Naked Science Forum
Life Sciences => The Environment => Topic started by: paul.fr on 19/01/2009 17:11:45
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http://www.usgs.gov/global_change/glaciers/repeat_photography.asp
Glacier and Landscape Change in Response to Changing Climate
Repeat Photography of Alaskan Glaciers
Bruce Molnia
Repeat photography is a technique in which a historical photograph and a modern photograph, both having the same field of view, are compared and contrasted to quantitatively and qualitatively determine their similarities and differences. The following sections depict how this technique was used at a number of locations in Alaska, including Glacier Bay National Park and Preserve, Kenai Fjords National Park, and the northwestern Prince William Sound area of the Chugach National Forest, to document and understand changes to glaciers and landscapes as a result of changing climate. Through analysis and interpretation of these photographic pairs, information is extracted to document Alaskan landscape evolution and glacier dynamics for the last century-and-a-quarter on local and regional scales and the response of the Alaskan landscape to retreating glacier ice.
This images used on this Web site are available for public domain and do not require permission from the U.S. Geological Survey for use. See USGS Policy -- Copyrights and Credits for additional information on crediting the USGS.
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This warming of the planet is probably worse than a lot of the public think it is.
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But if you did not care, you could go on a fossil fuel-powered Alaska cruise (see google ad below) and see glaciers and the effects of global warming for yourself. You even get 75% off!
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Hahaha! Why don't I get an ad for that Alaska cruise! [:(][:(]
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The ad was there two times. Now it is gone. The ads change. Maybe it will come back.
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They're not coming back! All I'm getting is dating sites!!!
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Here it is again!
75% off Alaska Cruises
Huge selection of discounted Alaska cruises. All cruise lines.
AlaskanCruise.com
And a new one that matches:
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Alaska Glacier Cruises
Looking for Alaska Glacier Cruises? See Alaska Glacier Cruises.
azumano.com
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Nope, I haven't got anything like that, we must have different ads.
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Posted by: JeffMasters, 4:03 PM GMT on January 12, 2009
The top climate story of 2008, as it was in 2007, was the extraordinary summertime sea ice retreat in the Arctic. For the second consecutive year, we experienced the opening of the fabled Northwest Passage through the Canadian Arctic waters. Explorers have been attempting to sail the Northwest Passage since 1497, and 2007 and 2008 are the only known years the passage has been ice-free. In addition, 2008 saw the simultaneous opening of the Northeast Passage along the coast of Russia. This meant that for the first time in recorded history, the Arctic ice cap was an island--one could completely circumnavigate the Arctic Ocean in ice-free waters. Although the summer ice extent in 2008 finished 9% higher than 2007's record minimum, it was still an extraordinary 34% below average, according to the National Snow and Ice Data Center. Furthermore, the ice was thinner at the September 2008 minimum compared to 2007, so the total ice volume (thickness times area) was probably at its lowest point in recorded history in 2008.
Figure 1. Daily arctic sea ice extent for September 12, 2008. The date of the 2008 minimum (white) is overlaid on September 16, 2007--last year's minimum extent (dark gray). Light gray shading indicates the region where ice occurred in both 2007 and 008. Image credit: National Snow and Ice Data Center.
The Arctic "perfect storm" of summer weather in 2007 did not repeat in 2008
The summer of 2007 saw a "perfect storm" of weather conditions favorable for ice loss. Unusually strong high pressure over the Arctic led to clear skies and plenty of sunshine. Arctic winds, which usually blow in a circular fashion around the Pole, instead blew from the south, injecting large amounts of warm air into the Arctic. How unusual were these conditions? Well, at last month's meeting of the American Geophysical Union, the world's largest scientific conference on climate change, J.E. Kay of the National Center for Atmospheric Research showed that Arctic surface pressure in the summer of 2007 was the fourth highest since 1948. Cloud cover at Barrow, Alaska was the sixth lowest. This suggests that once every 10-20 years a "perfect storm" of weather conditions highly favorable for ice loss invades the Arctic. The last two times such conditions existed was 1977 and 1987.
