Friday, March 31, 2006

More Warnings from a Warming World

As I reported a couple weeks ago, a slough of recent headlines, peer-reviewed journal articles and news bulletins seem to be crying out a loud and clear warning: 'The Earth is melting!' they warn us and and it's time we start listening...

Those warnings continue to roll in as five new peer-reviewed articles discussing aspects of global climate change appeared in the pages of the last two issues of Science.


Rapid Temperature Increases Above the Antarctic

The March 31st issue of Science contains a new study from scientists from the British Antarctic Survey. The study reports "an undocumented major warming of the Antarctic winter troposphere that is larger than any previously identified regional tropospheric warming on Earth" [The troposphere is the lowest layer of the atmosphere]. The study analyzes the recently digitized and "rigourously quality controlled" data from radiosonde weather balloon observations from the last 30 years and reveals that the Antarctic has the same global warming signature as that seen across the whole Earth - but three times larger than that observed globally! The data shows that Antarctic temperatures in the mid-troposphere have increased at a statistically significant rate of 0.5° to 0.7° Celsius per decade over the past 30 years.

Although scientists have been aware of rapid surface warming in the Antarctic Peninsula region for some time, this study has produced the first indications of broad-scale climate change across the whole Antarctic continent.

Dr John Turner, lead author of the study had this to say:

"The warming above the Antarctic could have implications for snowfall across the Antarctic and sea level rise. Current climate model simulations don’t reproduce the observed warming, pointing to weaknesses in their ability to represent the Antarctic climate system. Our next step is to try to improve the models."
Green Car Congress reports that daily launches of weather balloons have been carried out at many of the Antarctic research stations since the International Geophysical Year of 1957-8. The balloons carry instrument packages called radiosondes that measure temperature, humidity and winds up to heights of 20 km or more. Recently many of the old radiosonde records have been digitized and brought together in a project funded by the Scientific Committee on Antarctic Research.

The study's analysis of the radiosonde data shows a winter season warming throughout the troposphere, which extends up to about 8 km, and cooling in the stratosphere above. The largest warming of almost 0.75 º C per decade was found close to 5 km above the surface. This is more than three times the rate of warming observed for the world as a whole.

The study finds that the warming is not regionally isolated and has occurred across the whole of the Antarctic. The warming is apparent in the balloon data from Amundsen-Scott Station at the South Pole to the many stations along the coast of East Antarctica.

Although climate change at the surface of the Earth receives wide attention, the atmosphere in recent decades has in fact warmed most some 4-5 km above the surface, with the stratosphere cooling above, GCC reports. There is increasing evidence that levels of greenhouse gases have provided a blanket above the Earth trapping heat at lower levels and giving cooling in the layers above.

Air temperatures in the Antarctic Peninsula region have risen by over 2.5°C in the last 50 years, about 5 times faster than the global mean rate.


End of 21st Century Could See Highest Summer Temperatures in 130,000 Years - Sea Levels Could Rise 20 Feet

Two new studies conclude that ice sheets covering both the Arctic and Antarctic could melt more quickly this century than previous studies have predicted, a cause for concern given the potential impact of melting Antarctic and Greenland ice sheets on sea levels.

The two studies, led by scientists at the National Center for Atmospheric Research (NCAR) and the University of Arizona, blend computer modeling with paleoclimate records to show that by the year 2100, Arctic summers may be as warm as they were nearly 130,000 years ago. At that time, sea levels rose to 20 feet (6 meters) higher than they are today!

Bette Otto-Bliesner (NCAR) and Jonathan Overpeck (University of Arizona) based their findings on data from ancient coral reefs, ice cores, and other natural climate records, as well as output from the NCAR-based Community Climate System Model (CCSM), a powerful tool for simulating past, present, and future climates, according to a National Science Foundation (NSF) press release.

The NSF, which provides primary support to NCAR, funded the research. The study also involved researchers from the universities of Calgary and Colorado, the US Geological Survey, and Pennsylvania State University.

The historical data describes a period in Earth’s history characterized by a high level of Arctic warming. Based on that data, the modeling experiments Otto-Bliesner and Overpeck conducted provide important insights about possible future environmental changes in a warmer world that have the potential to significantly alter our natural and man-made environments.

Otto-Bliesner describes his work:
"Although the focus of our work is polar, the implications are global. These ice sheets have melted before and sea levels rose. The warmth needed isn’t that much more than present conditions."
The two studies show greenhouse-gas increases over the next century could warm the Arctic by 5-8 degrees Fahrenheit (3-5 degrees Celsius) in summertime. That would put Arctic temperatures about as warm as it was 130,000 years ago, between the most recent ice age and the one before it, the press release reports.

According to Dr. Shawn Marshall, University of Calgary glacialogist and second author on the papers, the difference 130,000 years ago is that the warming was caused by an increase in solar radiation over the Arctic, the result of slight changes in the Earth-Sun orbit, part of a normal cycle that occurs over tens of thousands of years. “This time around the warming is man-made, caused by carbon dioxide emissions, but the effects on Arctic sea ice, permafrost, and icefields are forecast to be similar," Dr. Marshall writes.

