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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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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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.

A note on ‘Collapse’

There is a lot in the media at the moment about the ‘collapse’ of the West Antarctic Ice Sheet. See my previous blog post for more information. But when we talk about ‘ice sheet collapse’, what do we actually mean? When we talk of people ‘collapsing’, they fall down right in front of us in the street. Buildings collapse. Bridges collapse. It’s a very bad thing. Right? Continue reading

GeoWomen

As part of GeoWeek, students and staff from Aberystwyth University Department of Geography and Earth Sciences discussed women in Geography and Geoscience. We wanted to know what challenges are faced specifically by women in science and by Geowomen, and how they can be overcome. We discussed our motivations and inspirations, gender balance in different research networks, challenges faced specifically by women in academia, and the importance of role models. Continue reading

The A to Z of Antarctica

Here is, hopefully, an informative and hopefully entertaining A to Z of all things Antarctic!

  •  A – Antarctica. The 5th largest continent in with world, with 26.5 million km3 of ice.
  • B – Beaker [slang]. A scientist who visits Antarctica to undertake research.
  • C – Cold. Antarctica has the coldest average temperature of any continent. The coldest temperature ever recorded on Earth was at Vostok: -89.2°C on 21st July 1983. Continue reading

AntarcticGlaciers.org – one year on

It’s one year almost exactly since AntarcticGlaciers went live at the start of July 2012. One year since I fumbled my way into this complex world of science communication. When I started out, I had little idea of what I was doing. I had never Tweeted (I viewed it rather as a waste of time), never made a website, and had never written for anyone other than academics and my peers. Continue reading

FieldPhotoFriday

I am on Twitter (@AntarcticGlacie). And so are many other field-based scientists. When I started using the hashtag #FieldPhotoFriday, so many people joined in that I had to storify it. We had photographs capturing a whole gamut of field experiences from a range of sciences. The places people go and what they get up to makes a great story. You can see the Storify from October 5th Here.