Author: avoiland

AGU2011: How Shifting Storm Tracks Are Amplifying Climate Change


Tropical cyclones and hurricanes generate the most headlines, but it’s mid-latitude storms churning through heavily populated parts of North America, Europe, and Asia that make the weather most of us actually experience.

Climate models predict that these mid-latitude storms should shift poleward and that the intensity and frequency of the storms could change as global temperatures rise, but actual evidence of such a shift has been difficult to pin down. However, a recently published analysis of 25 years of cloud data captured by satellites offers a compelling piece of evidence that suggests storm tracks are indeed shifting.

The research, led by (former) Scripps Institute of Oceanography scientist Frida Bender, shows that storms tracks have shifted poleward, narrowed, and grown less cloudy since 1983, particularly in the Southern Hemisphere. The analysis, based on data from the International Satellite Cloud Climatology Project, finds that storm tracks have shifted by about 0.4 degrees over the last 25 years.

What’s more, the analysis suggests that changes in the location and intensity of storms could amplify global warming. The researchers detected what amounts to a 2 percent decline in storm tracks over the 25 year record. The decline in cloudiness is of particular importance because it suggests that intensity of storms is likely decreasing. And since clouds reflect large amounts of sunlight, reduced cloudiness means that ocean surfaces beneath storm systems are likely growing warmer.

Graeme Stephens, the director of NASA’s Center for Climate Science at the Jet Propulsion Laboratory, underscored the importance of the study in a piece published by Nature Climate Change noting:

Bender and colleagues’ study reminds us of the importance of changes in the large-scale clouds associated with frontal storms in storm-track regions. Not only do the polewards shifts in storm-track location profoundly affect precipitation patterns in mid-latitude regions, but associated changes in cloudiness also exert a significant positive feedback on global warming.

Text by Adam Voiland. Frida Bender presented a poster about the topic  at an American Geophysical Union Meeting on Dec. 6, 2011. The full paper is available here. Video of Midwest tropical storm originally published by NASA’s Earth Observatory. 

AGU2011: What Would Pristine Air Mean for the Climate?

Imagine that all the aerosols (the miniscule particles of pollution, dust, sea salt, and many other things) floating around in the air over the United States suddenly disappeared. What would their absence mean for the climate? Loretta Mickley, a climatologist and aerosol expert from Harvard University, has tackled just that question by running a series of simulations with a high-resolution computer model developed at NASA’s Goddard Institute for Space Studies.

Her conclusion: the elimination of the particles would increase ground temperatures across the eastern United States, cause more springtime rain to fall, and drive an uptick in heat waves. All of this would be driven by something scientists call the “direct effect” of aerosols – the particles’ ability to warm or cool the atmosphere by either absorbing or scattering incoming energy from the sun. (In this case, the model didn’t account for the “indirect effects” of aerosols – how the particles affect clouds, a detail that can have an impact on how they affect the climate as well).

Atmospheric Environment published a study that details the experiments in July of 2011. Here’s how Mickley summarized the findings:

We find that removing U.S. aerosol significantly enhances the warming from greenhouse gases in a spatial pattern that strongly correlates with that of the aerosol. Warming is nearly negligible outside the United States, but annual mean surface temperatures increase by 0.4-0.6 K in the eastern United States. Temperatures during summer heat waves in the Northeast rise by as much as 1-2 K due to aerosol removal, driven in part by positive feedbacks involving soil moisture and low cloud cover. Reducing U.S. aerosol sources to achieve air quality objectives could thus have significant unintended regional warming consequences.

There’s good reason to consider how falling levels of aerosols will affect the climate. In the United States, several kinds of aerosol particles have actually seen their numbers fall steadily as regulations have gone into place to clean up the air for the sake of public health. Emissions of sulfur dioxide, for example, a gas produced by coal power plants that generates reflective sulfate particles has fallen by 83 percent since 1980.

Mickley presented her poster on Monday, Dec. 5, 2011. Text by Adam Voiland. Aerosols panel (from left to right:ash, pollen, sea salt, soot) published originally by NASA’s Earth Observatory. Lowerfigure courtesy of Loretta Mickley. 

To What Degree is Extreme Weather Linked to Climate Change?


As flood waters continue to inundate Thailand and drought parches Texas, the Intergovernmental Panel on Climate Change and Goddard Institute for Space Studies Director James Hansen have both released new statements about the connection between extreme weather and climate change. Although linking extreme weather to climate change has generated controversy in the past, both of the new reports point plainly to a connection.The IPCC, an international organizational that represents the scientific consensus of hundreds of leading climatologists, put it this way in the executive summary of its new report.

It is very likely that there has been an overall decrease in the number of cold days and nights, and an overall increase in the number of warm days and nights, on the global scale, i.e., for most land areas with sufficient data. It is likely that these changes have also occurred at the continental scale in North America, Europe, and Australia.There have been statistically significant trends in the number of heavy precipitation events in some regions. It is likely that more of these regions have experienced increases than decreases, although there are strong regional and subregional variations in these trends.

There is medium confidence that some regions of the world have experienced more intense and longer droughts, in particular in southern Europe and West Africa, but in some regions droughts have become less frequent, less intense, or shorter, e.g., in central North America and northwestern Australia.There is evidence that some extremes have changed as a result of anthropogenic influences, including increases in atmospheric concentrations of greenhouse gases. It is likely that anthropogenic influences have led to warming of extreme daily minimum and maximum temperatures on the global scale. There is medium confidence that anthropogenic influences have contributed to intensification of extreme precipitation on the global scale.

There is limited to medium evidence available to assess climate-driven observed changes in the magnitude and frequency of floods at regional scales because the available instrumental records of floods at gauge stations are limited in space and time, and because of confounding effects of changes in land use and engineering. Furthermore, there is low agreement in this evidence, and thus overall low confidence at the global scale regarding even the sign of these changes.


Meanwhile, Hansen has released the draft of a new paper (pdf) that also tackles the topic of extreme weather and climate. He’s somewhat less equivocal in his summary of the state of the science:

The “climate dice” describing the chance of an unusually warm or cool season, relative to the climatology of 1951-1980, have progressively become more “loaded” during the past 30 years, coincident with increased global warming. The most dramatic and important change of the climate dice is the appearance of a new category of extreme climate outliers. These extremes were practically absent in the period of climatology, covering much less than 1% of Earth’s surface. Now summertime extremely hot outliers, more than three standard deviations (σ) warmer than climatology, typically cover about 10% of the land area. Thus there is no need to equivocate about the summer heat waves in Texas in 2011 and Moscow in 2010, which exceeded 3σ – it is nearly certain that they would not have occurred in the absence of global warming. If global warming is not slowed from its current pace, by mid-century 3σ events will be the new norm and 5σ events will be common.

Text by Adam Voiland. Lead image of flooding in Ayutthaya published originally by NASA’s Earth Observatory. Extreme weather curves published originally by the IPCC. Land trends over land published originally on James Hansen’s Columbia University website. 

Pine Island Glacier: A Quest to Understand Antarctic Ice Loss

NASA recently posted a press release about an upcoming expedition to Pine Island Glacier Ice Shelf, a key piece of real estate in Antarctica that’s slipping into the ocean at an increasingly worrisome pace. This month, in fact, an aircraft participating in Operation IceBridge spotted a lengthy crack cutting across the massive sheet of floating ice. There wasn’t much room for many details in the release, so here’s a longer description of the upcoming expedition from Goddard’s cryosphere writer, María José Viñas, for polar science aficionados.


An international team of researchers will helicopter onto thePine Island Glacier ice shelf, one of Antarctica’s most active, remote andharsh spots, in mid-December — weather permitting. Their objective: to determinehow changes in the waters circulating under the fast-melting ice sheet arecausing the glacier to accelerate and drain into the sea.

