Antarctic Sea Ice

Guest post by Dr Jonathan Day, Department of Meteorology, University of Reading

What is going on with the Antarctic sea ice?

March 2017 was an interesting month for sea ice. Both northern and southern hemispheres experienced record breaking low extents for the time of year. The extent of Arctic sea ice reached the maximum area of its seasonal cycle on March 7th coming in at 14.42 million km2. This was a fraction below the previous record, set in 2015 and is in line with what we expect to see in a warming climate. Meanwhile the other side of the planet Antarctic sea ice continues to confound expectations.

Increasing Antarctic sea ice

Over the last 38 years the area covered by sea ice in Antarctica has been increasing slightly in all seasons, leading to record high conditions reported in 2015. This is not what one would expect in a warming climate. However, this year has gone in completely the other direction and on March 3rd the all-time record minimum of 2.11 million km2 was announced, about 25% below normal. So what does this all mean and why was the sea ice increasing despite global warming?

Firstly, one year, even a record breaker, doesn’t tell us a lot more than we knew before. We know that the magnitude of year-to-year variability of sea ice in Antarctica is very high compared to the long term trend [Fig 1].

Figure 1. February monthly mean Antarctic sea ice extent from NSIDC.

There are a number of competing theories as to why the ice has been increasing and these can be split into two categories:

  1. Changes associated with human activities;
  2. Natural variability.

Human activities causing changes in Antarctic sea ice

In the first category, physically plausible mechanisms have been proposed that link human activities associated with the creation of the ozone hole1 and increased runoff from the Antarctic ice sheets2 (land ice) to increased sea ice. However, different studies have come to different conclusions regarding the magnitude of these effects.

Natural variability in Antarctic sea ice

The second category relates to climate variability from natural causes. For example we know that the major modes of climate variability such as the El Nino Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) project strongly onto Antarctic sea ice variability. In addition, climate models and observations suggest that there may be modes of variability which act on multi-decadal timescales, although understanding of such modes is currently limited3.

Signal-to-noise ratio in sea ice changes

In order to detect the influence of climate change we need the signal caused by man-made changes to be large compared to natural variability. We can measure this ratio in climate model experiments and express it as a signal-to-noise ratio4. Climate models suggest that this ratio is small in the Southern Ocean compared to other parts of the world, therefore the signal of change may be drowned by the noise of variability [see the low values around Antarctica in Fig 2].

Figure 2. multi-model mean CMIP5 simulated change in air temperature over the 21st century divided by the simulated amplitude of natural variability – the signal-to-noise ratio (from Ed Hawkins).

Another line of evidence is that sea ice and temperature trends in the Southern Ocean changed sign in the 1970s for no apparent reason. The climate was generally warming from 1950-1978 and the cooling thereafter5 [Fig 3]. To me this is highly suggestive of natural multi-decadal variability, rather than a forced change6, but the jury is still out.

Figure 3. Southern Ocean SST and sea ice trends from HadSST, for the periods 1950-1978 (left) and 1979-2014 (right) and the zonal mean of both (middle) from Fan et al. (2014). Sea ice concentration is not available for the 1950-1978 period.

Is a signal starting to emerge?

Although one low year is not enough to tell if the sign of the trend is changing it is may be a sign that the climate change signal is starting to emerge from the noise of natural variability.

Will we enter another ice age?

There are a number of web and news articles around surrounding the question of whether or not we will enter another ice age. Many of these questions arise from the idea that a collapse or significant melting of the Greenland Ice Sheet will produce enough fresh water to shut down the global thermohaline circulation, dropping us into a new ice age in the next 10,000 years.

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The Pregnant Field Scientist

Last autumn, I had two great pieces of news. The first was that I had been awarded a small grant to conduct three weeks’ fieldwork in Chile. The second was that I was pregnant.

I was obviously immediately interested in other people’s stories about fieldwork while pregnant. I could find only a few blogs about it on the internet, so I thought I would write about my own experiences of fieldwork while pregnant.

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Software Sustainability Fellowship

SSII’m delighted to have been awarded a £3000 Software Sustainability Fellowship by the Software Sustainability Institute. This promises to be a great collaboration and I’m excited to be working with the SSI to promote sustainable software practices.