Although simulation results depend on the assumptions and conditions of different models, estimates of warming from the CCSM are within the range projected by other climate models, according to the authors.

"Getting the past climate change correct in these models gives us more confidence in their ability to predict future climate change," says Otto-Bliesner.

The CCSM suggests that during the interglacial period, melt water from Greenland and other Arctic sources raised sea level by as much as 11 feet (3.5 meters), Otto-Bliesner says. However, coral records indicate the sea level actually rose 13-20 feet (4-6 meters) or more. Overpeck thus concludes that Antarctic melting must have produced the remainder of the sea-level rise.

These studies are the first to link Arctic and Antarctic melting in the last interglacial period. Marine diatoms and beryllium isotopes found beneath the West Antarctic Ice Sheet indicate parts of the ice disappeared at some point over the past several hundred thousand years.

Overpeck theorizes that the rise in sea levels produced by Arctic warming and melting could have helped destabilize ice shelves at the edge of the Antarctic ice sheet, leading to their collapse. If such a process occurred today, it would be accelerated by global-scale greenhouse-induced warming year round, Overpeck says. In the Arctic, melting would likely be hastened by pollution that darkens snow and enables it to absorb more sunlight.

The two papers appear in the March 24th issue of Science.


Warming Ocean Waters are Melting Ice Worldwide

According to an article by Robert Bindschadler, a glaciologist at NASA’s Goddard Space Flight Center, the pieces to a years-old scientific puzzle have come together to confirm warmer water temperatures are creeping into the Earth's colder areas. Those warm waters are increasing melting and accelerating ice flow in polar areas.

Temperatures collected from ships and buoys showed a warming of all oceans, according to a NASA article. That increase began before satellite sensors detected temperature increases of sea surfaces. Most of the warming was limited to the oceans’ upper 1,000 meters (.62 mile), except in the North Atlantic. In the cold North Atlantic waters, heat penetrated even deeper, the study found. This warming has increased the melting of sea ice in the North Atlantic.

These warm waters are having another effect, which may potentially be of great significance to sea level rise. The study finds that the warming waters are beginning to melt the undersides of the floating fringes of the Greenland ice sheet, even at great depths. It is these fringes that have been holding back vast stores of ice locked up in the Greenland ice sheet, and as this ice has been melting, the glaciers have hastened their flow to the sea.

A recent assessment in the changes in speed and the amount of snow and ice around Greenland confirms a large melting of outflow glaciers and acceleration of ice flow, NASA reports. Three large glaciers, the Kangerdlugssuaq, Helheim and Jakobshavns Isbrae have been melting at a rapid rate over the past several years.

[Image: Jakobshavn Glacier Retreat 2001-2003: Jakobshavn Isbrae holds the record as Greenland's fastest moving glacier and major contributor to the mass balance of the continental ice sheet. Starting in late 2000, following a period of slowing down in the mid 1990s, the glacier showed significant acceleration and nearly doubled its discharge of ice. The following image from the Landsat satellite shows the retreat of Jakobshavn's calving front from 2001 to 2003. Credit: NASA]

Jakobshavns, the largest outlet glacier on Greenland's east coast, has been annually thinning at 15 meters (49.2 feet) since 1997. The other two glaciers have also been thinning. Kangerdlugssuaq at 40 meters (131.2 feet) per year and Helheim at 25 meters per year (82.0 feet), which can't be explained by normal melting. All of these glaciers have also been accelerating. This isn’t just happening in Greenland, scientists are seeing similar behavior in Antarctica as well.

"Deep outlet glaciers around both major ice sheets are accelerating and thinning means warm water has reached them," Bindschadler said. "I see no process to reverse this and expect increased ice sheet discharge to continue and probably to spread with the result being further accelerations to sea level rise."

Some climatologists argue that increased snowfall in a warming Arctic climate will balance out the ice lost through outlet glaciers. Bindschadler concludes, however, that the evidence is clear that increased snowfall predicted in a warmer climate can't possibly keep up with the increased rate of discharge his study finds.

While Bindschadler's article is opinion, it fits previously disconnected pieces of the climate and ice puzzle together and attempts to draw conclusions. The conclusions cannot be verified without new measurements, and NASA is compiling them with satellites like ICESat, NASA reports. ICESat enables scientists to precisely measure changes in the elevation of ice and snow on glaciers and ice sheets as they respond to a changing climate.

Bindschadler's article also appears is in the March 24 issue of Science magazine.


Global Warming Can Cause 'Glacial Earthquakes' in Polar Areas

In the last of these five papers, a team from Harvard University and Columbia University report an unexpected offshoot of global warming: “glacial earthquakes” in which Manhattan-sized glaciers lurch unexpectedly, yielding temblors up to magnitude 5.1 on the moment-magnitude scale, which is similar to the Richter scale, a Harvard Gazette article reports.

