Melting Greenland ice sheets may threaten Northeast United States, Canada
May 27, 2009
This visualization, based on new computer modeling, shows that sea level rise may be an additional 10 centimeters (4 inches) higher by populated areas in northeastern North America than previously thought. Extreme northeastern North America and Greenland may experience even higher sea level rise. (Graphic courtesy Geophysical Research Letters, modified by UCAR.)
Melting of the Greenland ice sheet this century may drive more water than previously thought toward the already threatened coastlines of New York, Boston, Halifax, and other cities in the northeastern United States and in Canada, according to new research led by the National Center for Atmospheric Research (NCAR).
The study, which will be published Friday in Geophysical Research Letters, finds that if Greenland's ice melts at moderate to high rates, ocean circulation by 2100 may shift and cause sea levels off the northeast coast of North America to rise by about 12 to 20 inches (about 30 to 50 centimeters) more than in other coastal areas. The research builds on recent reports that have found that sea level rise associated with global warming could adversely affect North America, and its findings suggest that the situation is more threatening than previously believed.
"If the Greenland melt continues to accelerate, we could see significant impacts this century on the northeast U.S. coast from the resulting sea level rise," says NCAR scientist Aixue Hu, the lead author. "Major northeastern cities are directly in the path of the greatest rise."
A study in Nature Geoscience in March warned that warmer water temperatures could shift ocean currents in a way that would raise sea levels off the Northeast by about 8 inches (20 cm) more than the average global sea level rise. But it did not include the additional impact of Greenland's ice, which at moderate to high melt rates would further accelerate changes in ocean circulation and drive an additional 4 to 12 inches (about 10 to 30 cm) of water toward heavily populated areas in northeastern North America on top of average global sea level rise. More remote areas in extreme northeastern Canada and Greenland could see even higher sea level rise.
Scientists have been cautious about estimating average sea level rise this century in part because of complex processes within ice sheets. The 2007 assessment of the Intergovernmental Panel on Climate Change projected that sea levels worldwide could rise by an average of 7 to 23 inches (18 to 59 cm) this century, but many researchers believe the rise will be greater because of dynamic factors in ice sheets that appear to have accelerated the melting rate in recent years.
The new research was funded by the U.S. Department of Energy and by NCAR's sponsor, the National Science Foundation. It was conducted by scientists at NCAR, the University of Colorado at Boulder, and Florida State University.
How much meltwater?
To assess the impact of Greenland ice melt on ocean circulation, Hu and his coauthors used the Community Climate System Model, an NCAR-based computer model that simulates global climate. They considered three scenarios: the melt rate continuing to increase by 7 percent per year, as has been the case in recent years, or the melt rate slowing down to an increase of either 1 or 3 percent per year.
If Greenland's melt rate slows down to a 3 percent annual increase, the study team's computer simulations indicate that the runoff from its ice sheet could alter ocean circulation in a way that would direct about a foot of water toward the northeast coast of North America by 2100. This would be on top of the average global sea level rise expected as a result of global warming. Although the study team did not try to estimate that mean global sea level rise, their simulations indicated that melt from Greenland alone under the 3 percent scenario could raise worldwide sea levels by an average of 21 inches (54 cm).
If the annual increase in the melt rate dropped to 1 percent, the runoff would not raise northeastern sea levels by more than the 8 inches (20 cm) found in the earlier study in Nature Geoscience. But if the melt rate continued at its present 7 percent increase per year through 2050 and then leveled off, the study suggests that the northeast coast could see as much as 20 inches (50 cm) of sea level rise above a global average that could be several feet. However, Hu cautioned that other modeling studies have indicated that the 7 percent scenario is unlikely.
In addition to sea level rise, Hu and his co-authors found that if the Greenland melt rate were to defy expectations and continue its 7 percent increase, this would drain enough fresh water into the North Atlantic to weaken the oceanic circulation that pumps warm water to the Arctic. Ironically, this weakening of the meridional overturning circulation would help the Arctic avoid some of the impacts of global warming and lead to at least the temporary recovery of Arctic sea ice by the end of the century.
Why the Northeast?
The northeast coast of North America is especially vulnerable to the effects of Greenland ice melt because of the way the meridional overturning circulation acts like a conveyer belt transporting water through the Atlantic Ocean. The circulation carries warm Atlantic water from the tropics to the north, where it cools and descends to create a dense layer of cold water. As a result, sea level is currently about 28 inches (71 cm) lower in the North Atlantic than the North Pacific, which lacks such a dense layer.
