Understanding Climate Risk

Science, policy and decision-making

Antarctic Peninsula warms – The Australian spins

with one comment

Interesting ice-core temperature results from James Ross Island on the Antarctic Peninsula (AP) that points to recent and rapid warming that is unusual and of concern (sourced from Crikey who find its unusual nature alarming). The Australian reports (via Graeme Lloyd) that while unusual, the warming is not unprecedented relative to natural variation. Lloyd also includes a quote that is neither in the paper or the press release, and a bogus assertion arising from a misunderstanding of the purpose of the research. I have enquired from the authors if they were the source of Lloyd’s quote. Update – they have replied: see below.

So, how concerned should we be about the results? From the press release:

Results published this week (Nature paywall) by a team of polar scientists from Britain, Australia and France adds a new dimension to our understanding of Antarctic Peninsula climate change and the likely causes of the break-up of its ice shelves.

A core of ice was collected continuously through the James Ross Island ice cap, providing the first history of Antarctic Peninsula temperature changes since the last ice age. (Photo: Jack Triest)

A core of ice was collected continuously through the James Ross Island ice cap, providing the first history of Antarctic Peninsula temperature changes since the last ice age. (Photo: Jack Triest)

The first comprehensive reconstruction of a 15,000 year climate history from an ice core collected from James Ross Island in the Antarctic Peninsula region is reported this week in the journal Nature. The scientists reveal that the rapid warming of this region over the last 100 years has been unusual and came on top of a slower natural climate warming that began around 600 years ago. These centuries of continual warming meant that by the time the unusual recent warming began, the Antarctic Peninsula ice shelves were already poised for the dramatic break-ups observed from the 1990’s onwards.

The paper says that the Holocene high on the AP was 1.3±0.3°C warmer than present in the early Holocene (~11,500 years), consistent with other evidence in the region. During the Holocene, temperatures on the peninsula were around the 1961–1990 average. From 9,200 to 2,500 years before present (ypb) the temperature anomaly was 0.2±0.2°C. At around 2,500 ypb, temperatures “were on average 0.7±0.3 °C cooler than present between 800 and 400 yr BP (AD 1150–1550), and on a decadal timescale temperatures may have at times been more than 1.8±0.3°C cooler than present”.

The other thing the Nature paper did was look at rates of warming on a 100- and 50-year basis, concluding that rates on both scales were unusual but not unprecedented over the  past 2,000 years. The warming of 1.56°C over the past century is highly unusual (0.3%) over the past 2,000 years. The 50-year warming of 2.6 ± 1.2°C per century was similarly unusual.

So the recent warming has brought the AP back to temperatures where it was for most of the Holocene, with further warming in the pipeline. Recent ice-sheet collapses has shown the region’s ice is vulnerable to further warming:

The association between atmospheric temperature and ice-shelf stability in the past demonstrates that as warming continues ice-shelf vulnerability is likely to progress farther southwards along the Antarctic Peninsula coast to affect ice shelves that have been stable throughout the Holocene, and may make them particularly susceptible to changes in oceanographic forcing.

So what did Lloyd of The Australian say? He said the rise in temperatures was “within the bounds of natural climate variability over the past 600 years”. That is not a quote from either the paper or the press release.

It is true for the rate in rise, because checking the data (included in supplementary material published by Nature) shows that rises over the 17th century were comparable but it is not true for the magnitude of warming. So the statement is a reasonable interpretation of the data. But is it a quote? Lloyd didn’t speak to the authors and it is not in the text of the paper, so no, it isn’t a quote. The authors (via Narilie Abram of ANU) felt that Lloyd’s report was not technically wrong, but that a later AFP report published by the same paper was a better representation of their research.

This particular quote has been reproduced over a dozen times since the article on sites who maintain there is nothing to worry about. What is not reasonable is the next comment, this time Lloyd’s interpretation:

The research by Robert Mulvaney of the British Antarctic Survey, Cambridge, countered assumptions that human factors were responsible for the warming of the Antarctic ice shelf.

This is just not true, and is not  a reasonable interpretation of the article. It is rubbish. The study was not an attribution study (more on Real Climate – thanks Brian), it was looking at regional warming and assessing the implications of further warming for ice-sheet stability locally and further south. The other report in The Australian sourced from the AFP later that day had a very different take.

AN ice core extracted from an Antarctic islet has yielded further evidence of the impact of man-made warming on the frozen continent, fuelling concern for the future of ice shelves, a report said today.

The results “are consistent with a more rapid human-induced warming on top of a slower natural warming,” Robert Mulvaney, a researcher with the British Antarctic Survey (BAS), told AFP.

Now, that’s a quote. Nic Stuart, Canberra Times journo, also noted the difference.

Inclusion of the temperature data allowed me to look at its evolution using other methods. Step-change analysis of ten-year reconstructed temperatures allow large (century to millennial) shifts in climate regimes to be assessed. The following chart shows that the Holocene to about 2,250 years ago was very stable. This was followed by decreased temperatures reducing by about 0.4°C each time. An increase of 0.45°C 450 years ago led to natural warming upon which the anthropogenic warming of the late 20th and 21st century has been imposed.

Statistically significant (1% level) step changes in reconstructed 10-year temperature average for the James Ross Island core of Mulvaney et al (2012).

The period of cooling coincides with wetter conditions over southern Victoria that persisted for 2,000 years to AD1840. This is consistent with southern hemisphere weather systems extending further north under a cooler southern hemisphere climate, but may just be a coincidence. The rapid shifts in regional temperature are also consistent with changes noted in southern Victoria. The date of 600 years before present mentioned in the Nature paper as the beginning of the latest period of natural warming also coincides with dates for dune activation in Australia. Further research on regional changes over this period would be of great benefit as to how future climate may evolve.

My view is that energy held as heat in the Earth’s system can show trending or step-like behaviour. The reconstructed JRI temperatures appear to show both.

Updated August 27.

Advertisements

One Response

Subscribe to comments with RSS.

  1. Eric Steig at RealClimate points out that the Mulvaney et al study is not an attribution study. Theirs is a strictly limited view based on the ice core under examination.They report what has happened and point to where the next ice sheet decay is likely to occur. We should also be concerned about the undermining of Filcher-Ronne not far away.

    Brian

    August 27, 2012 at 1:55 am


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: