Update: New NASA map of sea ice minimum

Bad Astronomy
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Aug. 27 2012 12:12 PM

Update: New NASA map of sea ice minimum

Earlier, I wrote that arctic sea ice had yesterday reached record low levels, blowing through the previous lowest-seen minimum in 2007, even though there's still a lot of melting left to go.

NASA just released this visualization of the arctic region showing just how bad it is:

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Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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The white area is the extent of sea ice as of August 26, 2012. The orange line is the average minimum extent from 1979 - 2010, the time covered by satellite observations. In other words, every year they measure the outline of the ice when it reaches its minimum, usually in September, and then averaged those positions for that timespan.

As you can see, we've been well below the usual minimum ice extent for some time - not just where we usually are this time of year, but the actual minimum amount... and we still have weeks of melting yet to go.

I want to note that this does not necessarily mean we'll see sea level rising from this. That ice is floating on the water, and in general when ice melts the water level stays the same. You can see this for yourself: put ice in a glass, then fill it with water. Mark the level. Wait until the ice melts and you'll see the level hasn't changed. The ice displaces (pushes aside) an amount of water exactly equal to its own weight, so when it melts that water fills up the same volume the ice displaced. The level stays the same.

However, because ice is frozen fresh water, and the sea is salt water, floating ice may actually raise the sea level a bit. Still, the far bigger concern is ice on land that melts and flows into the ocean. That certainly can raise the sea level. Greenland has the second largest reservoir of frozen water on Earth, and it's seeing unprecedented melting.

So yeah, global warming is a concern, no matter how many people deny it. And it's not something we should blow off and worry about later. It's happening now.

Image credit: Scientific Visualization Studio, NASA Goddard Space Flight Center



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