“There’s a lot of assertion [from sceptics] but I haven’t seen much science,” said Ayers. “If you are going to make claims then we need to do peer-reviewed science, not just assertion.”
In one paper, Ayers, who left the bureau 13 years ago, compared the Acorn-Sat warming trend with four other international data sets that use weather balloons, satellites and raw data from the bureau. In all cases, Ayers found a comparable warming trend.
One longstanding bureau critic is Dr Jennifer Marohasy of the rightwing Institute of Public Affairs – the Melbourne-based group that has been a central cog in attempts to deny or undermine human-caused climate change in the eyes of the public since the 1990s.
For several years, Marohasy has claimed the bureau’s practice of taking automatic measurements from the final second of each minute breached guidelines from the UN’s World Meteorological Organization, which recommends temperatures should be averaged over a minute.
But Ayers and the bureau say the response time of its automatic probes means the recorded measurement is effectively an average of the temperature over the previous 40 seconds to 80s.
In another study, Ayers examined if the bureau’s recording method could generate a bias towards higher temperatures.
Ayers took all the data recorded at two locations to see if taking extra readings across a minute made any difference to the temperatures recorded. While tiny differences were found, the study concluded the bureau’s method was “not at risk of bias”.
‘[Critics] never put their findings into reputable peer-reviewed journals’
Marohasy, and the Australian, have claimed the bureau’s methods contradict guidance from the WMO, despite previous studies arguing the contrary.
Dr Anthony Rea, a director at the WMO, says the organisation does not audit members but does produce guidelines “and members can implement these in different ways depending on their specific requirements”.
He says: “No measurement is perfect, the bureau’s temperature measurements included, but we all know there are multiple lines of evidence proving that global temperatures are rising, from satellites to ocean buoys to deep sea profilers. All evidence points in the same direction.”
Marohasy says her own analysis of three years of Brisbane airport temperature data shows automatic thermometers record warmer temperatures than parallel mercury probes 41% of the time and are cooler 26% of the time. This, she argues, means “future new record hot days could be a consequence of the probe rather than global warming”.
But scientists and the bureau say it was never possible – and it was never claimed by them – that mercury probes recorded the exact same temperatures as automatic probes.
The bureau has analysed the same Brisbane data, finding the maximum daily temperatures recorded manually by the “liquid-in-glass” mercury probes were on average only 0.02C cooler than automatic probes across three years. For minimum daily temperatures, the manual probes were 0.02C warmer than the automatic probes.
A bureau statement said: “There is no significant systematic difference in maximum and minimum temperatures, or the [daily] temperature range, or the effective response time of measurement, observed using mercury thermometers compared with platinum resistance probes.”
Gallant says: “I don’t even know what [the sceptics] are trying to highlight. That there are differences in measurements? We know that already and we take that into account.
“Some people might ask why can’t the temperature record be scrutinised? Scrutiny is part of the scientific process, but [critics] never put their findings into reputable peer-reviewed journals. The bureau has done this. Scientists have done this, and they all show the same thing.
“It’s just someone’s opinion until it’s published. That’s why I would argue this is harassment. They need to put up or shut up.”
The Guardian sent questions to The Australian, but did not receive a response.
In an 11-page response to questions, Marohasy defended her claims and said she intended to publish responses to the work of Ayers and to publish details of her current work on mercury probes with her IPA colleague, Dr John Abbot.
She said it was true that she had “pursued this issue with the bureau and some members of its staff for close to a decade”, adding: “But if they had acknowledged the genuine issue and the public interest in sharing the data, in say, 2015, we could have moved on.”
“There has been no harassment on our part,” she said. Because the bureau had initially refused to release the Brisbane data from mercury probes, leaving her and Abbot to resort to the Administrative Appeals Tribunal to get the information, “the harassment, obstruction and misinformation has been by the bureau”.