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Earth Matters

Earth Indicator: 4 million

August 30th, 2012 by mscott

This week’s Earth Indicator is 4 million…as in 4 million square kilometers. It’s a number that scientists studying sea ice never thought they would see.

Every year, the sea ice at the top of our planet shrinks and grows with the seasons. But because ocean water lags behind the atmosphere in warming up and cooling down, Arctic sea ice reaches its maximum extent in March, and its minimum in September.

Since 1979, satellites have observed Arctic sea ice shrinking and growing, and scientists at the National Snow and Ice Data Center (NSIDC) have recorded the minimum and maximum extents, adding them to a growing archive of data about Earth’s frozen places. In tracking sea ice, NSIDC uses a five-day average to smooth out bumps in the daily sea ice extents. The numbers have been refined over time with the adoption of new processing and quality control measures, but the ballpark numbers have remained the same.

Ten years ago, NSIDC scientists noted that Arctic sea ice set a new record minimum at 5.64 million square kilometers on September 14, 2002. New records followed: 5.32 million square kilometers on September 22, 2005; and 4.17 million square kilometers on September 18, 2007. In August 2007, Arctic sea ice extent dropped so rapidly that it set a new record before the usual end of the melt season. (Researchers at the University of Bremen declared a new record in 2011, based on slightly different calculation methods.)

In the summer of 2012, not only was the 2007 record broken, but within days, the passed another barrier. As of August 28, 2012, the five-day running average of Arctic sea ice fell below 4 million square kilometers (1.54 million square miles). NSIDC director Mark Serreze remarked: “It’s like breaking the four-minute mile. Nobody thought we could do that, but here we are.”

Arctic sea ice extent graph. Courtesy National Snow and Ice Data Center.

But whereas the four-minute mile was a milestone of human achievement, 4 million square kilometers of sea ice is not so inspiring. “Arctic sea ice extent is declining faster than it used to, and we can expect a continuing decline overall, with some inter-annual variability,” said NSIDC lead scientist Ted Scambos. “We have a less polar pole.”

The low sea ice extent for 2012 fits within a larger pattern. For the past several years, September Arctic sea ice extent numbers have remained well below the 1979–2000 average of 6.70 million square kilometers. The low extent from 2012 is no outlier.

Arctic sea ice minimum extents (million square kilometers)

September 22, 2005: 5.32

September 17, 2006: 5.78

September 18, 2007: 4.17

September 20, 2008: 4.59

September 13, 2009: 5.13

September 21, 2010: 4.63

September 11, 2011: 4.33

Reflecting on sea ice extent falling below 4 million square kilometers, NSIDC scientist Walt Meier remarked: “It’s just a number, but it signifies a changing Arctic.”

Q & A: The Midwest Drought with Richard Seager

August 22nd, 2012 by Adam Voiland

This drought severity map was updated on August 21, 2012. It was generated by the National Drought Mitigation Center. For more information about the map, please visit this site.

NASA Earth Observatory writer Adam Voiland spoke with Columbia University climatologist Richard Seager about the widespread drought currently affecting North America. 

The current dry spell has been called a “flash drought.” Has it really come on that quickly or as a surprise?  
No, I wouldn’t say it has been a surprise to those of us who closely watch the seasonal annual forecasts and the La Niña and El Niño forecasts. I don’t think that’s something that has come across in a lot of the news coverage. It’s not like this has come on that quickly.

Remember all of those stories last summer about the drought in Texas? The drought did ameliorate some in the winter, but then the interior Southwest dried out, which is exactly what you would expect during a La Niña winter.  And then it really expanded north in the late winter, which was more surprising.  Now it’s gotten up into the Midwest and even up into New York where I am. I think the extension toward the Northeast, which is remarkable, has been caused by some random atmospheric variability that’s being added on to the forcing coming from the tropical Pacific Ocean.

A recent IPCC report on extreme weather events and climate change indicated that the link between climate change and droughts in North America isn’t straightforward. Do you think there is a link between the two?
I don’t think you can make a direct link because the natural variability is so tremendous. It is really hard to definitively detect human-induced changes for a specific region. Climate forecasts do predict that much of the southwest and the southern plains will get drier, but the human-induced component should be relatively small in comparison to the natural variability. However, we do have a background warming trend in the Southwest, so when these droughts come along, they happen in a warmer environment. That adds an extra layer of water stress. I do think that climate change plays an important role by making these La Niña-induced droughts worse than they otherwise would be.

Is the cause of this drought a lack of precipitation this summer or the lack of snowpack from the winter?
The lack of snowpack has definitely played an important role. Partly because of the La Niña, there was very little snow across the United States this past winter.  We had very little snow melt in the spring, so we entered the summer with much drier soil to begin with. That’s probably  contributing a positive feedback, in addition to the fact that the storm track has shifted way north.

August Puzzler Answer

August 21st, 2012 by Adam Voiland

Read our recent Image of the Day to find out more about the Yanqi Basin, the answer to August’s puzzler.  Congratulations to Yiannis Raftopoulos for being the first to identify the location.

