Historical climate data can improve our assessment of future climate risk

Australia is a land characterised by dramatic climate and weather extremes. Currently, our understanding of the nation’s climatic history is mostly confined to official records kept by the Australian Bureau of Meteorology that begin in 1900, despite the fact that observations are available from first European settlement of Australia in 1788.

Colonial weather observations taken by government officials, farmers, doctors and weather enthusiasts– sometimes as often as five times a day – provide unparalleled opportunities to investigate past climate variability and extremes. The frequency and detail of these historical weather observations provide researchers with an exceptional record of Australia’s pre-1900 climate variability and its impact on past societies.

In Europe there is a long tradition of using historical records to reconstruct weather and climate, though in Australia these sources of climate history have been relatively untapped. In 2008, the South Eastern Australian Recent Climate History (SEARCH) project, developed and led by Joëlle Gergis, aimed to address this. It assembled an interdisciplinary team of climate scientists and historians to better understand Australia’s pre-1900 natural climate variability.

The SEARCH project was of global importance because so few historical instrumental records are located in the Southern Hemisphere. This makes extending the scientific understanding of long-term climate variability in the Australian region a high priority for international data recovery efforts.

​While the SEARCH project uncovered climate history long forgotten, it also laid important foundations for translating what Australia’s climate history might tell us about its future. This is the primary focus of our new initiative, Climate History Australia.

1905 snow mt Lofty
Snowballing in front of Mount Lofty House on Summit Road in Crafers (13km from the heart of Adelaide) in 1905. Recent research by our team shows less ‘snowy days’ are occurring in the Adelaide region. Source: South Australian Snow.

When it comes to climate change, Australia is the most vulnerable developed nation in the world. Nonetheless, assessment of climate risk is primarily derived from weather observations that begin in 1900. Climate History Australia aims to improve the assessment of future climate change risk by extending records of natural climate variability and weather extremes using pre-20th century sources.

Historical records from the 18th and 19th centuries provide a detailed picture of Australia’s pre-industrial climate before instrumental observations become influenced by global warming. This provides a unique opportunity to examine weather extremes produced purely by natural variability for comparison with recently observed variability and extremes. For example, our team recently published Australia’s longest daily temperature record beginning in 1838. This record from Adelaide in South Australia revealed a string of severe heatwaves and cold extremes, including rare snowfall events.

​One weather extreme of particular note was a heatwave that occurred in January 1858 that produced at least five consecutive days of temperatures greater than 40℃. Such an event would be newsworthy today, and a scan through the historical newspapers of the time reveal that it was very remarkable in the 1850s:

“Ordinarily we should leave it to a meteorological journal to chronicle the range of the thermometer and the moisture of the atmosphere just as the majority of persons would leave to meteorological observers the task of ascertaining such particulars. But when the heat has been so intense as to become the principal topic of conversation in every circle, and so persistent as to excite very general uneasiness and alarm, it forces itself upon the notice of the newspaper writer, and compels him to regard its influences as among the most important of passing affairs.” – Adelaide Observer, 6 February 1858

In fact, even in Adelaide’s modern climate record there have only been three other instances of five or more consecutive days above 40℃ (1908, 2009 and 2014). Many news stories detailing the 1858 heatwave detailed tales of people dying from extreme heat:

“Within the last week the mortality has been frightful in the extreme. Young children have been sufferers to a great extent; no less than nineteen… were the day before yesterday buried in the cemetery. But it has not been confined to them; hale men have been struck down by the effects of the sun, in other words by a coup de soleil.” – Adelaide Times, 30 January 1858

As contemporary climate researchers we are interested in asking: what if the same heatwave occurred today when global temperatures are now around 1.1℃ warmer than they were in 1858? Or, perhaps more importantly: what if that same heatwave occurs when global temperatures are 2℃, 3℃ or even 4℃ warmer than what they were in 1858? To answer these questions, we are combining state-of-the-art global climate models and various historical observations to quantify likely changes in Southern Hemisphere circulation patterns and associated climate and weather extremes.

​By estimating and modelling the impacts of past extremes only using post-1900 weather observations, Australia is very likely to be underestimating our climate risk. This would be devastating for a country that is already highly exposed to climate change.

A painting by J Hitchen depicting heavy snowfall on the Adelaide Hills from North Terrace, Adelaide, 1841. Source: B-7070 State Library of South Australia.

So far, we’ve focused our efforts on recovering high priority historical datasets that will become the longest daily weather records available from the Southern Hemisphere. These include weather journals from Perth in Western Australia that begin in 1830. There is another effort to fill a gap in the recently published daily record for Adelaide in South Australia starting in 1838.

To digitise these records, scans of the weather journals are uploaded to the citizen science platform Zooniverse for volunteers to transcribe. Zooniverse has proven to be an invaluable resource for weather data rescue activities. For example, a project led by Ed Hawkins from the University of Reading saw more than 16,000 volunteers digitise 5.25 million individual weather observations in only a few weeks – a Zooniverse record for participation in a project. So far, the Climate History Australia pilot project has attracted 731 volunteers who have transcribed 12,721 weather observations – a promising start for an overlooked region!

Once complete, these records will be continuous sub-daily datasets, providing a treasure trove for the study of Southern Hemisphere climate variability and extremes. Importantly, they will fill crucial data gaps in global datasets, improving the reliability of historical climate analysis. This will help improve future climate change risk assessment in regions like Australia that are highly exposed to weather and climate extremes. This will be all the more important as the planet continues to warm.

– Written by Zak Baillie and Dr Joëlle Gergis, Fenner School of Environment & Society, Australian National University (ANU).

This article was originally published by www.historicalclimatology.com on 5 October 2020. Climate History Australia’s Zooniverse project is now 92% complete, with over 1,000 volunteers who have classified more than 30,000 weather observations. Read the original article here.

A page from recently recovered weather journals from Adelaide, South Australia. The weather observations spanning 1843–1856 are currently being digitised on the Zooniverse citizen science platform to help create Australia’s longest daily weather record.
Source: National Archives of Australia.