I plan to use the Fellowship funds to host a Software Carpentry Workshop at RHUL, and to attend a conference where I’ll promote sustainable software practices, including promoting open code.

For more information, please see the Fellowship Programme over at the SSI. You can read the profiles of the current and former Fellows here.

Where are the top geological sites in the UK?

As part of Earth Week 2014, the Geological Society ran a competition to find the UK’s top 100 Geosites. The competition can be followed on Twitter with the #100Geosites hashtag.

The results were published as an online clickable map and the results were highlighted on the BBC. This map is ideal for choosing your next UK holiday destination!

Not to be outdone, the Quaternary Research Association has highlighted, as part of its 50th Anniversary celebrations, the UK’s top 50 Quaternary sites. Again, this is presented as an online clickable map. Continue reading

Antarctic Peninsula has strong sensitivity to surface warming

The Antarctic Peninsula is warming very rapidly, about six times the global average[1-3]. There has been a 95% increase in positive degree day sums since 1948[4]. Glaciers in the region are accelerating, in response to frontal thinning and recession[5]. In addition, ice shelves are collapsing[6], glacier fronts are retreating[7]. The causes for much of these changes has often been attributed to ocean forcing, with warm ocean waters melting these glaciers from below[8-11]. However, while ocean forcing may dominate further south, such as at Pine Island Glacier, a few recent papers have highlighted the importance of surface processes and surface melt induced by warmer surface air temperatures and longer melt seasons, specifically on the Antarctic Peninsula. Continue reading

Books to read before starting University

Next week is Freshers’ Week and across the country, universities will be welcoming enthusiastic students into their departments. These students will be equipped with notebooks, lever-arch files, reading lists and text books.

But there is more that you can do to prepare for university. Here is my own recommended reading list. These are popular science books that I love. You won’t find them on your termly reading list, but they are well written by science advocates, and they may just remind you of your love of science after a particularly dull lecture. Further, they will broaden your horizons, going beyond the scope of your lecturer course and tying together many different concepts.

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Just published: most comprehensive review ever of the glaciation of Antartica

A major new review of the last glaciation of the entire Antarctic Ice Sheet has just been published by Quaternary Science ReviewsThe special issue of the journal includes a suite of review papers involving an international team of experts regarding the last glaciation of the entire Antarctic Ice Sheet. This review, which comprises six review papers and an overview paper in a special issue of Quaternary Science Reviews, is now complete and all papers have been accepted for publication. As this is the most important, up to date and inclusive review ever to be attempted for the glaciation and recession of the Antarctic Ice Sheet, it represents a major step forward in our understanding of palaeo ice-sheet dynamics, provides a benchmark against which future research needs can be identified and highlighted, and provides a compilation of data unlike anything seen before, which can be used to test and calibrate numerical ice-sheet models.

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How to get a funded PhD studentship

A position on a funded PhD studentship in the environmental sciences (including Geography and Geology) has never been easy, but in these days of funding cuts and university and RCUK (Research Council UK) reorganisations, it’s ever more difficult to get PhD funding. It’s competetive and every studentship may have hundreds of applicants. Here’s a guide on how to maximise your chances.

The following advice is most applicable to early career researchers wishing to pursue a PhD in Physical Geography or Geology, but hopefully some of it at least is more widely relevant! Continue reading

Moving on (again)

So, in September I’ll be moving on again. I’m leaving the Department of Meteorology at the University of Reading to take up a lectureship in Physical Geography (Quaternary Science) at Royal Holloway, University of London.

I haven’t been at the University of Reading for long, but I’ve been impressed by their progressive attitudes, by the friendliness of the Department for Meteorology (including their croquet games and daily seminars with cake!), and by their generally well-run, well-organised attitude. I enjoyed working on my research project and enjoyed working with my PIs. I’m very sad to be leaving.

But I’m also delighted to be starting at RHUL, to be joining such a dynamic and exciting department, and to be taking charge of my own research and teaching. It’s the next step in my academic career. I’m excited and can’t wait to start.