A historical perspective on Australian temperature extremes

Global temperature increases are most clearly detected in the shifting distribution of extreme events. Australia's warming climate has resulted in signifcant changes in the frequency of temperature extremes, with a general increase in heatwaves and a reduction in the number of cold days. Here, we present the longest historical analysis of daily Australian temperature extremes and their societal impacts compiled to date. We use a newly consolidated early instrumental dataset and a range of historical sources for the South Australia region of Adelaide-the nation's driest state, containing the most heatwaveafected city in Australia-to investigate any changes in the characteristics of daily temperature extremes back to 1838. We identify multidecadal variability in heatwave and snow event frequency with a peak in the early twentieth century, with an overall decrease in cold extremes and an increase in heatwaves in the region over the 1838-2019 period. Documentary and instrumental records show a decrease in the number of snow events in Adelaide, and a clear increase in the number of heatwaves since the late twentieth century. To gain dynamical insight into historical extremes in South Australia, detailed case studies are presented to compare the synoptic characteristics of historical hot and cold extremes and their impacts. We place a particular emphasis on lesser-known events of the pre-1910 period and rare low-elevation snowfall. Signifcantly, this is the frst study to provide long-term evidence for a reduction of low-elevation snow events and cold outbreaks in Australia. Finally, a discussion is provided on the value and limitations of using historical instrumental and documentary data to assess long-term changes in Australian temperature extremes and their potential to improve future climate change risk assessment

Climate indices in historical climate reconstructions:a global state of the art

Abstract. Narrative evidence contained within historical documents and inscriptions provides an important record of climate variability for periods prior to the onset of systematic meteorological data collection. A common approach used by historical climatologists to convert such qualitative information into continuous quantitative proxy data is through the generation of ordinal-scale climate indices. There is, however, considerable variability in the types of phenomena reconstructed using an index approach and the practice of index development in different parts of the world. This review, written by members of the PAGES (Past Global Changes) CRIAS working group – a collective of climate historians and historical climatologists researching Climate Reconstructions and Impacts from the Archives of Societies – provides the first global synthesis of the use of the index approach in climate reconstruction. We begin by summarising the range of studies that have used indices for climate reconstruction across six continents (Europe, Asia, Africa, the Americas, and Australia) as well as the world's oceans. We then outline the different methods by which indices are developed in each of these regions, including a discussion of the processes adopted to verify and calibrate index series, and the measures used to express confidence and uncertainty. We conclude with a series of recommendations to guide the development of future index-based climate reconstructions to maximise their effectiveness for use by climate modellers and in multiproxy climate reconstructions

Climate indices in historical climate reconstructions: a global state of the art

Narrative evidence contained within historical documents and inscriptions provides an important record of climate variability for periods prior to the onset of systematic meteorological data collection. A common approach used by historical climatologists to convert such qualitative information into continuous quantitative proxy data is through the generation of ordinal-scale climate indices. There is, however, considerable variability in the types of phenomena reconstructed using an index approach and the practice of index development in different parts of the world. This review, written by members of the PAGES (Past Global Changes) CRIAS working group – a collective of climate historians and historical climatologists researching Climate Reconstructions and Impacts from the Archives of Societies – provides the first global synthesis of the use of the index approach in climate reconstruction. We begin by summarising the range of studies that have used indices for climate reconstruction across six continents (Europe, Asia, Africa, the Americas, and Australia) as well as the world's oceans. We then outline the different methods by which indices are developed in each of these regions, including a discussion of the processes adopted to verify and calibrate index series, and the measures used to express confidence and uncertainty. We conclude with a series of recommendations to guide the development of future index-based climate reconstructions to maximise their effectiveness for use by climate modellers and in multiproxy climate reconstructions.The meetings that underpinned this article were supported by PAGES (Past Global Changes). The article processing charges for this open-access publication were covered by the Freigeist Fellowship “The Dantean Anomaly (1309–1321)” (funded by the Volkswagen Foundation) and the Education University of Hong Kong

An evaluation of the performance of the twentieth century reanalysis version 3

The performance of a new historical reanalysis, the NOAA–CIRES–DOE Twentieth Century Reanalysis version 3 (20CRv3), is evaluated via comparisons with other reanalyses and independent observations. This dataset provides global, 3-hourly estimates of the atmosphere from 1806 to 2015 by assimilating only surface pressure observations and prescribing sea surface temperature, sea ice concentration, and radiative forcings. Comparisons with independent observations, other reanalyses, and satellite products suggest that 20CRv3 can reliably produce atmospheric estimates on scales ranging from weather events to long-term climatic trends. Not only does 20CRv3 recreate a ‘‘best estimate’’ of the weather, including extreme events, it also provides an estimate of its confidence through the use of an ensemble. Surface pressure statistics suggest that these confidence estimates are reliable. Comparisons with independent upper-air observations in the Northern Hemisphere demonstrate that 20CRv3 has skill throughout the twentieth century. Upper-air fields from 20CRv3 in the late twentieth century and early twenty-first century correlate well with full-input reanalyses, and the correlation is predicted by the confidence fields from 20CRv3. The skill of analyzed 500-hPa geopotential heights from 20CRv3 for 1979–2015 is comparable to that of modern operational 3–4-day forecasts. Finally, 20CRv3 performs well on climate time scales. Long time series and multidecadal averages of mass, circulation, and precipitation fields agree well with modern reanalyses and station- and satellite-based products. 20CRv3 is also able to capture trends in tropospheric-layer temperatures that correlate well with independent products in the twentieth century, placing recent trends in a longer historical context.The research work of R. Przybylak and P. Wyszynski was supported by the National Science Centre, Poland (Grants DEC-2012/07/B/ST10/04002 and 2015/19/B/ST10/02933)

