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:
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
I’ve been holding off writing about this until it was official, and now it is: the area of the arctic covered by sea ice has reached a record low.
[Click to embiggen.]
"Sea ice extent" is (more or less) a measure of the amount of ice covering the sea surface. It’s measured using satellite data; the area is divided into many bins, and sea ice extent is calculated by adding up all the bins with more than 15% ice in them. Every year the ice starts to grow in the autumn and melts in the summer, so you get a sine-wave curve of extent every year.
Satellite observations began in 1979. In the graph above, the dark line is the average summer extent for the period 1979 – 2000. The gray area around it is the measurement uncertainty (2σ if you want to be exact). The dashed green line is the extent for 2007 – the previous record low year – and the blue line is 2012. I added the red line so you can compare 2007 to now. The data numbers show the record is broken, though on the graph they look tied. [UPDATE: The new plot made by the NSIDC for August 26 clearly shows the extent is now lower than the lowest point in 2007.]
As you can see, we’re still on the way down, weeks ahead of the date of the lowest extent in 2007. The minimum extent in 2007 was reached on September 16. In 2011 – which had the second-lowest extent on record, essentially equaling that of 2007 – lowest extent happened on September 9. This year it was August 25.
Notice any trend there? I don’t want to make too much of the idea that it’s happening earlier every year because there aren’t enough data points, but it’s consistent with the Earth’s temperature increasing. The massive heat wave that melted so much ice in Greenland this summer may have something to do with this as well.
Here’s a map from the National Snow and Ice Data Center showing the extent for August 25, 2012. The orange line is again the average for August 25 taken over the years 1979 – 2000. White shows ice, blue is ocean, gray is land; you can see Greenland directly below the ice, with Canada and the US to the lower left. Obviously, the sea ice extent for August 25 is way, way below average compared to the past.
I’ll be honest: this map and graph are making me unhappy. The fantastic website Skeptical Science has more about this. The most worrisome aspect of this to me is how this accelerates. Ice is bright white, so it reflects sunlight. Sea water is much darker and absorbs that light. So the more ice you lose, the darker overall the arctic gets, and the faster it melts.
Of course; we’ll hear the usual excuses and cherry-picking from the denier set, but here are the facts:
The Earth is warming up. The rate of warming has increased in the past century or so. This corresponds to the time of the Industrial Revolution, when we started dumping greenhouse gases into the atmosphere. Greenhouse gases warm the planet (hence the name) — if they didn’t we’d have an average temperature below the freezing point of water. Carbon dioxide is a greenhouse gas which is dumped into the atmosphere by humans to the tune of 30 billion tons per year, 100 times the amount from volcanoes. And finally, approximately 97% of climatologists who actually study climate agree that global warming is real, and caused by humans.
Far from being a fluctuation, these records getting broken are more likely a trend, and it’s more likely we’ll see more of them.
Graph and image credit: National Snow and Ice Data Center
In late August, sea ice extent was way below average for that time of year, and it was predicted we were headed for at least a near-record low this year. Those predictions have, unfortunately, turned out to be true. On September 9, sea ice extent reached its yearly minimum, the second lowest since satellite records began in 1979 — and so close to the record low in 2007 that it’s a statistical tie.
NASA has posted series of pictures of sea ice this year taken by its Aqua Earth-observing satellite. Here’s the Arctic ice as it was in March (top) and September 2011 (bottom):
They put together a series of the images into an animation that really gives you a clear picture of what’s going on:
Of course, you expect more ice in the winter and less in the summer and fall, so by itself those pictures don’t tell you what this means. You need to compare the current extent with how things were in the past. As it happens, the National Snow and Ice Data Center in Boulder does just that.
Geez, I hate to keep hitting this theme, but y’know what? It’s important.
Using a fleet of Earth-observing satellites, the European Space Agency is reporting that the ice in the Arctic circle is already retreating considerably, and will once again be below average in extent this summer. This has been going on for a few years now, which isn’t terribly surprising considering that global warming is real and that we keep seeing recent years tied or exceeding records as hottest years on record.
