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. Graphic: Gergis, et al., 2016 / Journal of Climate

By Joelle Gergis
10 July 2016

(The Conversation) – In May 2012, my colleagues and I had a paper accepted for publication in the Journal of Climate, showing that temperatures recorded in Australasia since 1950 were warmer than at any time in the past 1,000 years.

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. [more]

How a single word sparked a four-year saga of climate fact-checking and blog backlash  

ABSTRACT: Multiproxy warm season (September–February) temperature reconstructions are presented for the combined land–ocean region of Australasia (0°–50°S, 110°E–180°) covering 1000–2001. Using between 2 (R2) and 28 (R28) paleoclimate records, four 1000-member ensemble reconstructions of regional temperature are developed using four statistical methods: principal component regression (PCR), composite plus scale (CPS), Bayesian hierarchical models (LNA), and pairwise comparison (PaiCo). The reconstructions are then compared with a three-member ensemble of GISS-E2-R climate model simulations and independent paleoclimate records. Decadal fluctuations in Australasian temperatures are remarkably similar between the four reconstruction methods. There are, however, differences in the amplitude of temperature variations between the different statistical methods and proxy networks. When the R28 network is used, the warmest 30-yr periods occur after 1950 in 77% of ensemble members over all methods. However, reconstructions based on only the longest records (R2 and R3 networks) indicate that single 30- and 10-yr periods of similar or slightly higher temperatures than in the late twentieth century may have occurred during the first half of the millennium. Regardless, the most recent instrumental temperatures (1985–2014) are above the 90th percentile of all 12 reconstruction ensembles (four reconstruction methods based on three proxy networks—R28, R3, and R2). The reconstructed twentieth-century warming cannot be explained by natural variability alone using GISS-E2-R. In this climate model, anthropogenic forcing is required to produce the rate and magnitude of post-1950 warming observed in the Australasian region. These paleoclimate results are consistent with other studies that attribute the post-1950 warming in Australian temperature records to increases in atmospheric greenhouse gas concentrations.

Australasian Temperature Reconstructions Spanning the Last Millennium



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