Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 19. syyskuuta 2008 klo 13:38 (GMT)
Our lull in Atlantic hurricane activity continues, and there are no signs anything will develop over the next two days. Heavy thunderstorm activity has diminished over the Lesser Antilles Islands today, and any development of this system (93L) will be slow to occur. Wind shear is marginal for development, 15-20 knots, and is forecast to remain 15-20 knots for the next five days. The NHC is giving 93L a low (<20% chance) of developing into a tropical depression by Sunday. None of the computer models develop 93L. Still, we need to keep a careful eye on this system.
The more likely place for development of the next tropical storm is off the coast of Africa. A strong tropical wave with some solid heavy thunderstorm activity is emerging from the coast today, and the GFS and NOGAPS models are predicting this system will develop into a tropical depression by early next week. Wind shear is predicted to be in the moderate range, 10-20 knots. Many of the models are also predicting development of a strong storm off the coast of North Carolina about seven days from now, but this will probably be extratropical--the season's first Nor'easter.
Arctic sea ice bottoms out at second lowest extent on record
The extent of the sea ice in the Arctic has reached its annual minimum, and is now beginning to re-freeze, according to data released by the National Snow and Ice Data Center this week. This year's minimum came on September 12, and came close to, but did not exceed, last year's record minimum set on September 16, 2007. For the second straight year, the fabled Northwest Passage explored by Roald Amundsen in 1905 opened. 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 means that for the first time in recorded history, the Arctic ice cap was an island, and one could completely circumnavigate the Arctic Ocean in ice-free waters.
Figure 1. Daily Arctic sea ice extent for September 12, 2008. The date of this year's 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 2008. Image credit: National Snow and Ice Data Center.
While it is good news that Arctic sea ice did not set a new record low, the fact that this year's decline almost matched last year's startling sea ice loss underscores the fact that the Arctic sea ice is in serious trouble. Skies were cloudier and surface air temperatures were considerably cooler (Figure 2) over the Arctic this year compared to last year, yet sea ice loss almost matched last year's record. A repeat of last year's above normal warmth and sunshine in a future summer would readily break 2007's record.
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 this summer. The biggest change is seen 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 unprecedented melting of Arctic seas ice the past two summers will have little immediate impact on the climate or on sea level rise. 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 biggest concern about Arctic sea ice loss is the warmer average temperatures it will bring to the Arctic in coming years. Instead of white, reflective ice, we will now have dark, sunlight-absorbing water at the pole, leading to a large increase in average temperature. Warmer temperatures will accelerate the melting of the Greenland ice sheet. 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 by Pfeffer et al. in the journal Science this 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.
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 godd reference.
realclimate.org has a nice post summarizing the recent sea level research.
Hurricane Ike relief
A group of wunderground members that are spearheading their own Hurricane Ike relief effort, aimed at providing assistance and supplies to people that are not in the mainstream relief areas. Donations are tax-deductible, and can be made in several ways:
Of course, contributing to the Red Cross or your local church is another great way to help out. Thanks!
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