Arctic summer melt - which records are being broken?
- 21 Aug 2012, 14:50
- Carbon Brief staff
Every year, sea ice in the Arctic grows and shrinks with the
seasons. But it's also affected by other things like the weather,
which play a large role in explaining changes from year to year.
This means that although Arctic sea ice is
in long-term decline, that decline isn't uniform.
In 2007, the sea ice reached a record low - and since then a lot
of attention has been paid to the summer melt season. The Arctic
gets its fair share of misleading reporting, and with such a lot of
coverage in the run up to the September sea ice minimum it can get
confusing. To address this, we'll be regularly pulling together key
points from the best coverage on Arctic summer melting.
Here are the links for Tuesday 21st August
In anticipation of sea ice minimum headlines, it's worth noting
there are a number of ways to take
measurements of Arctic sea ice - we can look at sea ice extent,
area and volume.
Sea ice area is the ocean surface area that is
covered in ice, as measured by satellites. A more frequently used
term however is sea ice extent - which looks at
the area which is covered by some amount of ice, usually at least
15 per cent. This measurement therefore captures some open water
between ice floes.
Sea ice volume takes into account how thick the
ice is as well as the area it covers. That's important because
thinner ice is more vulnerable to change due to weather conditions.
While the long term warming trend can explain thinning, variable
weather conditions help explain how we can have record lows some
years and not others.
A number of institutions record these measurements, using
different techniques to compute the data collected by
satellites. Since there are many different data sets around, some -
say for sea ice area - might be broken while others might
not.
Getting this into context is important - as of yesterday, some
institutions reported new record
low for sea ice area since satellites began,
well before September when the minimum is usually reached. Records
held by the Arctic Regional Ocean Observing System (
ROOS) also indicate this to be the case.
But it will perhaps be more interesting to see if the record low
for sea ice volume is broken over the coming
weeks, given that
stormy conditions at the start of August this year may have
sizably affected ice which is becoming
increasingly thin over the long term. This however remains to
be seen.
Ted Scambos, of the National Snow and Ice Data Centre (NSIDC) which measures sea ice
extent,
reported yesterday that melting is likely to exceed the
previous record while the sea ice is still retreating, and that a
new ice extent daily record "would be likely by the end of
August".
Whether the sea ice reaches a new record low or not this year is
almost beside the point however. If we want to try and look at the
impacts climate change is having in the Arctic, it's the long term
trend which matters. And the long term trend is one of continuing
decline:
Fig. 1: Arctic sea ice volume anomaly from
PIOMAS 1979-2012. Shaded areas show one and
two SD from the trend.
Fig. 2: Arctic sea ice extent (July)
from
NSIDC - 1979-2012