We posted the mystery image on Monday at 6:17 p.m. and on our social media accounts on Tuesday morning. Within minutes of appearing on social media, Yiannis had worked out the answer. The lesson we take from this: the Yanqi Basin puzzler was a bit too easy.

So we ask you: what should we do to make this more challenging?  Do you have any suggestions for puzzler imagery?  (Write to us directly, so as not to spoil the idea for the rest of the readers.)  We will keep hunting for something that will stump you.

EO’s Satellite Puzzler: August 2012

August 13th, 2012 by Adam Voiland

Every month, NASA Earth Observatory will offer up a puzzling satellite image here on Earth Matters. The third puzzler is above. Your challenge is to use the comments section below to tell us what part of the world we’re looking at, when the image was acquired, and what’s happening in the scene. Bonus points if you can do it in less than 2 hours and 56 minutes—the amount of time it took Alex Mathieu to successfully solve our first puzzler.

How to answer. Your answer can be a few words or several paragraphs. (Just try to keep it shorter than 300-400 words). You might simply tell us what part of the world an image shows. Or you can dig deeper and explain what satellite and instrument produced the image, what bands were used to create it, and what’s interesting about the geologic history of some obscure speck of color in the far corner of an image. If you think something is interesting or noteworthy about a scene, tell us about it.

The prize. We can’t offer prize money for being the first to respond or for digging up the most interesting kernels of information. But, we can promise you credit and glory (well, maybe just credit). Roughly one week after a “mystery image” appears on the blog, we will post an annotated and captioned version as our Image of the Day. In the credits, we’ll acknowledge the person who was first to correctly ID an image. We’ll also recognize people who offer the most interesting tidbits of information. Please include your preferred name or alias with your comment. If you work for an institution that you want us to recognize, please mention that as well.

You can read more about the origins of the satellite puzzler here. Good luck!

Earth Indicator: 3σ

August 7th, 2012 by Adam Voiland

Is that a three omicron? Nope. Three, rho? Strike two. Our latest Earth Indicator is three-sigma.

In Greek, sigma (σ) is the 18th letter of the alphabet. In statistics, it’s a symbol for standard deviation, a measure of how spread out a set of data points are from the average (which is often called the mean by statisticians). Data with a low standard deviation indicates that the data points are bunched up and close to the mean. A high standard deviation indicates the points are spread over a wide range of values.

In a standard bell curve, most data points (68 percent) fall within one standard deviation (1σ) of the mean (see the pink section in the graph below). The vast majority (95 percent, the combined pink and red sections of the graph) fall within two standard deviations (2σ). An even higher percentage (99.7 percent, the combined pink, red, and blue sections) fall within three standard deviations (3σ) of the mean. Just a tiny fraction of points are outliers that are more than three standard deviations from the mean. (See the parts of the graph with arrows pointing to 0.15%).

Now imagine that instead of generic data points on a generic bell curve the values are actually measurements of summer temperatures. That will give you a foundation for understanding the statistical analysis that James Hansen published this week in the Proceedings of the National Academy of Sciences.

One of his main findings: as seen in the graph above, is that the range of observed surface temperatures on Earth has shifted over time, meaning that rare 3-sigma temperature events (which represent times when temperatures are abnormally warm) have grown more frequent because of global warming.

Here’s how Hansen puts it:

We have shown that these “3-sigma” (3σ) events, where σ is the standard deviation — seasons more than three standard deviations removed from “normal” climate — are a consequence of the rapid global warming of the past 30 years. Combined with the well-established fact that the global warming is a result of increasing atmospheric CO2 and other greenhouse gases, it follows that the increasingly extreme climate anomalies are human-made.

Want to learn more? A press release is available here. And Hansen has also published a summary of his paper (pdf) and an accompanying Q & A (pdf) that offer more details.


Moonlit Clouds Obscure Indian Blackout

August 2nd, 2012 by Mike Carlowicz

Earlier this week, as India endured the worst blackout in its history, many readers and members of the media asked us to show the vast country without lights. Just a few weeks ago, Earth Observatory showed the world what the Mid-Atlantic United States looked like before and after a massive storm-induced blackout. (We also showed the city lights of London.)

But this week, there was nothing to see…at least from space. Here is India before the blackout, as viewed through the day-night band of the VIIRS instrument on the Suomi-NPP satellite:

July 30, 2012

July 30, 2012

One night later, the view was not much better…

July 31, 2012

July 31, 2012

What’s the problem? It’s monsoon season in India, which means near-constant clouds and rain…and very little visibility for satellite instruments observing visible wavelengths of light.

Surely there is a blackout under those clouds, as nearly half of the nation (and 600 million people) went without power for parts of two days. You can catch a faint hint of more or less light between July 30 and 31 in the northeastern portion of the images. But mostly, the view is clouds, clouds, and more clouds. They are lit by moonlight, at least.