Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 334

launcher failure in 2005, CryoSat-2 was launched in April 2010 and, following in-orbit
testing, became operational in October that year. This will help corroborate results
from the Gravity Recovery and Climate Experiment (GRACE) satellite missions
(see section 5.3.2).
It is worth briefly summarising our current knowledge of the situation in Antarctica.
This is very important to sea-level rise and will affect low-lying regions worldwide,
although it is decidedly geology, not biology. There are broadly three Antarctic zones.
The East Antarctic (see Figure 5.9) contains some 90% of the continent's ice and this
is virtually (apart from a few small coastal areas) all land, and which is reasonably
stable but not immune to climate change. It is thought that this ice is getting thicker
because snowfall (precipitation) - although low - exceeds snow melt. The second area
is the Antarctic Peninsula which, as mentioned, sticks out away from the continent and
is sensitive to warming, with its marine shelves (resting on, or floating over, the sea
floor); this is particularly so on its eastern side. These include the Larsen ice shelves
that are being undermined by submarine currents from the east that have warmed a
little in recent decades (at a rate of around 0.01-0.02 ◦ C year − 1 ) and have recently
been subject to warmer surface air. Some of the peninsula's ice-shelf retreat is unique
to the current Holocene interglacial, although melt appears to have previously been
slower but continual over much of the Holocene. What is now known is that the
collapse of Antarctica's Larsen B ice shelf from the mid-1990s appears to have been
a unique event. One possibility was that the ice shelf may have collapsed previously
during other warm periods in the Holocene and then returned in cooler times. After
all, we know that the Holocene has had warm periods (such as the MCA or MWP) and
cooler times (such as the Little Ice Age); see Chapters 4 and 5. However, in 2005 the
results were published of research by geoscientist Eugene Domack and colleagues.
They analysed core samples taken in 2002 from various sites that had been beneath
the former ice shelf that had existed up to 2001. They also looked at a core taken
where the ice shelf had existed up to 1995. A few large boulders were also recovered
and only some showed evidence of recent colonisation by organisms. Carbon analysis
of these organisms gave modern 14 C ages (it was possible that older carbon could have
been recycled). Their conclusions, based on the biological and geological evidence,
was that the Larsen ice shelf had been in continual existence throughout the Holocene
interglacial. Its disintegration from the mid-1990s was therefore an event that had not
occurred since the last interglacial or earlier. Domack and colleagues said that the ice
shelf's demise was probably the consequence of long-term thinning (by a few tens of
metres) over thousands of years and of recent short-term (multi-decadal) cumulative
increases in surface air temperature that exceeded the Holocene's natural variation in
regional climate.
The third zone is the West Antarctic Ice Sheet, other than the Peninsula, which
consists of the Ross, Amundson and Weddell Zones. Of these, some of the Amundson
ice shelf has melted before in previous interglacials and so will play an important
part in near-future sea-level rise. Indeed, we know from foram remains under some
of the Amundson shelves that these have retreated in the past and reformed during
glacials. (The foram remains detected were from species that evolved in the past
600 000 years and so could not have been left over from before Antarctica began to
freeze a few million years ago.)