Here’s the map they made showing sea ice extent from June 1 to August 24, 2011:
Yikes. Back in 2007, the Northwest Passage became entirely navigable by sea (without using an icebreaker ship) for the first time in recorded history. It had already been thinning for years, but an icebreaker ship was still needed to get through all of it — that’s changed now.
Moreover, it’s not just that the extent — that is, the amount of area covered by the ice — has dropped, it’s also that it’s thinning, dropping in volume. The ice volume has decreased by unprecedented amounts as well recently.
What does this mean for the current Arctic summer?
"The minimum ice extent is still three to four weeks away, and a lot depends on the weather conditions over the Arctic during those weeks," says Leif Toudal Pedersen, a senior scientist at the Danish Meteorological Institute. "Whether we reach an absolute minimum or not, this year again confirms that we are in a new regime with substantially less summer ice than before. The last five summers are the five minimum ice extent summers on record."
Just to be clear: it’s OK to question the science of global warming. It’s OK to question any scientific findings, as long as that questioning is done with good intentions and in good faith (so to speak). While poking around the web I found denier sites trying to confuse the issue of sea ice extent — for example, some talking about the navigability of the Northwest Passage as far back as 2000, but not mentioning you needed an icebreaker to do it.
As usual, the evidence here is pretty clear: temperatures are increasing, sea ice is going away, glaciers are retreating, ocean levels are rising, and all the while we’re dumping greenhouse gases into the atmosphere while the spin doctors whirl away.
It’s maddening. But it will continue, as surely as the Earth itself turns.
The report lists 15 key findings about the changes at the Earth’s northern regions. Fifteen. Here are four that alarmed me particularly:
1) The past six years (2005–2010) have been the warmest period ever recorded in the Arctic. Higher surface air temperatures are driving changes in the cryosphere.
3) The extent and duration of snow cover and sea ice have decreased across the Arctic. Temperatures in the permafrost have risen by up to 2 °C. The southern limit of permafrost has moved northward in Russia and Canada.
7) The Arctic Ocean is projected to become nearly ice-free in summer within this century, likely within the next thirty to forty years.
12) Loss of ice and snow in the Arctic enhances climate warming by increasing absorption of the sun’s energy at the surface of the planet. It could also dramatically increase emissions of carbon dioxide and methane and change large-scale ocean currents. The combined outcome of these effects is not yet known.
That last sentence is — pardon the expression — chilling. The real truth of this is we don’t know how this will affect the planet. We know what’s happening (sea levels are rising as the Earth warms, for example), and we have a good idea why it’s happening (despite deniers’ claims), but we don’t know the long-term effects. All we can say for sure is, they won’t be fun.
And speaking of deniers, a claim I’ve heard bandied about is that a single volcano eruption pours more carbon dioxide into the air than humans do over the course of a year (the time scale may vary depending on the claimant, but as you’ll see it doesn’t matter).
I know this isn’t strictly astronomy, but it’s a lovely time lapse video of sunrises and sunsets in the arctic… and since the Earth is tilted, in the summer the Sun skims just below the horizon as it circles the sky. So hey, I guess it is astronomy related!
You can really see this effect well starting at 1:06 into the video; the Sun sets at a very low angle to the ground, and comes right back up. The sky never gets completely dark.
The video was shot by a man who calls himself Mr. TSO, and he has many other lovely videos on Vimeo. It’s Friday, so take some time and look. You’ll breathe just a little bit easier if you do.
– Gorgeous Milky Way Time Lapse
– Very Large Telescope, Very Stunning Time Lapse Video
– Incredibly, impossibly beautiful time lapse video
– Dust, from the desert below to the galaxy above
– Stunning winter sky timelapse video: Sub Zero
– OK, because I like y’all: bonus aurora timelapse video
– AWESOME timelapse video: Rapture
The NASA Earth-science satellite Earth Observing-1 has returned another amazing picture: the calving of Petermann Glacier off Greenland. The break happened on August 5, and this shot was taken 11 days later:
The fjord is to the bottom, and the ice island that broke off is moving to the upper left. The picture is so clear and detailed that the scale is hard to determine by eye, but when you grasp it it’s mind-boggling: that chunk of ice is more than 25 kilometers long. That’s 15 miles.
Having a hard time grokking that? Here’s a picture of New York City to the same scale: