The melting and re-freezing of Antarctic ice sheets has always happened on a millennium time-scale. This time, we’re doing it in decades…
WHO: Robert Mulvaney, Richard C. A. Hindmarsh, Louise Fleet, Jack Triest, Louise C. Sime, Susan Foord (British Antarctic Survey, Natural Environment Research Council, Cambridge, UK)
Nerilie J. Abram (British Antarctic Survey, Natural Environment Research Council, Cambridge, UK and Research School of Earth Sciences, The Australian National University, Canberra, Australia)
Carol Arrowsmith (NERC Isotope Geosciences Laboratory, Keyworth, UK)
Olivier Alemany (Laboratoire de Glaciologie et Geophysique de l’Environnement (LGGE), Grenoble, France)
WHAT: Taking a giant (363.9m) ice core sample in Antarctica to look at climate history
WHEN: 6 September 2012
WHERE: Nature 489, September 2012
TITLE: Recent Antarctic Peninsula warming relative to Holocene climate and ice-shelf history (subs. required)
There’s been a lot of press recently about the Arctic Death Spiral which is of great concern to the stability of our climate, and means the poor southern cousin of the Arctic – the Antarctic doesn’t get much of a look in. No Santa, not as much media, what’s even happening with those penguins down south?
Well, it’s melting too, which is unsurprising given that the whole planet is heating up, but this group of British, Australian and French researchers have put together a short (~50,000 years) history of ice melt and temperature changes from their ice core. (How did the researchers know I did history AND science?!)
They drilled an ice core on James Ross Island that is 363.9m long (which gives a bit of perspective as to how much ice is in the Antarctic if it’s 363.9m deep!) and looked at the ratio of isotopes to work out what the climate and temperature was like. Isotopes are elements that are the same but have a different weight because of an extra neutron (the bits in an atom that have a neutral charge). Different isotopes occur naturally at different amounts – for instance, Carbon with a weight of 12 is the most common on earth and Carbon 13 (one neutron heavier) is found 1% of the time. This research looked at Hydrogen vs Deuterium isotopes.
Different isotope ratios can tell us what was and is going on in the atmosphere and 363.9m of ice core can tell us approx. 50,000 worth of history (the paper uses BP = before present. For some strange reason ‘present’ time is 1950, but then I guess BC and AD are just as arbitrary).
50,000 years BP was the last glacial interval before the Holocene, the current geological period we live in (although there’s an argument that we’re now living in the Anthropocene), all of which is in the ice core. There was a glacial maximum (26,000 – 20,000 years BP) which was 6.1C colder on James Ross Island than present and an early climactic optimum (warmest part) of the Holocene which was 1.3C warmer than present. Marine sediment samples show the ocean was 3.5C warmer.
Sustained warming on James Ross Island started occurring around 600 BP (1450AD for us) with a rate of .22C of warming per century. This cranked up with rapid warming between 1518 – 1621 and 1671 – 1777 of more than 1.25C.
The warming over the past 100 years has been the fastest warming seen in 2000 years, but it’s not yet out of the range of normal warming and cooling patterns for the Antarctic. However, the most recent phase of warming started in the 1920s (so will be more influenced by industrial and human pollution than the earlier warming) and it’s going at a rate of 2.6C per century. Which is double the rate of the natural warming above.
What does faster warming mean for Antarctic ice sheets? The rapid warming means the ice becomes unstable, and the researchers say that continued warming at the pace currently being observed could lead to an ice sheet collapsing. Additionally, if the warming continues, it will start melting the southern ice sheets that were stable in the earlier Holocene warm period.
So why should we, sitting at our computers a long way from the Antarctic care about melting ice sheets? Well other than the huge inconvenience that’s going to be for a whole range of cute animals like penguins whales and seals, melting ice sheets on land cause sea level to rise. The melting of the Arctic is certainly of concern for Northern Hemisphere weather patterns, but the melting of floating ice, doesn’t change sea level.
The melting of ice that is on an island does raise the sea level. And the melting of the entire Antarctic ice sheet would contribute an extra 60m to sea level. Which is horrifying, and a really good reason to care about the speed of melting in Antarctica. That kind of rise puts my hometown of Melbourne totally underwater (elevation 31m). It puts half of Vancouver underwater (elevation 0 – 152m) and all of London as well (elevation 24m).
Now, obviously the total melting of the Antarctic ice sheet is going to take a long time given how large it is. However, it’s really difficult to stop once started. And given that I keep talking about how climate change is going to be non-linear and unpredictable when feedbacks unexpectedly kick in from tipping points, I’d argue we shouldn’t be playing Russian roulette with this one and we should stop burning carbon instead.
[EDITED 21 Sept. to reflect the note from the lead author of the paper that an ice sheet is on land and an ice shelf is floating in water – AH]