The 2008 melting season began in March with slightly greater ice extent than had been measured in previous years, thanks to a relatively cold winter during 2007-2008. However, since so much ice had melted during the summer of 2007, most of the March 2008 ice was thin first-year ice, which extended all the way to the North Pole. The total ice volume in the Arctic in March 2008 was lower than what the record-breaking year of 2007 had seen. This led to speculation that a new record minimum would be set in 2008, and Santa's Workshop would plunge into the ocean as ice melted at the North Pole. However, the "perfect storm" of summertime weather conditions did not materialize in 2008. From May through July, cooler temperatures and winds less favorable to ice loss occurred. When very warm temperatures moved into the Arctic in August, the ice loss rate accelerated to levels higher than in 2007. However, with sunlight waning, ice loss was not able to reach the levels seen in 2007. Arctic temperatures in the summer of 2008 were up to 4°C cooler along the Siberian coast than in 2007 (Figure 2).
Figure 2. Difference in surface temperature (°C) between the summer of 2008 and the summer of 2007. Blues and purples indicate areas where is was cooler in 2008. The biggest change was over the Bering Sea between Alaska and Russia, where exceptionally sunny weather with southerly winds in 2007 caused record-breaking warmth. Image credit: NOAA/ESRL.
The future of arctic sea ice
Climate models have done a poor job predicting the recent record loss of arctic sea ice (Figure 3). None of the models used to formulate the official word on climate, the 2007 United Nations IPCC report, foresaw the shocking drop of 2007-2008. At the December 2008 AGU meeting, Wieslaw Maslowski of the Navy Postgraduate School hypothesized that the reason for this was the models' improper handling of ocean currents and how they transport heat. He blamed 60% of the melting during the past decade on heat brought in by ocean currents, and projected that summertime arctic sea ice would completely disappear by 2016. Dr. Jim Overland of NOAA's Pacific Marine Environmental Laboratory was more conservative, projecting a 2030 demise of arctic sea ice. He thought we would be "hanging around where we are for a while", and thought it would take two more unusual summers like the "perfect storm" of 2007 to push the system to an ice-free state. He further noted that while summertime air temperatures have been near record levels the past few years in the Arctic, there has been one period of comparable warmth, in the 1930s and 1940s. The year 1941 still ranks as the warmest year in the Arctic, though 2007 was virtually tied with it. However, the warmth of the 1930s and 1940s was different than the current warming, and was caused by the Siberian High moving unusually far east over Europe, driving warm, southerly winds over Greenland. The warmth in the past decade, in contrast, is associated with a warming of the entire planet, and is not due to an unusual pressure pattern driving warm air into the region. This means that the current warming is accompanied by much warmer ocean waters, which have helped caused much of the arctic sea ice loss the past two years by melting the ice from beneath.
Figure 3. Arctic sea ice extent from observations (thick orange line) and 13 model forecasts used to formulate the 2007 IPCC report (light lines). The thick black line is the multi-model ensemble mean, with the standard deviation plotted as a dashed black line. Image has been updated to include the observed 2007 and 2008 measurements. Image credit: Arctic sea ice decline: Faster than forecast by Stroeve et al., 2007.
The impact on the jet stream
The unprecedented melting of arctic sea ice the past two summers has undoubtedly had a significant impact on the early winter weather over the Northern Hemisphere. Several modeling studies presented at the December AGU meeting showed that sea ice melt on this scale is capable of injecting enough heat into the atmosphere to result in a major shift in the jet stream. Dr. Overland remarked that the early cold winter over North America this winter, and the exceptionally cold and snowy early winter in China last winter, were likely related to arctic sea ice loss. The sea ice loss induced a strong poleward flow of warm air over eastern Siberia, and a return flow of cold air from the Pole developed to compensate. Thus regions on either side of eastern Siberia--China and North America--have gotten unusually cold and snowy winters as a result.
The impact on sea level rise
The loss of arctic sea ice will have little impact on sea level rise over the next few decades. Since the ice is already floating in the ocean, melting it does not change sea level much--just like when ice melting in a glass of water will not change the level of liquid in the glass. In the case of sea ice, there is a slight sea level rise, since the fresh melt water is less dense than the salty ocean water it displaces. If all the world's sea ice melted, it would raise global sea level by only 4 mm. This is a tiny figure compared to the 20 feet of sea level rise that would occur from complete melting of the Greenland ice sheet--which is on land.