If all goes to plan,the multidisciplinary group of 13 scientists, led by NASA’s emeritusglaciologist Robert Bindschadler and funded by the National Science Foundation(NSF) and NASA, will depart from McMurdo stationin mid-December and spend six weeks on the ice shelf. The team will use acombination of traditional tools and sophisticated new oceanographicinstruments to measure the ocean cavity shape underneath the ice shelf. Theyaim to determine how streams of warm water enter this cavity, move toward thevery bottom of the glacier and melt its underbelly, making it dump more than 19cubic miles of ice into the ocean each year.

“The project aims to determine the underlying causesbehind why Pine Island Glacier has begun to flow more rapidly and dischargemore ice into the ocean,” saidScott Borg, director of NSF’s Division of Antarctic Sciences, the group thatcoordinates all U.S. research in Antarctica on the southernmost continent and surrounding oceans.”This could have a significant impact on global sea-level rise over thecoming century.”


“Darn hard to get to”
Pine Island Glacier has long been on the radar screen of Antarcticresearchers.

“Once satellite measurementsof Antarctica started to accumulate and we began to see which places werechanging, this area lit up as a spot where there was a large change going on,”Bindschadler said.

Bindschadler was the first person to ever set foot on thisisolated, wind-stricken corner of the world in January 2008. Previously,scientists doubted it was even possible to reach the crevasse-ridden ice shelf.But Bindschadler used satellite imagery to identify an area where planes couldland safely.

“The reason we haven’t gone therebefore is that it’s so darn hard to get to,” Bindschadler said. “So provingthat landing was doable was a relief.”

The glaciologist’s joydidn’t last: the ground proved to be too hard for the planes transporting theinstruments to land repeatedly. Logistics experts determined they would have touse helicopters to transport scientists and instrumentation in and out the iceshelf, and the whole plan for field campaigns had to be redesigned around thehelicopters’ availability.

Almost four years after thisfirst landing, Bindschadler and his team will be returning to the ice shelf tostudy its innards.

Scientists have determined that it’s the interaction ofwinds, water and ice that’s driving ice loss. Gusts of increasingly stronger westerlywinds push the Antarctic Circumpolar Current’s cold surface waters away fromthe continent: then, warmer waters that normally hover at depths below thecontinental shelf rise. The lifting warm waters spill over the border of thecontinental shelf and move along the floor, all the way back to the groundingline—the spot where the glacier comes afloat— causing it to melt. The warmsalty waters and fresh glacier meltwater combine to make a lighter mixture thatrises along the underside of the ice shelf and moves back to the open ocean, meltingmore ice on its way out. But, how much more ice melts?  Bindschadler and his team need to findout to improve projections of how the glacier will melt and contribute to sealevel rise.

“All existing data (satellite images, variability of winds,submarine measurements) say this a highly variable system”, said Bindschadler.“But they’re all snapshots in time. Our team will be deploying instrumentationthat will get a longer record of the variability.”

Profiling oceanwaters
One of the first tasks for the teamwill be using a hot water drill to make a 500-meter deep hole through the iceshelf. Once the drill hits the ocean, the scientists will send a camera to peerinto the ocean cavity, observe the underbelly of the ice shelf and analyze theseabed lying 500 meters below the ice.

Then, they will lower a setof instruments that Tim Stanton, an oceanographer with the Naval PostgraduateSchool, has built. The primary instrument in the package is an ocean profiler, which will move up and down avertical cable that connects it to a communication instrument package on thesurface of the ice shelf. As it moves, the profiler will measure temperature,salinity and currents from 3 meters below the ice to just above theseabed. It can also be instructed to park at specific depths and gauge waterturbulence and vertical transport of heat and salt along the water column. Thedevice will send all data to the surface tower that will then transmit it toStanton’s laboratory via a satellite phone.

