Weather reports salvaged from ship logs are painting a new picture of the stormy conditions that battered the First Fleet during its epic voyage to Australia, more than 200 years ago.
They also reveal that Australia was experiencing a wetter than normal summer due to a La Niña event.
The findings were announced today as part of a media briefing by climate scientists at the Australian Science Media Centre.
"Historical data lets us know if current unusual events were also unusual in the past," says Dr Joëlle Gergis a climate scientist at the University of Melbourne.
She says consistent rainfall and temperature observations didn't begin in Australia until 1910, and air pressure readings weren't common until 1955.
Filling in the gaps
To fill in the gaps prior to this period climate scientists are currently undertaking a major international effort to recover lost weather data from historical sources, says Gergis.
The researchers hope to develop an historical database that will improve our understanding of weather pattern development and climate change, she says.
Gergis says researchers are finding weather data scattered in historical records such as newspapers, government correspondence, annual gazettes and almanacs. Millions of observations are also buried in the pages of ship logbooks and diaries of early European voyages.
She says this lets them see weather patterns over differing time scales, showing how things work in individual areas and how that interplay affects climate.
According to Gergis, the aim is to combine this information in a single database, that can be used to monitor climate change in a historical context.
Gergis says the meteorological observations of marine William Bradley on board the HMS Sirius in 1787, provide an insight into the violent conditions endured by the 1400 people aboard the First Fleet.
She says, the logs show they sailed in increasingly hot and humid conditions as they crossed the Atlantic Ocean from Portsmouth to Tenerife and Rio de Janiero, before arriving in Cape Town.
The favourable trade winds and ocean currents experienced in the Atlantic were replaced by the huge seas and violent winds of the roaring forties as they sailed east across the Indian and Southern Oceans.
"Big swells, storms and gale force winds ripped apart sails, flooded the holds and drenched those onboard," says Gergis. "Conditions were made worse because the waves washed away blankets, leaving people cold, as well as wet".
"New Year's Day 1788 was greeted by another storm and very cold weather around Tasmania, with reports of snow."
"More violent winds and storms lasting 10 days lashed the fleet as they sailed up the east coast."
La Niña event
Gergis says after landing in Botany Bay and finding no fresh water, the ships took several more days to get back out to sea, and sail north in to Port Jackson where conditions were better due to the wet weather at the time.
Thanks to the historical data, Gergis says we now know that at time of their landing, Australia experiencing a La Niña event, although other evidence from tree rings shows it was fairly weak.
She says we wouldn't have had this picture of the First Fleet without the ships logs of the weather on the journey.
According to Gergis it's too early to compare current climate change data with what we now know from the First Fleet records, but she adds "the further back you look the further forward you can see".