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| Re-analysed data shows that Australia has indeed been hotter over the past 30 years than any time in the preceding millennium. AAP Image/Dan Himbrechts |
Following the early online release of the paper, as the manuscript was being prepared for the journal's print edition, one of our team spotted a typo in the methods section of the manuscript.
While the paper said the study had used "detrended" data – temperature data from which the longer-term trends had been removed – the study had in fact used raw data. When we checked the computer code, the DETREND command said "FALSE" when it should have said "TRUE".
Both raw and detrended data have been used in similar studies, and both are scientifically justifiable approaches. The issue for our team was the fact that what was written in the paper did not match what was actually done in the analysis – an innocent mistake, but a mistake nonetheless.
Instead of taking the easy way out and just correcting the single word in the page proof, we asked the publisher to put our paper on hold and remove the online version while we assessed the influence that the different method had on the results.
Enter the bloggers
It turned out that someone else had spotted the typo too. Two days after we identified the issue, a commenter on the Climate Audit blog also pointed it out.
The website's author, Stephen McIntyre, proceeded to claim (incorrectly) that there were "fundamental issues" with the study. It was the start of a concerted smear campaign aimed at discrediting our science.
As well as being discussed by bloggers (sometimes with a deeply offensive and sexist tone), the "flaw" was seized upon by sections of the mainstream media.
Meanwhile, our team received a flurry of hate mail and an onslaught of time-consuming Freedom of Information requests for access to our raw data and years of our emails, in search of ammunition to undermine and discredit our team and results. This is part of a range of tactics used in Australia and overseas in an attempt to intimidate scientists and derail our efforts to do our job.
Bloggers began to accuse us of conspiring to reverse-engineer our results to dramatise the warming in our region. Former geologist and prominent climate change sceptic Bob Carter published an opinion piece in The Australian claiming that the peer-review process is faulty and climate science cannot be trusted.
Checking the facts
Meanwhile, we set about rigorously checking and rechecking every step of our study in a bid to dispel any doubts about its accuracy. This included extensive reprocessing of the data using independently generated computer code, three additional statistical methods, detrended and non-detrended approaches, and climate model data to further verify the results.
The mammoth process involved three extra rounds of peer-review and four new peer-reviewers. From the original submission on 3 November, 2011, to the paper's re-acceptance on 26 April, 2016, the manuscript was reviewed by seven reviewers and two editors, underwent nine rounds of revisions, and was assessed a total of 21 times – not to mention the countless rounds of internal revisions made by our research team and data contributors. One reviewer even commented that we had done "a commendable, perhaps bordering on an insane, amount of work".
Finally, today, we publish our study again with virtually the same conclusion: the recent temperatures experienced over the past three decades in Australia, New Zealand and surrounding oceans are warmer than any other 30-year period over the past 1,000 years.
Our updated analysis also gives extra confidence in our results. For example, as the graph below shows, there were some 30-year periods in our palaeoclimate reconstructions during the 12th century that may have been fractionally (0.03–0.04℃) warmer than the 1961–1990 average. But these results are more uncertain as they are based on sparse network of only two records – and in any event, they are still about 0.3℃ cooler than the most recent 1985–2014 average recorded by our most accurate instrumental climate network available for the region.
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| Comparison of Australasian temperature reconstructions. Red: original temperature reconstruction published in the May 2012 version of the study; green: more recent reconstruction published in Nature Geoscience in April 2013; black: newly published reconstruction; orange: observed instrumental temperatures. Grey shading shows 90% uncertainty estimates of the original 2012 reconstruction; purple shading shows considerably expanded uncertainty estimates of the revised 2016 version based on four statistical methods. The recent 30-year warming (orange line) lies outside the range of temperature variability reconstruction (black line) over the past 1,000 years. |
Our study now joins the vast body of evidence showing that our region, in line with the rest of the planet, has warmed rapidly since 1950, with all the impacts that climate change brings. So far in 2016 we have seen bushfires ravage Tasmania's ancient World Heritage rainforests, while 93% of the Great Barrier Reef has suffered bleaching amid Australia's hottest ever sea temperatures – an event made 175 times more likely by climate change. Worldwide, it has never been hotter in our recorded history.
Speed vs accuracy
There are a couple of lessons we can take away from this ordeal. The first is that it takes far more time and effort to do rigorous science than it does to attack it.
In contrast to the instant gratification of publishing a blog post, the scientific process often takes years of meticulous evaluation and independent expert assessment.
Yes, we made a mistake – a single word in a 74-page document. We used the word "detrended" instead of "non-detrended". Atoning for this error involved spending four extra years on the study, while withstanding a withering barrage of brutal criticism.
This brings us to the second take-home message. Viciously attacking a researcher at one of Australia's leading universities as a "bimbo" and a "brain-dead retard" doesn't do much to encourage professional climate scientists to engage with the scores of online amateur enthusiasts. Worse still, gender-based attacks may discourage women from engaging in public debate or pursuing careers in male-dominated careers like science at all.
Although climate change deniers are desperate to be taken seriously by the scientific community, it's extremely difficult to engage with people who do not display the basic principles of common courtesy, let alone comply with the standard scientific practice of submitting your work to be scrutinised by the world's leading experts in the field.
Despite the smears, a rummage through hundreds of our emails revealed nothing but a group of colleagues doing their best to resolve an honest mistake under duress. It wasn't the guilty retreat from a flawed study produced by radical climate activists that the bloggers would have people believe. Instead, it showed the self-correcting nature of science and the steadfast dedication of researchers to work painstakingly around the clock to produce the best science humanly possible.
Rather than take the easy way out, we chose to withdraw our paper and spent years triple-checking every step of our work. After the exhaustive checking, the paper has been published with essentially the same conclusions as before, but now with more confidence in our results.
Like it or not, our story simply highlights the slow and unglamorous process of real science in action. In the end, this saga will be remembered as a footnote in climate science, a storm in a teacup, all played out against the backdrop of a planet that has never been hotter in human history.
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