The profiler is controlled remotely, and Stanton can vary its sampling rate.It will initially do fast sampling,to observe daily changes in water properties and circulation withinthe ocean cavity.

“After about a month of fast sampling, we’ll make it reduce the numberof profiles it takes each day, to capture seasonal changes in water propertiesand circulation,” Stanton said. “If it survives its first year, we’ll switch tosuper slow sampling, to measure how much heat is coming into the cavity everyyear.”

A second holewill support another instrument array similar to the profiler but fixed toa pole stuck to the underside of the ice shelf. The fixed-depth flux packagewill make measurements very close to the interface where ice and water exchangeheat.

Another gadget connected tothe fixed-depth package will be a string of 16 small temperaturesensors deployed within the lowermost ice to freeze in and become part of theice shelf. Their mission: to measure the vertical temperature profile,data that can tell scientists how fast heat is transmitted upwards through theice whenever hot flushes of water enter the ocean cavity.

“Since the temperature of the ice shelf determines its strength, we hypothesizethat strength may decrease as warmmelting events occur within the ocean cavity,” Stanton said.
 
Stanton plans on deploying up to two sets of instruments during this fieldseason, and a third one next year. “If we get one in, I’ll be happy. If I get two, I’ll be extraordinarily happy,”he said. One of the biggest challenges in building his pack of instruments,Stanton said, was designing it to fit the hole in the ice shelf, only 20centimeters wide and 500 meters long. A tight, long hole also means that theteam will only get one shot at deploying the instruments: once the package islowered into the ocean cavity, it cannot be pulled out.
 
“I have been deploying instruments intoice floes in the Arctic for the last 10 years, so I got quite used tojust putting them in and turning on my heels and walking away. But it’s stillquite hard to do,” Stanton said.

Explosions and sledgehammers
A geophysicist with Penn StateUniversity, Sridhar Anandakrishnan, will create tiny earthquakes to studythe shape of the ocean cavity and the properties of the bedrock under the PIGice shelf. He will be doing measurements in about three-dozen spots in theglacier, using helicopters to hop from oneplace to another.
Anandakrishnan’s technique, formally called reflectionseismology, involves generating waves of energy by setting up small explosionsor by using instruments similar to sledgehammers to bang the ice. He’ll recordhow long it takes for the waves to travelthrough ice and water, bounce off the seabed and return, and he’ll analyze thestrength of the echo. Both factors will tell him about the thickness of the iceand water.

“[The technique] is identicalto the way bats and dolphins do echolocation: they send out a sound and listento the echo – both the time and direction of the echo tell them about thedistance to their prey,” he said.

Anandakrishnan also wants tostudy the properties of the bedrock beneath the ice.

“When glaciers are slidingover the bedrock, they do it very differently depending on whether it is roughor smooth,” he said.

Finally, the geophysicistwill inspect a mysterious ridge that runs across the ocean cavity under the icesheet. This ridge was unknown to researchers when they designed their projectin the early 2000s; it wasn’t until 2009 that an unmanned submarine operated bythe British Antarctic Survey detected it. Its existence has made the scientistsrethink where they will place their oceanographic instruments under the iceshelf, so that they don’t hit the ridge while the glacier advances toward thesea.

“ThePine Island Glacier ice shelf continues to be the place where the action istaking place in Antarctica,” Bindschadler said. “It only can beunderstood by making direct measurements, which is hard to do. We’re doing thishard science because it has to be done. The question of how and why it ismelting is even more urgent than it was when we first proposed the project overfive years ago.”

Text by Maria-José Viñas. Pine Island Glacier ice tongue image originally published on the Pine Ice Glacier Ice Shelf page. Image of Bob Bindschadler on the ice shelf originally published here. Ocean profiler image originally published on the Pine Island Oceanography Program website. Image of Sridhar Anandakrishnan originally posted by the National Science Foundation.