The impact on melting of the Greenland Ice Sheet
The big concern with arctic sea ice melt is the warmer temperatures it will bring to the Arctic, which will bring about an accelerated melting of the Greenland Ice Sheet. As the sea ice melts, the resulting warmer average temperatures will increase the amount of dark, sunlight-absorbing water at the pole, leading to further increases in temperature and more melting of sea ice, in a positive feedback loop. As temperatures warm, partial melting of the Greenland Ice Sheet will raise global sea levels. While no one is expecting 20 feet of sea level rise from the total melting of the Greenland Ice Sheet for many centuries, even one meter (3.3 feet) of sea level rise due to the partial melting of the Greenland Ice Sheet can cause a lot of trouble. The official word on climate, the 2007 IPCC report, predicted only a 0.6-1.9 foot sea level rise by 2100, due to melting of the Greenland ice sheet and other factors. These estimates did not include detailed models of ice flow dynamics of glaciers, on the grounds that understanding of the relevant processes was too limited for reliable model estimates. The IPCC estimates were also made before the shocking and unexpected loss of arctic sea ice of the past two summers. In light of these factors, a large number of climate scientists now believe the IPCC estimates of sea level rise this century are much too low. The most recent major paper on sea level rise, published this month by Grinsted et al., concluded that there was a "low probability" that sea level rise would be in the range forecast by the IPCC, and predicted a 0.9 - 1.3 meter (3 - 4.3 feet) rise by 2100. Pfeffer et al. last month concluded that a "most likely" range of sea level rise by 2100 is 2.6 - 6.6 feet (0.8 - 2.0 meters). Their estimates came from a detailed analysis of the processes the IPCC said were understood too poorly to model--the ice flow dynamics of glaciers in Greenland and Antarctica. The authors caution that "substantial uncertainties" exist in their estimates, and that the cost of building higher levees to protect against sea level rise is not trivial. Other recent estimates of sea level rise include 1.6 - 4.6 feet (0.5 - 1.4 meters) by Rahhmstorf (2007).
What would 3 feet of sea level rise mean?
Rising sea levels will lead to permanent and intermittent flooding in low-lying coastal areas across the world. A global sea level rise of .9 meters (3 feet) would affect 100 million people worldwide, mostly in Asia. The impact of hurricane storm surges will significantly increase as a result of sea level rise. Given a 3 foot rise in sea level, Hurricane Ike's storm surge would have overwhelmed the levees in Port Arthur, Texas, flooding the city and its important oil refineries. Galveston's sea wall would have been overtopped and possibly destroyed, allowing destruction of large portions of Galveston. Levees in New Orleans would have been overtopped, resulting in widespread flooding there, as well. I'll have a full analysis of who's at risk, and what the risks are, in a series of forthcoming blog posts this year.
What can we do?
One reasonable suggestion, presented by Trish Quinn of NOAA at the December 2008 AGU meeting, would be to limit the amount of crop residue burning that goes on in Eastern Europe and Asia each year. These fires generate large amounts of black soot that blows into the Arctic. These black particles on the white ice leads to a significant amount of warming during the summer months, when the black particles absorb sunlight.
For more information
The wunderground sea level rise page has detailed background info on sea level rise.
The wunderground Northwest Passage page is also a good reference.
realclimate.org has a nice post summarizing the recent sea level research.
I'll have a new blog post Wednesday or Thursday.
Jeff Masters
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1177
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Posted by: JeffMasters, 2:37 PM GMT on January 15, 2009
Since my last post designating arctic sea ice loss as the top climate story of 2008, I've heard a lot comments like this one: "Jeff, you just can't seem to understand the that man-made global warming is a fable and complete hoax. In all that blathering about the falsified IPCC reports and the study of the arctic ice sheet, you somehow neglected to mention that the ice recovered not only what it lost last year, but is now larger than the previous known record measured in 1978".