Glacial earthquakes in Greenland, the researchers found, are most common in July and August, and have more than doubled in number since 2002.

Scientists Göran Ekström and Victor C. Tsai at Harvard and Meredith Nettles at Columbia report on Greenland's glacial earthquakes in a paper which also appears in the March 24th issue of the journal Science.

"People often think of glaciers as inert and slow-moving, but in fact they can also move rather quickly," Ekström says. "Some of Greenland’s glaciers, as large as Manhattan and as tall as the Empire State Building, can move 10 meters in less than a minute, a jolt that is sufficient to generate moderate seismic waves."

According to the Gazette, as glaciers and the snow atop them gradually melt, water seeps downward. When enough water accumulates at a glacier's base, it can serve as a lubricant, causing blocks of ice some 10 cubic kilometers in size to lurch down valleys known as 'outlet glaciers,' which funnel all of Greenland's glacial runoff toward the surrounding sea.

"Our results suggest that these major outlet glaciers can respond to changes in climate conditions much more quickly than we had thought," says Nettles, a postdoctoral researcher at Columbia's Lamont-Doherty Earth Observatory. "Greenland's glaciers deliver large quantities of fresh water to the oceans, so the implications for climate change are serious. We believe that further warming of the climate is likely to accelerate the behavior we've documented."

Although Greenland is not a hotbed of traditional seismic activity associated with the grinding of the Earth's tectonic plates, seismometers worldwide detected 182 earthquakes there between January 1993 and October 2005, the Gazette writes. Ekström, Nettles, and Tsai examined the 136 best-documented of these seismic events, ranging in magnitude from 4.6 to 5.1. The researchers found that all 136 temblors originated at major valleys draining the Greenland Ice Sheet, implicating glacial activity in the seismic disturbances.

Of the 136 earthquakes analyzed, more than a third occurred during the months of July (22 earthquakes) and August (24 earthquakes). By comparison, January and February each saw a total of only four earthquakes between 1993 and 2005. Nonglacial earthquakes in polar regions show no seasonal variability.

Greenland's overall number of glacial earthquakes also increased markedly between 1993 and 2005, the study found. Annual totals hovered between six and 15 through 2002, followed by sharp increases to 20 earthquakes in 2003, 24 in 2004, and 32 in the first 10 months of 2005. A single area of northwestern Greenland, where only one seismic episode was observed between 1993 and 1999, experienced more than two dozen glacial quakes between 2000 and 2005, for example. Polar regions have not experienced increases in nonglacial earthquakes in recent years.

While glacial earthquakes appear most common in Greenland, Ekström, Nettles, and Tsai have also found evidence of glacial earthquakes originating at mountain glaciers in Alaska and at glaciers located in ice streams along the edges of Antarctica.

Ekström, Nettles, and Tsai's work was funded by the National Science Foundation.


Resources:

  • Significant warming of the Antarctic winter troposphere”; J. Turner, T. A. Lachlan-Cope, S. Colwell, G. J. Marshall, W. M. Connolley; Science 31 March 2006: Vol. 311. no. 5769, pp. 1914 - 1917; DOI:10.1126/science.1121652

  • Paleoclimatic Evidence for Future Ice-Sheet Instability and Rapid Sea-Level Rise,”; Jonathan T. Overpeck, Bette L. Otto-Bliesner, Gifford H. Miller,Daniel R. Muhs, Richard B. Alley, Jeffrey T. Kiehl; Science 24 March 2006:Vol. 311. no. 5768, pp. 1747–1750; DOI: 10.1126/science.1115159

  • Simulating Arctic Climate Warmth and Icefield Retreat in the Last Interglaciation,”; Bette L. Otto-Bliesner, Shawn J. Marshall, Jonathan T. Overpeck, Gifford H. Miller, Aixue Hu; Science 24 March 2006:Vol. 311. no. 5768, pp. 1751–1753; DOI: 10.1126/science.1120808

  • Hitting the Ice Sheets Where It Hurts”; Robert Bindschadler; Science 24 March 2006:Vol. 311. no. 5768, pp. 1720–1721; DOI:10.1126/science.1125226

  • Seasonality and Increasing Frequency of Greenland Glacial Earthquakes”; Göran Ekström, Meredith Nettles, Victor C. Tsai, Science 24 March 2006:Vol. 311. no. 5768, pp. 1756–1758; DOI: 10.1126/science.1122112


  • [A hat tip to Green Car Congress]

    1 comment:

    Heiko said...

    Have a look at real climate, they discuss a number of these papers.

    The reporting in the popular press is somewhat misleading. For example, they don't mention that for most of Antarctica there's only been minor surface warming.

    They also fail to mention that we don't expect 6 meter sea level rise by 2100 and that the paper doesn't claim that either.

    Real climate's summary includes the following sentence:
    "the new results do not require us to revise projections of sea level rise over the next century or so"
    To balance that they also say:
    "none of the new evidence points in the direction of smaller rates of sea level rise in the future, and probably nudge us closer to the upper end of the IPCC predictions."