Why Ozone Monitoring Still Matters



Top scientists, policy makers and industry leaders are gathering in Washington this week for a four-day symposium that will feature discussions about the past, present and future health of the ozone layer. Some key questions on the agenda: To what degree are climate change and ozone depletion interconnected? And how can leaders apply lessons learned while confronting the ozone problem that dominated headlines in the 1980s to the threats posed by global climate change? In 1987, delegates from 24 nations signed the Montreal Protocol, a landmark piece of legislation that set limits on emissions of ozone-depleting substances known as chlorofluorocarbons (CFCs). Since then, every country in the world has followed suit. The video above shows what could have happened if countries had failed to regulate CFCs. But while the Montreal Protocol began the process of closing one chapter of the ozone story, the ozone layer still requires careful monitoring because other substances in the atmosphere – including climate-altering greenhouse gases – can also affect it. In the Q & A below, NASA Goddard atmospheric scientist Paul Newman offers his perspective on why the ozone story isn’t over, and how climate change will likely impact the evolution of the ozone layer in the future. To see daily updates on the health of the ozone layer, please visit Ozone Hole Watch.

The ozone layer is on the road to recovery. Why is it still such a hot topic among scientists?
It’s important to continue monitoring ozone because it’s so vital to life on Earth. Surface measurements and satellite observations confirm that ozone isn’t declining in our atmosphere anymore, so the Montreal Protocol is working. But ozone is impacted by many factors, not just CFCs. The Earth’s natural variations – like volcanic emissions, climate change, and the sun – can all impact ozone. Also, technological innovations like high-altitude aircraft or industrial chemicals can also impact it. So the ozone story isn’t over. It’s evolving.

If all of these factors influence ozone, can we say with certainty how it will change in the future?
The ozone layer is recovering from the effects of CFCs, but because of climate change, it will recover to different levels than its natural pre-industrial state. Our models show that we’re not going back to the old ozone layer, we’re going back to some new version of it. Our models also show that climate has a very different impact on ozone depending on whether you’re in the troposphere or the stratosphere.

What’s the difference between the troposphere and the stratosphere?
The troposphere is the lowest layer of our atmosphere, on average, extending up to about 7 miles above the Earth’s surface. Our day-to-day weather happens in the troposphere. The stratosphere extends from about 7 to 30 miles above the surface. While ozone is extremely important for screening harmful solar ultraviolet (UV) radiation, it’s a dangerous air pollutant at the Earth’s surface. Fortunately, about 90 percent of the planet’s ozone is in the stratosphere, while only 10 percent of is in the troposphere.



What about greenhouse gases? Do they also have different effects in the troposphere and stratosphere?
Greenhouse gases have much different effects in the troposphere and stratosphere. Carbon dioxide both absorbs and emits infrared radiation. In the troposphere, increased levels of carbon dioxide and other greenhouse gases block outgoing radiation, increasing the surface temperature. In the stratosphere, the increasing carbon dioxide concentrations allow greater radiation to space, cooling the stratosphere. So greenhouse gases warm the surface and cool the stratosphere.

How will climate change affect ozone in the stratosphere?
In the lower stratosphere, climate change will decrease the local ozone levels in the tropics and increase ozone in the mid-to-high latitudes. The “total ozone” will increase over its natural levels in the mid-latitudes in both the Northern and Southern Hemispheres – what some scientists call a “super recovery.”

How do you think the lessons learned from the ozone hole story are relevant to the climate change story?
There are two important science lessons from the Montreal Protocol. The first lesson is that solid science is the foundation for policy. The quality of both ground and satellite ozone observations can now detect a 1 percent change over a 10-year period. Policy makers relied on these estimates from scientists to formulate options on the regulation of ozone depleting substances. As the science evolved, the Montreal Protocol was strengthened. The science of climate change has seen similar improvements over the last few decades. Scientists continue to improve the quality of both observations and models of climate change. The improved quality of the science allows for the formulation of effective policy.