Well, I can understand this point of view, given complexity of the climate change issue, and the large amount of conflicting information one sees in the media. Let's look at the facts about global sea ice. You can look at the data yourself at the excellent University of Illinois Cryosphere Today web site. Reliable sea ice records go back to 1979, when satellite measurements began. Antarctic sea ice reached its greatest extent on record during the winter of 2007. Summertime ice coverage also increased in 2007-2008 compared to 2006 levels (Figure 1). However, as one can see from Figure 1, there is high variability in antarctic sea ice from winter to summer, and antarctic sea ice can best be described as having stayed constant since 1979 (as stated in the 2007 report of the Intergovernmental Panel on Climate Change (IPCC). The IPCC did find that there had been a significant decline in arctic sea ice, in all seasons, between 1979-2006. Despite this decline, there have been three periods during the past two years when the sum of the arctic and antarctic sea ice was the same or even higher than it was at the start of the satellite era (1979). An article published January 1 on Daily Tech noted that "global sea ice levels now equal those seen 29 years ago". This was pretty close to the truth on December 31, 2008, despite the fact that arctic ice was 1 million km^2 below 1979 levels, since antarctic ice was 0.5 million km^2 above 1979 levels. Although arctic sea ice extent has steadily declined since 1979, especially in summer, this decline is not as great during the winter months. One can find periods in winter when summing together antarctic and arctic sea ice area makes it appear that arctic sea ice loss is no big deal.
However, this is the wrong way to look at the issue. We don't care much about global sea ice in winter. We care about arctic sea ice in the summer. Sharp declines in summertime arctic ice are likely to cause significant and damaging alterations to Earth's climate. Cleverly quoting irrelevant facts about global wintertime sea ice data to hide the summertime loss of arctic sea ice is a tremendous disservice. It's like hiding the potential impact of a major hurricane in a one-week forecast by saying, "the average peak wind speed for the next seven days will be 17 mph", and neglecting to mention that the wind will be calm six of those days, but 120 mph on the other day. The loss of arctic sea ice the past two summers, is, in my view, the most important human-caused climate change event yet--even more significant and dangerous than the opening of the antarctic ozone hole in the 1980s. It's great that we're not seeing loss of sea ice in Antarctica. But, both the Antarctic and the Arctic can be thought of as important internal organs in our living Earth. The fact that the Antarctic has not undergone significant warming and sea ice loss in no way diminishes the urgency with which climate scientists view the diseased state of our Arctic. Fully 88 presentations on arctic sea ice were made last month at the world's largest scientific climate change conference, the American Geophysical Union (AGU) meeting in San Francisco. None of these scientists averaged together the arctic and antarctic sea ice together to show that the overall state of Earth's cryosphere was a healthy one. There was widespread concern for the health of the Arctic among all the scientists I spoke with, and none of the speakers at the talks I attended expressed the idea that the recent melting of arctic sea ice was predominantly natural, with human-caused climate change an insignificant factor. One view (Stroeve et al., 2007) is that human-emitted greenhouse gases are responsible for 47-57% of the arctic sea ice loss since 1979. Heat-absorbing black soot from fires and pollution settling on the white ice is thought to also be a significant contributor.
Figure 1. Antarctic sea ice area as observed via satellite since 1978. The maximum area in winter has ranged between 14-16 million square kilometers, about the same amount of ocean that the Arctic ice covers in winter. However, the antarctic sea ice almost entirely melts away in summer, something the Arctic sea ice does not do (yet). Antarctica is a huge continent that rises thousands of feet above the ocean. It holds about 90% of the world's fresh water, locked up in its massive ice cap. The presence of such a titanic block of ice at the bottom of the world completely dominates the weather and climate of the region, and the year-to-year fluctuations of sea ice don't have a lot of impact on temperatures there. Image credit: University of Illinois Cryosphere Today.
What is the current state of Antarctic climate?
At the December 2008 AGU meeting, scientists gave Antarctica a mixed bill of health. Isabella Velicogna of UC Irvine reported that satellite gravitational variation measurements of Antarctica's ice cap showed significant loss of ice between 2002-2008, but that the large natural variations in melting with the seasons made it difficult to be confident of the results. A somewhat different result was reported by J. Zwally of NASA. Using data from a higher-resolution satellite-borne laser altimeter, he found that there was no major loss of Antarctica's ice sheet between 2003-2007. Regardless of which data set is correct, Antarctica is in better shape than the Arctic because Antarctica has stayed relatively cool in recent decades (Figure 2). For example, the surface temperature at the South Pole cooled 0.05° C between 1980 and 1999 (Kwok and Comiso, 2002). The majority of Antarctica has shown no statistically significant warming over the past 50 years (Turner et al., 2005), and cooling has just been dominant between 1982-2004. In the period 2004-2007, much of the Antarctic warmed (Figure 3), but it is too early to say if this is the beginning of a warming trend. Check out the January 22 issue of Nature when new results about whether or not Antarctica is warming will be published.
