Oscillation (ENSO) plays a dominant role in interannual climate variability in Pacific island countries, directly affecting lives there. Many countries show different rainfall responses depending on the sea surface temperature (SST) structure of different types of El Nino events. El Nino events are classified into three types based on previous studies: those with strongest SST anomalies in the eastern Pacific Cold Tongue region (CTE), in the Western Pacific Warm Pool region (WPE), and those in between, a “Mixed” El Nino (MxE), and results from 30 CMIP5 models are investigated. These models accurately reproduce observed SST and precipitation anomalies for the three El Nino types and La Nina. CMIP5 models simulate much larger ranges in the strength of ENSO events than observed. Results clarify the roles of both the different structures of El Nino SST anomalies and their magnitudes on rainfall in the Pacific, and demonstrate that each of the three El Nino types has different impacts on rainfall in the region. These impacts vary with location, with WPE and CTE producing very different impacts in most Pacific island countries. There is a linear intensification of both the mean and maximum rainfall anomalies in the equatorial Pacific as the events become stronger. Equatorial rainfall shifts eastward in CTE and MxE, westward in La Nina. Both the South Pacific and Intertropical Convergence Zones (SPCZ and ITCZ) shift equatorward in El Nino and poleward in La Nina, the shifts increasing as events strengthen. WPE show different behaviour to other events, with little east-west shift in equatorial rainfall, and the orientation angle of the convergence zones increases. Identification of models with no erroneous westward bias in SST anomalies has clarified the effect of strong CTE events producing “zonal” SPCZ and shifting rainfall away to the east from western equatorial countries.

Intermittent disruptions to rainfall patterns and intensity over the Pacific Ocean lasting up to ∼ 1 year 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., Intermittent rainfall changes over the Pacific Ocean can profoundly disrupt lives and ecosystems in many locations. Here, the authors show that the risk of such changes has increased, and that the risk could – even with a reduction in greenhouse gas emissions - remain elevated for decades to come.

El Niño–Southern Oscillation (ENSO) drives interannual climate variability in many tropical Pacific island countries, but different El Niño events might be expected to produce varying rainfall impacts. To investigate these possible variations, El Niño events were divided into three categories based on where the largest September–February sea surface temperature (SST) anomalies occur: warm pool El Niño (WPE), cold tongue El Niño (CTE), and mixed El Niño (ME), between the other two. Large-scale SST and wind patterns for each type of El Niño show distinct and significant differences, as well as shifts in rainfall patterns in the main convergence zones. As a result, November to April rainfall in many Pacific island countries is significantly different among the El Niño types. In western equatorial Pacific islands, CTE events are associated with drier than normal conditions whereas ME and WPE events are associated with significantly wetter than normal conditions. This is due to the South Pacific convergence zone and intertropical convergence zone moving equatorward and merging in CTE events. Rainfall in the convergence zones is enhanced during ME and WPE and the displacement is smaller. La Niña events also show robust impacts that most closely mirror those of ME events. In the northwest and southwest Pacific strong CTE events have much larger impacts on rainfall than ME and WPE, as SST anomalies and correspondingly large-scale surface wind and rainfall changes are largest in CTE. While variations in rainfall exist between different types of El Niño and the significant impacts on Pacific countries of each event are different, the two extreme CTE events have produced the most atypical impacts.

A set of 27 global climate models from the Coupled Model Inter-comparison Project Phase 5 (CMIP5) ensemble are assessed for their performance for the purpose of making future climate projection studies in the western tropical Pacific and differences to Coupled Model Inter-comparison Project Phase 3 (CMIP3) are assessed. The CMIP5 models show some improvements upon CMIP3 in the simulation of the climate in the western tropical Pacific in the late 20th century. There are fewer CMIP5 models with very poor skill scores than in CMIP3 for some measures and a small group of the well-performing models in CMIP5 have lower biases than in an equivalent group from CMIP3. These best-performing models could be particularly informative for studying certain climate sensitivities and feedbacks in the region. There is evidence to reject one model as unsuitable for making regional climate projections in the region, and another two models unsuitable for analysis of the South Pacific Convergence Zone (SPCZ). However, while there have been improvements, many of the systematic model biases in the mean climate in CMIP3 are also present in the CMIP5 models. They are primarily related to the shape of the transition between the Indo-Pacific warm pool and equatorial cold tongue, and the associated biases in the position and orientation of the SPCZ and Inter-Tropical Convergence Zone, as well as in the spatial pattern, variability and teleconnections of the West Pacific monsoon, and the simulation of El Nino Southern Oscillation. Overall, the results show that careful interpretation and consideration of biases is required when using CMIP5 outputs for generating regional climate projections for the western tropical Pacific, particularly at the country scale, just as there was with CMIP3.

