More ice than last year is still bad news for the Arctic
- 12 Sep 2013, 14:40
- Freya Roberts
Compared to last year, this summer's Arctic melt season has been
less severe - leading some people to claim sea ice is rebounding
from decades of thinning
shrinking. But as a look at satellite
data reveals, this year's ice cover is still tracking well below
average - meaning ice in the Arctic still faces long term
Summer sea ice
Based on the amount of ice present today, it's
unlikely the ice-covered area of ocean will shrink below last
year's record low. That area isn't expected to reach its minimum
for another week or two, but at the moment there's 5.14 million
square kilometers of ice. On the same date last year, just 3.51
millions square kilometers remained.
graph below shows how ice extent this year and last year
Scientists say the weather is the main reason
more ice has stuck around this summer.
Last summer was unusual - warm temperatures
helped melt the ice, while a
summer cyclone helped break the ice up and
disperse it. These weather conditions, plus the long term warming
trend, resulted in the
lowest levels of sea ice seen since satellite
records began in 1979.
Different weather patterns mean temperatures in
the Arctic have been much
cooler this summer, however, and have
meant less ice has broken up and drifted away.
Big year-to-year fluctuations in sea ice are
becoming commonplace in the Arctic, because recent decades of
rising temperatures have
thinned the ice, making it much
more vulnerable to changes in the weather. Even
though a layer of ice regrows each winter, it melts much more
easily under the right conditions in the summer.
Arctic ice decline continues
Despite the fact there's been some recovery, the
graph above also shows sea ice levels in the Arctic are still below
average this year. And that means the long term trend of sea ice
decline is continuing. There are a number of different ways of
measuring sea ice, and they all agree there's a downward
Probably the most commonly used measurement is
sea ice extent - the area of the ocean covered in ice, including
the bits where the ice cover is a bit patchy. Satellites have been
recording this information since 1979, and a number of
space & science
agencies keep track of it.
With maps and photos filling the gap back to
1953, this satellite data indicates Arctic sea ice has
been declining since at least the early 1950s:
Arctic sea ice extent relative to the 1981-2010
mean (marked as the x-axis). Source: NSIDC
In recent years, satellite missions calculating
the volume of sea ice have become popular. These satellites use
radars to measure the thickness of the ice - information which can
be combined with ice extent data to calculate volume.
Volume measurements give an even clearer picture
of how the Arctic is changing, because they tell you not just how
much ice is visible at the surface, but how deep that ice is
Brand new data from the European Space
Agency (ESA) shows that since its satellite missions began in 2010,
the volume of Arctic sea ice has been shrinking. As the video below
shows, sea ice cover is smaller and thinner in both winters and
NASA also ran a similar mission between 2003 and
2008 to map changes in sea ice volume. Over those five years,
NASA's satellites also
saw the Arctic ice shrink.
The drawback with ice volume data is that the
record is pretty short - NASA's mission ran for five years, and
ESA's has only been going for three so far. Eight years of data is
not really enough to look for trends.
The data helps scientists confirm that their
models of sea ice volume are doing a pretty good job of replicating
changes in the Arctic, however. The best known model of sea ice
volume, called PIOMAS,
agrees there's a long term decline:
Better than last year is still
skeptics suggested that because this year's
ice cover is higher than in 2012, Arctic sea ice is
rebounding.These claims ignore the fact that 'better than last
year' is still bad news, however.
As Carbon Brief
discussed earlier this week, satellite data
does show that in August 2013, Arctic sea ice extent average 2.35
million square miles. That's
919,000 square miles bigger than August last
year - an increase of about 60 per cent.
But as the ice volume and ice extent graphs
show, natural fluctuations in the climate mean sea ice cover
rise and fall from one year to the next
while still being in long term decline.
When Arctic sea ice reaches its annual low in a
few weeks time, it will still be well below average, and certainly
more worrying than terms like 'rebound' would suggest.