Figure 2. Antarctic surface temperatures as observed via AHVRR satellite measurements between 1982 and 2004. Much of Antarctica cooled during this period. Image credit: IPCC The Physical Science Basis, Figure 3.32.
Figure 3. Antarctic surface temperatures as observed via AHVRR satellite measurements between 1981 and 2007. Note that the cooling trend observed from 1982-2004 reversed, thanks to warming from 2004-2007. Image credit: NASA
Why did Antarctica cool between 1982 and 2004 if there was global warming going on?
The weather of the Antarctic is dominated by a strong band of westerly winds that blow around the pole. This circumpolar vortex extends from the surface to the stratosphere, and can attain very high wind speeds, thanks to the absence of large land masses to slow it down. This vortex tends to isolate Antarctica from the rest of the globe, keeping global warming from influencing Antarctica's weather, and allowing the surface to cool. The Antarctic Peninsula, which sticks out from Antarctica towards South America, frequently lies outside the vortex. This has allowed the peninsula to warm significantly, compared to the rest of Antarctica (Figures 2 and 3). The antarctic circumpolar vortex has strengthened in the past 25-30 years, forming an even stronger barrier than usual. Tree ring records (Jones and Widman, 2004) suggest that the circumpolar vortex has shown similar strengthening in the past, so the current cooling trend in Antarctica may be natural.
Another possibility, favored by climate modelers, is that the strengthening of the circumpolar vortex and recent cooling in Antarctica are primarily due to a combination of the recent increase in greenhouse gases and the opening of the Antarctic ozone hole. The ozone hole opened up at about the same time as the recent cooling began. Ozone absorbs UV radiation which heats the atmosphere around it, so the absence of ozone has led to cooling in the stratosphere over Antarctica. This cooling has been about 10° C in October-November since 1985 (Thompson and Solomon, 2002). This has acted to intensify the circumpolar vortex, leading to surface cooling. If the climate modelers are right, the circumpolar vortex will weaken as the ozone hole diminishes in coming decades. This will allow the Antarctic to begin warming with the rest of the globe, in a decade or two.
References and resources
Intergovernmental Panel on Climate Change (IPCC), 2007, The Physical Science Basis.
Jones, J.M., and M. Widman, "Atmospheric science: Early peak in Antarctic oscillation index," Nature 432, 290-291 (18 November 2004) | doi:10.1038/432290b; Published online 17 November 2004.
Kwok, R., and J.C. Comiso, "Spatial patterns of variability in Antarctic surface temperature: Connections to the Southern Hemisphere Annular Mode and the Southern Oscillation", GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 14, 10.1029/2002GL015415, 2002.
Thompson, D.W.J., and S. Solomon, "Interpretation of Recent Southern Hemisphere Climate Change", Science 3 May 2002: Vol. 296. no. 5569, pp. 895 - 899 DOI: 10.1126/science.1069270.
Stroeve, J., M.M. Holland, W. Meier, T. Scambos, and M. Serreze, Arctic sea ice decline:Faster than forecast", GRL 34 L09501, doi:1029/2007GL029703, 2007.
Turner, J. et al., 2005, "Antarctic climate change during the last 50 years", International Journal of Climatology, Volume 25, Issue 3, pp 279-294.
Arctic sea ice
"Antarctic cooling, global warming?" RealClimate.org post, 3 December 2004.
Volunteers needed for disaster relief fund-raising
The portlight.org disaster relief charity is in the process of wrapping up its Hurricane Ike relief efforts, and is looking ahead to the future. According the new wunderground featured blog, Portlight Disaster Relief, "Our goals are to expand our network of supporters, continue to create a sense of ownership and community and create a financial reserve. Achieving these goals is critical to us being able to serve future hurricane victims in a strategic, pro-active and efficient manner." To this end, Portlight is sponsoring a fund-raising effort this March and April in 40 cities--a Spring Relief Walk. Volunteers in twenty cities have already committed to the effort, and more volunteers are needed! Check out the Portlight Disaster Relief blog for more information.
Coming Monday: Inauguration Weather. Wednesday: is the globe cooling? A report on temperatures for 2008, merely the 9th warmest year on record.
Jeff Masters
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1178