Coupled General Circulation Models simulate broad-scale climate patterns and are standard tools for understanding potential changes to the climate system. Climate change projection information is required at the local scale for adaptation planning. Model skill can be limited at this scale due to model biases and uncertainties. Pacific Islands are one such example, particularly Nauru which lies at the intersection of the South Pacific Convergence Zone (SPCZ), the Western Pacific Monsoon, the oceanic warm pool and the ENSO zone of influence. In light of such constraints, a qualitative climate projection approach is presented whereby projections are based on expected changes to the broad-scale climate features, drawing on a review of current literature and new research. Nauru sits in the region subject to seasonal and interannual migrations of the SPCZ. Climate models simulate an overly zonal SPCZ with Nauru lying too close to the dry cold tongue zone. This sets an erroneous base state for Nauru by locating it in a very different climate zone. The climate model changes in the SPCZ can be used to argue how the climate of Nauru would change were it and the SPCZ correctly collocated. Similar approaches are applied to the set of climate features influencing Nauru to generate modified climate projections.

While the practice of reporting multi-model ensemble climate projections is well established, there is much debate regarding the most appropriate methods of evaluating model performance, for the purpose of eliminating and/or weighting models based on skill. The CMIP3 model evaluation undertaken by the Pacific Climate Change Science Program (PCCSP) is pre- sented here. This includes a quantitative assessment of the ability of the models to simulate 3 cli- mate variables: (1) surface air temperature, (2) precipitation and (3) surface wind); 3 climate fea- tures: (4) the South Pacific Convergence Zone, (5) the Intertropical Convergence Zone and (6) the West Pacific Monsoon; as well as (7) the El Nino Southern Oscillation, (8) spurious model drift and (9) the long term warming signal. For each of 1 to 9, it is difficult to identify a clearly superior sub- set of models, but it is generally possible to isolate particularly poor performing models. Based on this analysis, we recommend that the following models be eliminated from the multi-model ensemble, for the purposes of calculating PCCSP climate projections: INM-CM3.0, PCM and GISS-EH (consistently poor performance on 1 to 9); INGV-SXG (strong model drift); GISS-AOM and GISS-ER (poor ENSO simulation, which was considered a critical aspect of the tropical Pacific climate). Since there are relatively few studies in the peer reviewed literature that have attempted to combine metrics of model performance pertaining to such a wide variety of climate processes and phenomena, we propose that the approach of the PCCSP could be adapted to any region and set of climate model simulations.

Understanding how the South Pacific convergence zone (SPCZ) may change in the future requires the use of global coupled atmosphere–ocean models. It is therefore important to evaluate the ability of such models to realistically simulate the SPCZ. The simulation of the SPCZ in 24 coupled model simulations of the twentieth century is examined. The models and simulations are those used for the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC). The seasonal climatology and interannual variability of the SPCZ is evaluated using observed and model precipitation. Twenty models simulate a distinct SPCZ, while four models merge intertropical convergence zone and SPCZ precipitation. The majority of models simulate an SPCZ with an overly zonal orientation, rather than extending in a diagonal band into the southeast Pacific as observed. Two-thirds of models capture the observed meridional displacement of the SPCZ during El Niño and La Niña events. The four models that use ocean heat flux adjustments simulate a better tropical SPCZ pattern because of a better representation of the Pacific sea surface temperature pattern and absence of cold sea surface temperature biases on the equator. However, the flux-adjusted models do not show greater skill in simulating the interannual variability of the SPCZ. While a small subset of models does not adequately reproduce the climatology or variability of the SPCZ, the majority of models are able to capture the main features of SPCZ climatology and variability, and they can therefore be used with some confidence for future climate projections.

This paper presents a study of variability of climate indices and rainfall in southeast Queensland (SE Qld). Using high-resolution gridded rainfall data for all of Australia and global sea surface temperatures (SST), the relationship between rainfall Australia-wide and in SE Qld in particular with SST indices and the Southern Oscillation Index (SOI) have been investigated. It is found that SE Qld is more subject to the breakdown of correlations between the SOI and rainfall than any other part of Australia. Model predictions suggest that this is probable in the future. Considering only timescales longer than interannual, it was found that SSTs in the central tropical Pacific Ocean (TPO) (represented by the Nino-4 index) correlated best with SE Qld rainfall. Eastern TPO (Nino-3) SSTs and the SOI produced successively weaker correlations. The time series of the second modes of variability of SSTs over the Pacific and Indian Oceans were shown to have limited impact on SE Qld rainfall variability. The data was split into periods before and after 1946, when Australian mean rainfall changed (Pittock, 1975). While the SOI correlations with rainfall in SE Australia were similar in both periods, in SE Qld the correlations were very weak in the earlier period (0.06) but very strong in the latter (0.72). The Nino-4 index correlated better than the Nino-3 index in both periods, but they showed smaller changes from the earlier to the latter periods than the SOI.

