Arctic sea ice reached its annual minimum
extent September 19, and again on September 23, 2018.
NASA works with the National Snow and Ice Data Center to track sea ice in the Arctic.
Each year, it grows to a maximum extent through the winter
and shrinks to its minimum extent at the end of summer.
This year's minimum sea ice extent reached 1.77 million square miles.
It's tied with 2008 and 2010 as the sixth lowest
sea ice minimum since consistent satellite records began.
We need every single data point to string together into a really nice time series and that
helps us understand interannual variability and also the long-term trend.
NASA has been observing changes in the polar sea ice covers for over 40 years.
NASA studies the Arctic and Antarctic
sea ice covers in several ways. So NASA's Operation IceBridge,
it's an airborne mission – they fly every spring over the sea ice cover to measure the snow and the sea ice
And another way that we measure sea ice is using passive microwave.
So this is an instrument that can see through clouds essentially and tells us where the ice is.
In addition to the 40-year passive microwave record,
a new NASA satellite called ICESat-2 will provide a new
and important collection of sea ice observations.
ICESat-2 just launched and what it's measuring is really, really exciting.
So I was talking before about passive microwave tells us where the sea ice is.
What ICESat-2 is going to do is to tell us how thick the ice cover is.
It's measuring the freeboard of the ice cover; this is the amount of the ice that floats
above the sea level line, just like an ice cube in a glass of water, and we can use
that to calculate just how thick the underlying ice is.
Thickness is an important measure of sea ice health, and studying it
helps scientists understand how the Arctic is changing.
We're seeing a decline in sea ice thickness, in sea ice age, meaning that the ice
is no longer perennial, but it's transitioning more to seasonal type ice,
and also in its extentThere are two types of ice in the Arctic,
there's old ice and young ice. Perennial ice being the stuff
that lasts years, and then seasonal ice, the stuff that melts back
every summer. So there are some pretty big differences between those two ice types
Starting with the seasonal ice. This is the ice that forms when the
ocean freezes, so it actually has salt in it, it's very saline, because it'
forming from sea water. This stuff is usually thinner than the older ice
and because it has more salt, it's usually weaker in its structure,
so it's easier to break up. For the older ice, this stuff's
usually a lot thicker, a lot fresher and stronger, so it has more resilience
during the summer melt season than thinner ice.
With the successful launch of ICESat-2, NASA scientists will link the records of sea ice
extent, age and thickness to better understand
how Earth's polar regions are changing.
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