If the melting of the Greenland Ice Sheet were to increase by 3 percent or 7 percent yearly, the additional fresh water could partially disrupt the northward conveyor belt. This would reduce the accumulation of deep, dense water. Instead, the deep water would be slightly warmer, expanding and elevating the surface across portions of the North Atlantic.
Unlike water in a bathtub, water in the oceans does not spread out evenly. Sea level can vary by several feet from one region to another, depending on such factors as ocean circulation and the extent to which water at lower depths is compressed.
"The oceans will not rise uniformly as the world warms," says NCAR scientist Gerald Meehl, a co-author of the paper. "Ocean dynamics will push water in certain directions, so some locations will experience sea level rise that is larger than the global average."
Source: National Center for Atmospheric Research
Mar 13, 2009 |
not rated yet |
0
http://deepseanew...sidered/
Could this impact the "consensus" (stifle laugh here) on which the Even More Dire predictions in this paper is modeled?
The AGW Loop
IF empirical_data contradicts model
AND fewer_people believe Dire_Predictions
THEN
Increment Dire_Predictions
Increment Hysterical_Tone
Loop
LOL!
For the umpteenth time, it is not the CO2 that is causing the melt. CO2 levels were much lower 1,000 years ago but the shores and coastlands of Greenland really were green during those times and the global weather was hotter by about 5°C.
As I said above. Dairy farms in Greenland in 1000AD. Yet 200 years later Iceland was surrounded by ice all year long.
Global warming? Global horsesh!t is more likely.
Freeman Dyson. Anyone here at all familiar with Freeman Dyson? Now that Feynman is dead, Dyson may well be the smartest man in the world. Dyson opines that water vapor is several orders of magnitude greater in its greenhouse effect . . . so much stronger than CO2 as to reduce CO2's impact into background noise, so far as the global climate is concerned.
Case closed.
And this has happened before when the Northwest passage opened up in the 1930s.
The interesting thing is that the last 2 winters have seen more ice accumulate than predicted. It threw the Germans for a loop when they flew over the arctic with their electromagnetic induction probe:
http://wattsupwit...sdicken/
You are right about water vapor being a more potent green house gas than carbon dioxide. However, that completely misses the point. What follows is a technical description of heat transfer, not agreement with or argument against AGW.
To better understand why carbon dioxide is important, you have to look at the absorption lines for each of the molecules (water vapor and CO2). There are about a hundred of thousand cataloged lines for each asymmetric molecule that is sensitive to bending or rotation. Water vapor has a broad strong absorption spectra (made up of thousands of lines) in the infrared (which is what keeps the earth habitable). These lines come about by the quantum mechanical absorption of a photon of a specific wavelength causing bending and/or rotation in the molecule. However, there are holes in the water vapor absorption spectra (as there are in all gas spectra). If there were not, then the trace gases would not make a difference. Since there are holes in the spectra it becomes important to understand which molecules have absorption lines in those holes. The most important molecules that do are CO2 and CH4.
The bottom line is that CO2 absorption is relatively independent of H2O because the lines do not overlap in some important areas (or are much stronger for CO2 at a specific line than for H2O). Don't misunderstand, there are overlaps in many areas and there are complicating issues like line broadening that enhance overlap. However, water vapor is not 100% effective in absorbing infrared in the range the earth radiates at. CO2, CH4, and other gases are also not 100% effective. Instead, the trace gases pick up a bit of the energy that H2O misses. Those lines that are picking up missed energy are what makes CO2 and CH4 important even though H2O is the clearly stronger absorber. If you do not understand this very important issue then you need to get a good book on radiative heat transfer. I recommend "Thermal Radiation Heat Transfer" by Siegel and Howell.
How about factoring in the elevation of most of the ice in Greenland. Most is so high that no matter how hot the lowlands get the temperature drop through altitude would stop the ice melting and considerably slow it down at moderate elevations. Same for Antarctica.
http://noconsensu...ore-3943
Let's talk satellite images:
If the atmosphere was capturing more heat due to increased CO2 there would be a visible hot spot at the tropopause, most notably where the Ozone is thinnest. This is one of the predictive aspects of the AGW hypothesis. Problem is, there's no hot spot. There isn't even really a deviation outside of instrumental variation.
Dagman,
You have almost made it to the real world, finish the process and join us my friend!!
The problem, you see, is that the speculators (theorists, if you prefer) continue to deny all the real world evidence that falsifies their man-made GW theories.
That's why it's all crap!!!!!!!!!!