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Extreme temperature and precipitation events occurring in Australia in recent decades have caused significant socio-economic and environmental impacts, and thus determining the factors contributing to these extremes is an active area of research. Many recently occurring record-breaking temperature and rainfall events have now been examined from an extreme event attribution (EEA) perspective. This paper describes a set of studies that have examined the causes of extreme climate events using various general circulation models (GCMs), presenting a comprehensive methodology for GCM-based attribution of extremes of temperature and precipitation observed on large spatial and temporal scales in Australia. First, we review how Coupled Model Intercomparison Project Phase 5 (CMIP5) models have been used to examine the changing odds of observed extremes. Second, we review how a large perturbed initial condition ensemble of a single climate model (CESM) has been used to quantitatively examine the changing characteristics of Australian heat extremes. For each approach, methodological details and applications are provided and limitations highlighted. The conclusions of this methodological review discuss the limitations and uncertainties associated with this approach and identify key unexplored applications of GCM-based attribution of extremes. Ideally, this information will be useful for the application of the described extreme event attribution approaches elsewhere. [ABSTRACT FROM AUTHOR]

Mean and extreme northwest Australian (NWA) summertime rainfall has increased significantly since 1950. While previous studies have explored a range of possible factors impacting NWA rainfall, the causes of this increase and possible future changes remain uncertain. This study explores the increasing NWA summertime rainfall trends in Coupled Model Intercomparison Project phase 5 (CMIP5) models. By using a suite of models that contributed realizations of the historical period with various forcings, we explore the impact to this region of greenhouse gases and aerosol emissions since 1950 on mean rainfall and three extreme rainfall indices. The observed NWA rainfall trend is better captured in models when all forcings are included compared to simulations with only greenhouse gas forcing or with only natural forcing, although the models have a large spread. We hypothesise that anthropogenic aerosols played a major role in the observed rainfall trends, and the associated increase in monsoonal flow, and hence historicalNat and historicalGHG simulations tend not to capture observed rainfall trend. Throughout the 21st century, CMIP5 models simulate a stronger increase in mean summer precipitation and extreme indices of NWA rainfall in representative concentration pathway (RCP) 8.5 simulations than in RCP2.6. The NWA region shows intensified extreme events with fewer heavy precipitation days, but the reliability of these projections in this region should be further tested with estimates of future anthropogenic aerosol changes. Mean and extreme northwest Australian (NWA) summertime rainfall has increased significantly since 1950. The figure shows spatial trend of summer (DJF) wind at 850 hPa (m s−1 year−1) over the period 1950–2005 in (a) NCEP, (b) historical ensemble mean, (c) historicalAA ensemble mean, (d) historicalGHG ensemble mean in CMIP5 models. We hypothesise that the rainfall increase over NWA can be related to increased monsoonal flow due to increased aerosol emissions in last 56 years. [ABSTRACT FROM AUTHOR]

Explosive volcanism is an important natural climate forcing, impacting global surface temperatures and regional precipitation. Although previous studies have investigated aspects of the impact of tropical volcanism on various ocean-atmosphere systems and regional climate regimes, volcanic eruptions remain a poorly understood climate forcing and climatic responses are not well constrained. In this study, volcanic eruptions are explored in particular reference to Australian precipitation, and both the Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO). Using nine realisations of the last millennium (LM) (850-1850 CE) with different time-evolving forcing combinations, from the NASA GISS ModelE2-R, the impact of the six largest tropical volcanic eruptions of this period are investigated. Overall, we find that volcanic aerosol forcing increased the likelihood of El Niño and positive IOD conditions for up to four years following an eruption, and resulted in positive precipitation anomalies over north-west (NW) and south-east (SE) Australia. Larger atmospheric sulfate loading during larger volcanic eruptions coincided with more persistent positive IOD and El Niño conditions, enhanced positive precipitation anomalies over NW Australia, and dampened precipitation anomalies over SE Australia. [ABSTRACT FROM AUTHOR]

The article focuses on the Great Barrier Reef bleaching in Australia in 2016. Topics being presented include The integration of multiple interrelated factors by reef ecosystems which represents important considerations for attribution of bleaching and the application of a multifactor analysis of climatic and environmental influences contributing to the 2016 bleaching.

The skill of eight climate models in simulating the variability and trends in the observed areal extent of daily temperature and precipitation extremes is evaluated across five large-scale regions, using the climate extremes index (CEI) framework. Focusing on Europe, North America, Asia, Australia, and the Northern Hemisphere, results show that overall the models are generally able to simulate the decadal variability and trends of the observed temperature and precipitation components over the period 1951-2005. Climate models are able to reproduce observed increasing trends in the area experiencing warm maximum and minimum temperature extremes, as well as, to a lesser extent, increasing trends in the areas experiencing an extreme contribution of heavy precipitation to total annual precipitation for the Northern Hemisphere regions. Using simulations performed under different radiative forcing scenarios, the causes of simulated and observed trends are investigated. A clear anthropogenic signal is found in the trends in the maximum and minimum temperature components for all regions. In North America, a strong anthropogenically forced trend in the maximum temperature component is simulated despite no significant trend in the gridded observations, although a trend is detected in a reanalysis product. A distinct anthropogenic influence is also found for trends in the area affected by a much-above-average contribution of heavy precipitation to annual precipitation totals for Europe in a majority of models and to varying degrees in other Northern Hemisphere regions. However, observed trends in the area experiencing extreme total annual precipitation and extreme number of wet and dry days are not reproduced by climate models under any forcing scenario. [ABSTRACT FROM AUTHOR]

