Considering both poles in February 2017, Earth essentially lost
the equivalent of a chunk of sea ice larger than Mexico, in contrast
to the average global minimum for 1981-2010.
Scientists at
NASA and the National Snow and Ice Data Center (NSIDC)
in Boulder, Colorado said on March 22, 2017 that Arctic sea ice
probably reached its 2017 maximum extent on March 7, and that this
year’s maximum represents another record low. Meanwhile, on the
opposite side of the planet, on March 3 sea ice around Antarctica
hit its lowest extent ever recorded by satellites at the end of
summer in the Southern Hemisphere. NASA called it:
… a surprising turn of events after decades of moderate sea
ice expansion.
Walt Meier, a sea ice scientist at NASA’s Goddard Space Flight
Center in Greenbelt, Maryland said:
It is tempting to say that the record low we are seeing this
year is global warming finally catching up with Antarctica.
However, this might just be an extreme case of pushing the
envelope of year-to-year variability. We’ll need to have several
more years of data to be able to say there has been a
significant change in the trend.
Satellites have been continuously
measuring sea ice in 1979, NASA said, and on February 13, the
combined Arctic and Antarctic sea ice numbers were at their lowest
point since.
On February 13, total polar sea ice
covered 6.26 million square miles (16.21 million square km). That’s
790,000 square miles (2 million square km) less than the average
global minimum extent for 1981-2010 – the equivalent of having lost
a chunk of sea ice larger than Mexico.
These line graphs plot monthly deviations and overall trends in
polar sea ice from 1979 to 2017 as measured by satellites. The
top line shows the Arctic; the middle shows Antarctica; and the
third shows the global, combined total. The graphs depict how
much the sea ice concentration moved above or below the
long-term average. Arctic and global sea ice totals have moved
consistently downward over 38 years. Antarctic trends are more
muddled, but they do not offset the great losses in the Arctic.
Image and caption via Joshua Stevens/
NASA Earth Observatory.
NASA explained the seasonal cycle of sea
ice’s growth and shrinkage at Earth’s poles, and described specific
weather events this year that led to the lower-than-average sea ice:
The ice floating on top of the Arctic Ocean and surrounding
seas shrinks in a seasonal cycle from mid-March until
mid-September. As the Arctic temperatures drop in the autumn and
winter, the ice cover grows again until it reaches its yearly
maximum extent, typically in March. The ring of sea ice around
the Antarctic continent behaves in a similar manner, with the
calendar flipped: it usually reaches its maximum in September
and its minimum in February.
This winter, a combination of warmer-than-average
temperatures, winds unfavorable to ice expansion, and a series
of storms halted sea ice growth in the Arctic. This year’s
maximum extent, reached on March 7 at 5.57 million square miles
(14.42 million square km), is 37,000 square miles (97,00 square
km) below the previous record low, which occurred in 2015, and
471,000 square miles (1.22 million square km) smaller than the
average maximum extent for 1981-2010.
Walt Meier added:
We started from a low September minimum extent. There was a
lot of open ocean water and we saw periods of very slow ice
growth in late October and into November, because the water had
a lot of accumulated heat that had to be dissipated before ice
could grow. The ice formation got a late start and everything
lagged behind – it was hard for the sea ice cover to catch up.
NASA also said the Arctic’s sea ice
maximum extent has dropped by an average of 2.8 percent per decade
since 1979. The summertime minimum extent losses are nearly five
times larger: 13.5 percent per decade. Besides shrinking in extent,
the sea ice cap is also thinning and becoming more vulnerable to the
action of ocean waters, winds and warmer temperatures.
This year’s record low sea ice maximum
extent might not necessarily lead to a new record low summertime
minimum extent, since weather has a great impact on the melt
season’s outcome, Meier said. But, he added:
… it’s guaranteed to be below normal.
There’s no real reason Earth’s poles should react in the same
way, or at the same rate, to global warming. A fundamental
difference between Arctic (left) and Antarctic (right) regions
is that the Arctic is a frozen ocean surrounded by continents,
while the Antarctic is a frozen continent surrounded by oceanic
waters. Map via NOAA/ climate.gov/
researchgate.net.
Meanwhile, in Antarctica, this year’s
record low annual sea ice minimum of 815,000 square miles (2.11
million square km) was 71,000 square miles (184,000 square km) below
the previous lowest minimum extent in the satellite record, which
occurred in 1997. NASA explained:
Antarctic sea ice saw an early maximum extent in 2016,
followed by a very rapid loss of ice starting in early
September. Since November, daily Antarctic sea ice extent has
continuously been at its lowest levels in the satellite record.
The ice loss slowed down in February.
This year’s record low happened just two
years after several monthly record high sea ice extents in
Antarctica and decades of moderate sea ice growth. The Arctic and
Antarctica are very different places; the Arctic is an ocean
surrounded by northern continents, while Antarctica is a continent
surrounded by ocean. In recent years, climage scientists have
pointed to this difference to help explain why the poles were
reacting to the trend of warming global temperatures differently.
But many had said they expected sea ice
to begin decreasing in Antarctica, as Earth’s temperatures continue
to warm.
Claire Parkinson, a senior sea ice researcher at Goddard, said
on March 22:
There’s a lot of year-to-year variability in both Arctic and
Antarctic sea ice, but overall, until last year, the trends in
the Antarctic for every single month were toward more sea ice.
Last year was stunningly different, with prominent sea ice
decreases in the Antarctic.
To think that now the Antarctic sea ice extent is actually
reaching a record minimum, that’s definitely of interest.
Bottom line: Considering both poles in
February 2017, Earth essentially lost the equivalent of a chunk of
sea ice larger than Mexico, in contrast to the average global
minimum for 1981-2010.