Inter-hemispheric temperature variability over the past millennium

The Earth’s climate system is driven by a complex interplay of internal chaotic dynamics and natural and anthropogenic external forcing. Recent instrumental data have shown a remarkable degree of asynchronicity between Northern Hemisphere and Southern Hemisphere temperature fluctuations, thereby questioning the relative importance of internal versus external drivers of past as well as future climate variability. However, large-scale temperature reconstructions for the past millennium have focused on the Northern Hemisphere, limiting empirical assessments of inter-hemispheric variability on multi-decadal to centennial timescales. Here, we introduce a new millennial ensemble reconstruction of annually resolved temperature variations for the Southern Hemisphere based on an unprecedented network of terrestrial and oceanic palaeoclimate proxy records. In conjunction with an independent Northern Hemisphere temperature reconstruction ensemble, this record reveals an extended cold period (1594-1677) in both hemispheres but no globally coherent warm phase during the pre-industrial (1000-1850) era. The current (post-1974) warm phase is the only period of the past millennium where both hemispheres are likely to have experienced contemporaneous warm extremes. Our analysis of inter-hemispheric temperature variability in an ensemble of climate model simulations for the past millennium suggests that models tend to overemphasize Northern Hemisphere–Southern Hemisphere synchronicity by underestimating the role of internal ocean–atmosphere dynamics, particularly in the ocean-dominated Southern Hemisphere. Our results imply that climate system predictability on decadal to century timescales may be lower than expected based on assessments of external climate forcing and Northern Hemisphere temperature variations alone.Laboratorio de Investigación de Sistemas Ecológicos y Ambientale

A climate reconstruction of Sydney Cove, New South Wales, using weather journal and documentary data, 1788–1791

This study presents the first analysis of the weather conditions experienced at Sydney Cove, New South Wales, during the earliest period of the European settlement of Australia. A climate analysis is presented for January 1788 to December 1791 using daily temperature and barometric pressure observations recorded by William Dawes in Sydney Cove and a temperature record kept by William Bradley on board the HMS Sirius anchored in Port Jackson (Sydney Harbour) in the early months of the First Fleet's arrival in Australia. Remarkably, the records appear comparable with modern day measurements taken from Sydney Observatory Hill, displaying similar daily variability, a distinct seasonal cycle and considerable inter-annual variability. To assess the reliability of these early weather data, they were cross-verified with other data sources, including anecdotal observations recorded in First Fleet documentary records and independent palaeoclimate reconstructions. Some biases in the temperature record, likely associated with the location of the thermometer, have been identified. Although the 1788-1791 period experienced a marked La Niña to El Niño fluctuation according to palaeoclimatic data, the cool and warm intervals in Sydney over this period cannot be conclusively linked to El Niño- Southern Oscillation (ENSO) conditions. This study demonstrates that there are excellent opportunities to expand our description of pre-20th century climate variability in Australia while contributing culturally significant material to the emerging field of Australian environmental history

The Industrial Revolution kick-started global warming much earlier than we realised

In the early days of the Industrial Revolution, no one would have thought that their burning of fossil fuels would have an almost immediate effect on the climate. But our new study, published today in Nature, reveals that warming in some regions actually began as early as the 1830s. That is much earlier than previously thought, so our discovery redefines our understanding of when human activity began to influence our climate

Placing the AD 2014-2016 'protracted' El Nino episode into a long-term context

Although extended or ‘protracted’ El Niño and La Niña episodes were first suggested nearly 20 years ago, they have not received the attention of other ‘flavours’ of the El Niño–Southern Oscillation (ENSO) or low-frequency ‘ENSO-like’ phenomena. In this study, instrumental variables and palaeoclimatic reconstructions are used to investigate the most recent ‘protracted’ El Niño episode in 2014–2016, and place it into a longer historical context. Although just reaching the threshold for such an episode, the 2014–2016 ‘protracted’ El Niño had very severe societal, agricultural, environmental and ecological impacts, particularly in western Pacific regions like eastern Australia. We show that although ‘protracted’ ENSO episodes of either phase cause similar, near-global modulations of weather and climate as during more ‘classical’ events, impacts associated with ‘protracted’ episodes last longer, with strong influences in eastern Australia. The latter is a response to the dominance of Niño 4 sea surface temperature (SST) and associated atmospheric teleconnection anomalies during ‘protracted’ ENSO episodes. Importantly, while Niño 4 SST anomalies recorded during the austral summer of 2016 were the highest values on record, an analysis of long-term palaeoclimate records indicates that there may have been episodes of greater magnitude and duration than seen in instrumental observations. This suggests that shorter instrumental observations may underestimate the risks of possible future ENSO extremes compared with those observed from multi-century palaeoclimate records. Improved knowledge of ENSO and the potential to forecast ‘protracted’ episodes would be of immense practical benefit to communities affected by the severe impacts of ENSO extremes.The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This work is part of the Atmospheric Circulation Reconstructions over the Earth (ACRE) initiative, and R.J.A. is supported by funding from the Joint BEIS/Defra Met Office Hadley Centre Climate Programme (GA01101). He also acknowledges the University of Southern Queensland, Toowoomba, Australia, and the Centre for Maritime Historical Studies, University of Exeter, Exeter, UK, where he is an Adjunct and Honorary Professor, respectively. J.G. acknowledges funding from Australian Research Council Project (DE130100668) and the ARC Centre of Excellence for Climate Extremes (CE170100023). R.D.D. is funded through NSF PIRE 1743738, PIRE: Climate Research and Education in the Americas using Tree-Ring/Speleothem Examples (PIRE-CREATE