On March 17, the Arctic region reached a milestone
…the second-lowest sea ice maximum extent since satellite measurements began.
The four lowest maximum Arctic extents on record have been in the last four years,
according to analysis from NASA and the National Snow and Ice Data Center.
This year’s maximum extent reached 5.59 million square miles.
But…what does that really mean?
How, and why, do we track sea ice?
We’ve got a good record of extents since the late 1970s.
So by now, the record of the Arctic ice is clearly
one of a decreasing ice cover.
To answer some of my questions, I talked with Dr. Claire Parkinson,
who has been studying sea ice from space for the past four decades.
I got a job at NASA’s Goddard Space Flight Center in July of 1978,
and I’ve been here ever since
and I’ve had the phenomenal opportunity of getting to start
when the satellite data were still fairly new and when,
at Goddard, people were trying to figure out
how to use the satellite data to reveal information about the Earth.
After several years when we started getting a longer record,
then our attention got changed into
“Well what kinds of trends are we seeing in sea ice?”
We’ve maintained this record of sea ice and we recognize now
that it’s very important for climate change,
because sea ice is one of the variables in the Earth system that has been changing
the most dramatically, especially in the Arctic.
But sea ice doesn’t just react to warming global temperatures…
it can actually accelerate the temperature increases.
Now the less sea ice coverage feeds back
into the warming, because if you’ve got less sea ice cover,
that means less of the sun’s radiation that comes down
to the surface will get reflected back.
Sea ice fluctuates with the seasons, growing during the cold,
dark winters until reaching an annual maximum extent
in February or March in the Arctic, and then shrinking through the summer
until reaching a minimum in September.
In the Arctic case, in late summer, it extends over about 5 million square kilometers.
In late winter, it extends way further, over about
15 million square kilometers, which is about one and a half times the area of Canada.
So studying sea ice
includes tracking how it changes seasonally. Rather than just looking
at the annual summer minimum, scientists track how the ice changes throughout the year,
to get a fuller picture of change.
Every month of the year has decreases in the Arctic and it doesn’t mean
every single year has less ice than the year before,
but it means that, overall, the trend is downward.