The coastal region of the Antarctic continent is renowned for the frequent, intense blizzards and associated extreme weather that affect it, creating treacherous conditions that place human activities there in often perilous situations. The understanding and prediction of these events are therefore vital for continued safe operations on the continent. Severe wind events are investigated at two Australian coastal sites, Casey and Mawson. A summer case study at Casey and then the climatology of the events at the two stations are studied using station observations and atmospheric analyses. All events are found to be associated with extratropical cyclones that move close to the stations and lead to strong winds and heavy cloud cover. Most events see the passage of a high pressure ridge over the station ahead of the cyclone that blocks the cyclone, forcing it to move farther south close to the coast, thus intensifying the effect of the cyclone on the coastal weather. The ridge also produces calm, clea...

Extratropical cyclones of the southern hemisphere provide the primary mechanism of poleward horizontal heat and moisture transport. Their behaviour is influenced by the strength of the meridional temperature gradient in the mid troposphere. As the semi-annual oscillation (SAO) in the annual cycle of this gradient has become less dominant in recent years, we investigate the impact of modifying the gradient in two simulations with the Arpege general-circulation model. Model temperatures at 50°S near the 500 hPa level are increased (strengthening the gradient) or decreased (weakening the gradient) in two different simulations T50+ and T50−, respectively. The temperature nudging had a greater impact on the temperature gradient in T50+, but both simulations showed significant surface warming on the Antarctic coast in winter. In T50+, 500 hPa temperature and surface pressure gradients had weaker SAOs, as the circumpolar trough contracted and intensified and cyclone numbers increased along the Antarctic coast. The SAOs strengthened in T50−, and the trough became more disperse, but cyclone numbers increased north of 50°S. Baroclinicity increased (decreased) with a stronger (weaker) meridional temperature gradient, but the static stability of the atmosphere also changed with the opposite impact on baroclinicity. Thus, in T50+ the increase in cyclone numbers was greatest near the Antarctic coast but this was counteracted somewhat by the static stability increase north of 60°S. In T50− cyclone numbers increased north of 50°S because baroclinicity was increased by a stronger meridional temperature gradient and reduced static stability. Hence, the effect on the Antarctic surface climate was nonlinear, with a warmer coast in both cases in winter, and a windier East Antarctica in T50+ but calmer katabatic flow in T50−. Copyright © 2002 Royal Meteorological Society

Strong wind events occurring near Casey (Antarctica) in a long July GCM simulation have been studied to determine the relative roles played by the synoptic situation and the katabatic flow in producing these episodes. It has been found that the events are associated with strong katabatic and strong gradient flow operating together. Both components are found to increase threefold on average for these strong winds, and although the geostrophic flow is the stronger, it rarely produces strong winds without katabatic flow becoming stronger than it is in the mean. The two wind components do not flow in the same direction; indeed, there is some cancellation between them, since katabatic flow acts in a predominant downslope direction, while the geostrophic wind acts across slope. The stronger geostrophic flow is associated with higher-than-average pressures over the continent and the approach of a strong cyclonic system toward the mast and a blocking system downstream. The anomalous synoptic patterns lea...

[1] Atmospheric climate models now present powerful tools for studying atmospheric parameters relevant to the mass balance of the Greenland ice sheet, a significant uncertainty in global sea level. This study evaluates the simulations of the UK Hadley Centre atmospheric model (HadAM3) against observational data and reanalyses. HadAM3 reproduces the main precipitation patterns, but a positive bias exists in autumn over southern Greenland. The modeled North Atlantic storm track is well placed, but it and the polar vortex and hemispheric-scale wave activity are weaker than observed, which may impact on moisture flux over Greenland. Surface temperatures are 2°–3°C too warm in summer and up to 5°C too cold in winter, probably owing to the snow albedo varying too little throughout the year, and excess summer downward short-wave radiation flux and winter long-wave loss, related to insufficient cloud cover. The summer warm bias and the too coarsely represented ice sheet area lead to Greenland-mean melting being overestimated, and a negative surface mass balance is simulated. A higher-resolution ice sheet mask improves these quantities significantly. Increasing resolution is expected to remove most errors when orography and the ice sheet, particularly around the coastal margins where gradients are large, are better defined, as orographic dynamical deficiencies are minimized. A high-resolution version of the model is seen to improve the simulation of precipitation. Minor ice and snow physics improvements are needed, but the large-scale simulation produces good-quality inputs with no major bias for higher resolution limited area or downscaling models.