| answer text |
<p>In the Antarctic, there are two main forms of ice, glacial and sea ice, which,
due to differences in measurement approaches, are assessed separately.</p><p>Sea ice,
formed from freezing seawater, is highly variable on a year-to-year basis, and over
the last 5 years (2012 - 2016) the annual average extent of sea ice has decreased
by an average of about a quarter of a million square kilometres per year. In March
2017 the sea ice extent dropped to the lowest level observed since satellite monitoring
began in 1978— at about 2 million square kilometres, or 27% below the mean annual
minimum.</p><p>In the 5 years to mid-2016, around 550 Gigatonnes of glacial ice, which
is formed from snow, were lost from the ice sheet.</p><p>For a full understanding
of changes in Antarctic ice, longer-term trends should be assessed. The 5<sup>th</sup>
Assessment Report of the Intergovernmental Panel on Climate Change showed that the
Antarctic ice sheet has been losing mass over the past two decades and, while the
long term trend in Antarctic sea ice extent has shown a small increase, there are
strong regional differences, with extent increasing in some regions and decreasing
in others.</p>
|
|