What’s the second lesson?
The Montreal Protocol demonstrates that the nations of the world can act together to solve a global problem. National boundaries are irrelevant to the stratospheric ozone layer. Emissions from countries in the Northern Hemisphere mainly caused the Antarctic ozone hole in the Southern Hemisphere. The nations of the world recognized the problem and acted together. This involved efforts between policy makers, technologists, scientists, industry, and non-governmental organizations. Technologies for replacing ozone-depleting substances have now been developed, and levels of these substances are now decreasing in our atmosphere. But we need to continue monitoring ozone and tracking how it reacts to climate gases. The story isn’t over.



Text by Alison Ogden. Videos from the Scientific Visualization Studio. Ozone vertical distribution graphic from Ozone Hole Watch. Image of Paul Newman originally published here.

NPP Launches: Put on Your Calibration and Validation Shoes



The NPOESS Preparatory Project (NPP), NASA’s newest Earth-observing satellite, roared into space on October 28th on a mission to improve understanding of how Earth’s climate (and weather) works by extending a variety of environmental data records established by an earlier generation of satellites.

There’s been plenty of good coverage of the hubbub and the careful engineering that goes into every NASA launch but less that gets into the nitty-gritty of the new science data that the satellite will provide.

What exactly will the mission’s science team do once NPP starts to produce data? What sorts of science issues will NPP-funded researchers tackle?

The answers to such questions are tucked away in a hard-to-find document (pdf) in the science section of NPP’s website. Though technical and filled with acronyms and jargon, it’s well worth reading if you want to understand what the NPP science team will be focused on in the coming months.

My four sentence summary: Teams of researchers charged with using NPP to monitor a whole slew of environmental phenomena (think, for example, atmospheric ozone levels, sea surface temperatures, cloud properties, fire activity, vegetation cover, ocean color, land surface temperatures, aerosol particles, snow cover, the planet’s albedo, and air pollutants such as sulfur dioxide) will be doing everything they possibly can to make sure the data NPP’s instruments provide can be merged seamlessly with measurements taken by an earlier generation of satellites. Sounds easy enough, I know. It’s not. Lots and lots of careful calibration and validation work is required because four of NPP’s instruments are significantly different than the instruments that preceded them.

To the NPP scientists about to embark on the task: Bon Voyage!


Text by Adam Voiland.  Launch #1 video published originally on Geeked on Goddard. Launch imagery available in the NPP press kit. Launch video #2 published originally by NASA Television’s YouTube Channel. 

What on Earth is That? #1

(Please post your guesses and your name in the comments, and we’ll give the answer next week…)

Here at What on Earth, we’re constantly stumbling across interesting photos, videos, and audio clips from NASA’s exploration of our planet (be it from space, the field, or the lab.) Whether it’s a satellite montage captured from thousands of miles up, the roar of our B-200 research aircraft, or a microscopic view of a cloud droplet, there’s literally always something strange and wonderful passing across our desks.

To have a little fun (and spare all that fascinating stuff from the circular file), we’re going to post snippets of it every now and then, usually on Fridays. What we post will change, but the question to you all will always be the same: “What on Earth is that?”

Our only hints:

  • Our picks will always be related to Earth science in one way or another, and…
  •  It will have some relation to what we do at NASA.

We’ll give you a week to post your guesses, and we’ll post the answer the following Friday.

***********************

Updated 7/16/2010

So, what on Earth was that? We received a barrage of thoughtful—and creative—responses that ranged from pollen, to DNA, to carbon nanodiamonds embedded in Antarctica ice. Ant-related answers were surprisingly common. (Nope, it isn’t an ant eating salt, spitting up acid, or laying eggs.) It is, drum roll please, a microscopic view of soot from wildfire smoke in Africa. Congratulations to posters MicroMacro (comment 121), Arbeiterkind (comment 124), Mike (comment 125), Michael & Marion Dreyer (comment 130), and Rosemary Millham (comment 141), who were correct or on the right track. A more complete description of the aerosols from this particular fire, including the image above, was published in the Journal of Geophysical Research (account required).