This study examines trends in the area affected by temperature and precipitation extremes across five large-scale regions using the climate extremes index (CEI) framework. Analyzing changes in temperature and precipitation extremes in terms of areal fraction provides information from a different perspective and can be useful for climate monitoring. Trends in five temperature and precipitation components are analyzed, calculated using a new method based on standard extreme indices. These indices, derived from daily meteorological station data, are obtained from two global land-based gridded extreme indices datasets. The four continental-scale regions of Europe, North America, Asia, and Australia are analyzed over the period from 1951 to 2010, where sufficient data coverage is available. These components are also computed for the entire Northern Hemisphere, providing the first CEI results at the hemispheric scale. Results show statistically significant increases in the percentage area experiencing much-above-average warm days and nights and much-below-average cool days and nights for all regions, with the exception of North America for maximum temperature extremes. Increases in the area affected by precipitation extremes are also found for the Northern Hemisphere regions, particularly Europe and North America. [ABSTRACT FROM AUTHOR]

Australia experienced much above average rainfall in association with strong, extended La Niña conditions during 2010-2012. Was the heavy Australian rainfall influenced by La Niña conditions and/or anthropogenic greenhouse gases? We investigate the relative contributions of anthropogenic climate change and natural climatic variability to the likelihood of heavy Australian rainfall using three distinct model datasets. Area-average rainfall anomalies for model simulations with natural forcings only were compared to simulations with both anthropogenic and natural forcings using 16 models participating in the Coupled Model Intercomparison Project Phase 5. Using fraction of attributable risk to compare the likelihood of unusual rainfall between the parallel experiments, we find attribution statements are uncertain, with FAR values sensitive to the attribution parameters considered, including thresholds, regions and seasons. When heavy rainfall probabilities were next investigated in ensembles of two atmospheric general circulation models, run with and without anthropogenically-induced sea surface temperature changes, results were model-dependent. Overall, the attribution of seasonal-scale heavy Australia rainfall to a particular cause is likely more complicated than for temperature extremes. As estimates of the greenhouse gas attributable change in rainfall risk may depend on the model datasets considered, it is also useful to consider model outputs from several datasets and using various estimates of counterfactual surface conditions to establish robust attribution statements for extreme rainfall events. In contrast, comparing the likelihoods of heavy rainfall during simulated La Niña years with El Niño/neutral years reveals a substantial La Niña influence on Australian rainfall during 2010-2012 that is robust to changes in the attribution framework. [ABSTRACT FROM AUTHOR]

Abstract: Both North and East Africa experienced more humid conditions during the early and mid-Holocene epoch (11,000–5000yr BP; 11–5ka) relative to today. The North African Humid Period has been a major focus of paleoclimatic study, and represents a response of the hydrological cycle to the increase in boreal summer insolation and associated ocean, atmosphere and land surface feedbacks. Meanwhile, the mechanisms that caused the coeval East African Humid Period are poorly understood. Here, we use results from isotope-enabled coupled climate modeling experiments to investigate the cause of the East African Humid Period. The modeling results are interpreted alongside proxy records of both water balance and the isotopic composition of rainfall. Our simulations show that the orbitally-induced increase in dry season precipitation and the subsequent reduction in precipitation seasonality can explain the East African Humid Period, and this scenario agrees well with regional lake level and pollen paleoclimate data. Changes in zonal moisture flux from both the Atlantic and Indian Ocean account for the simulated increase in precipitation from June through November. Isotopic paleoclimate data and simulated changes in moisture source demonstrate that the western East African Rift Valley in particular experienced more humid conditions due to the influx of Atlantic moisture and enhanced convergence along the Congo Air Boundary. Our study demonstrates that zonal changes in moisture advection are an important determinant of climate variability in the East African region. [Copyright &y& Elsevier]

Protracted dry periods lasting multiple years to decades have occurred in regions including southern Australia, the southwest United States and parts of the Mediterranean, since the latter part of the 20th century. Typically, these protracted droughts have been identified when a multi-year or decadal-scale average of precipitation or a hydrologic variable such as streamflow is well-below normal. However, we show that one of the most defining features of several of these recent protracted dry periods is not the presence of below or much-below average precipitation. Interestingly, most if not all of these protracted drought periods have the occasional year of near or above average precipitation. Rather, a distinct characteristic of recent protracted droughts is the absence of seasons or years of well-above average precipitation i.e. years or seasons of extreme precipitation. In this sense, we argue that extreme precipitation might be just as more important for determining the continuation of a drought as below average precipitation.To demonstrate the importance of considering extreme precipitation for understanding drought, we present a case study in southeast Australia for the so-called "Millennium Drought". The Millennium Drought was a persistent and prolonged dry period that began around 1997 and was predominantly characterised by the lack of autumn and winter precipitation. It is widely accepted that the Millennium Drought ended abruptly with the onset of strong La Niña conditions in 2010. However, we provide evidence that despite the high precipitation in the spring and summer of 2010, the anomalously dry conditions in autumn and winter never ceased and are not markedly different to those conditions observed during the Millennium Drought. This raises the question of whether the Millennium Drought ended, or whether it was just interrupted by the 2010 La Niña. Rethinking how we characterise protracted drought is critical given that those areas described previously in Europe, Australia and North America have experienced several "bursts" of multi-year drought in the last few decades. Establishing what characteristics of precipitation variability are important for these "bursts" – and whether they are caused by decadal-scale variability or a non-stationarity in precipitation associated with anthropogenic climate change – are key questions. [ABSTRACT FROM AUTHOR]