Here are a few more details to impress your pals: Bits of soot (a type of aerosol particle) tend to clump together into the chain-like structures visible above. Wildfires, diesel trucks, factories—anything that partially burns the carbon locked away in fossil fuels and organic materials can produce soot and release it into the air. Soot makes doctors nervous as it can cause health problems when it lodges in our lungs and works its way into our bloodstream. And climatologists are wary of the particles as well because they absorb the sun’s energy and hasten global warming and climate change by heating the atmosphere directly or coating the surface of glaciers. In recent years, black carbon is an active area of research in climate science, and it’s a target of study for a number of NASA’s Earth science projects, including the forthcoming Glory satellite. 


Image(left) from Peter Buseck, Arizona State University. Image(right) from Jim Ross, NASADryden Flight Research Center.

–Adam Voiland, NASA’s Earth Science News Team

NASA Scientist Wins Climate Communication Prize

Gavin Schmidt, a climatologist based at NASA’s GoddardInstitute for Space Studies (GISS) in New York City, has received the inauguralClimate Communications Prize from the American Geophysical Union, the largestassociation of Earth and planetary scientists in the world. The $25,000 prizewill be awarded at the group’s fall meeting in San Francisco thisDecember.  

Despite the rancor that often surrounds public discussions ofclimate change science, Schmidt has become one of NASA’s most valued andrelentless scientific communicators. He is regularly quoted by leadingnewspaper and magazine journalists, frequently offers his time and expertise atpublic events, and has appeared on numerous television programs. In his sparetime, he write for the widely read blog RealClimate and has published abook about climate change.

Here are a few links to interviews we’ve done with Schmidt in the past about communicating climate science and the surface temperature record. Also, take a look at these recent video interviews produced by Columbia and NASA and a few of Schmidt’s memorable appearances on CNN, the Daily Show, Nova, and Martha Steward (see 9:50). Congratulations, Gavin. And thank you. 

Text by Adam Voiland.

See This Year's Arctic Sea Ice Minimum


The National Snow and Ice Data Center (NSIDC) has tentatively announced that Arctic sea ice has reached its minimum extent for the year. From the NSIDC release:

The blanket of sea ice that floats on the Arctic Ocean appears to have reached its lowest extent for the year. Arctic sea ice extent fell to 4.33 million square kilometers (1.67 million square miles) on September 9, 2011. This year’s minimum was the second lowest in the satellite record, which started in 1979. The lowest extent was recorded in 2007.Over the last thirty years, ice extent, a two-dimensional measure of the ice cover on the Arctic Ocean, has declined in all months, with a more pronounced drop in summer. Scientists attribute this decline in large part to climate change. Arctic sea ice melts and refreezes in an annual cycle, reaching its lowest point in late summer, and its highest point in late winter.

Meanwhile, NASA Goddard Space Flight Center has posted HD video of the decline from the near maximum ice extent in early spring of 2011 through Sept. 9, 2011. The visualization (above) is based on data collected by Aqua’s AMSR-E instrument. From Goddard’s Flickr caption:

Sea ice goes through this shrink-and-swellrhythm every year, but since consistent satellite observations began in1979, both the annual minimum at the end of summer and the annualmaximum at the end of winter continue to decline in area and thickness.Consistent with rising temperatures globally and specifically in theArctic, climate scientists are concerned with this trend both as anindicator of climate change and as a feedback mechanism. As the white,highly reflective ice disappears, darker ocean waters appear. Thisdarker surface absorbs more solar radiation and acts as a positivefeedback to the warming that is already occurring and causing the changein the first place.

On Sept. 20th, NASA’s Cryosphere Program Manager, Tom Wagner, shared his take on Arctic sea ice with television audiences across the country.

Text by Adam Voiland. Visualization by the Scientific Visualization Studio based at Goddard Space Flight Center.