|Figure 2. The graph above shows daily Arctic sea ice extent as of July 5, 2010. The solid light blue line indicates 2010; dashed green shows 2007; solid pink shows 2006, and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.|
—Credit: National Snow and Ice Data Center
Weather conditions, atmospheric patterns, and cloud cover over the next month will play a major role in determining whether the 2010 sea ice decline tracks at a level similar to 2007, or more like 2006. Although ice extent was greater in June 2007 than June 2006, in July 2007 the ice loss rate accelerated. That fast decline led up to the record low ice extent of September 2007. 雖然2007年六月海冰面積比2006年六月還要大，但2007年到了七月海冰加速消融，創下2007年九月歷史最低海冰面積記錄。
However, it would not be surprising to see the rate of ice loss slow in coming weeks as the melt process starts to encounter thicker, second and third year ice in the central Arctic Ocean. Loss of ice has already slowed in the Beaufort and Chukchi Seas due to the tongue of thicker, older ice in the region noted in our April update.
June 2010 compared to past years
|Figure 3. Monthly June ice extent for 1979 to 2010 shows a decline of 3.5% per decade. |
—Credit: National Snow and Ice Data Center
The linear rate of monthly decline for June over the 1979 to 2010 period is now 3.5% per decade. 1979-2010期六月的月降速率線，每十年降3.5%。This year’s daily June rate of decline was the fastest in the satellite record; the previous record for the fastest rate of June decline was set in 1999. This rapid decline was in part driven by ice loss in Hudson Bay.
The Arctic dipole anomaly
The record low ice extent of September 2007 was influenced by a persistent atmospheric pressure pattern called the summer Arctic dipole anomaly (DA). The DA features unusually high pressure centered over the northern Beaufort Sea and unusually low pressure centered over the Kara Sea, along the Eurasian coast. In accord with Buys Ballot's Law, this pattern causes winds to blow from the south along the Siberian coast, helping to push ice away from the coast and favoring strong melt. The DA pattern also promotes northerly winds in the Fram Strait region, helping to flush ice out of the Arctic Ocean into the North Atlantic. The DA pattern may also favor the import of warm ocean waters from the North Pacific that hastens ice melt.
June 2010 saw the return of the DA, but with the pressure centers shifted slightly compared to summer 2007. As a result, winds along the Siberian coastal sector are blowing more from the east rather than from the south. Whether or not the DA pattern persists through the rest of summer will bear strongly on whether a new record low in ice extent is set in September 2010.
|Figure 5. This satellite image, acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the NASA Terra satellite on June 30, 2010, shows that Nares Strait was open and sea ice was flowing through it. Normally Nares Strait remains plugged by an "ice arch" through early July, but this year it was clear by May.|
—Credit: National Snow and Ice Data Center courtesy NASA/GSFC MODIS Rapid Response
Ron Kwok of the Jet Propulsion Laboratory (JPL) reports that Nares Strait, the narrow passageway between northwest Greenland and Ellesmere Island is clear of the ice “arch" that usually plugs southward transport of the old, thick ice in the Lincoln Sea. Typically the ice arch forms in winter and breaks up in early July. This year the arch formed around March 15th and lasted only 56 days, breaking up in May.
In 2007 the ice arch did not form at all, allowing twice as much export through Nares Strait than the annual mean. Although the export of sea ice out of the Arctic Ocean through Nares Strait is very small in comparison to the export through Fram Strait, the Lincoln Sea contains some of the Arctic’s thickest ice. For the ice flux rates out of Nares strait, see Figure 5a.
Meanwhile, in Antarctica
|Figure 6. The graph above shows daily Antarctic sea ice extent as of July 5, 2010. The solid light blue line indicates 2010; dashed green shows 2007, and solid gray indicates average extent from 1979 to 2000. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.|
—Credit: National Snow and Ice Data Center
At the end of June, Southern Hemisphere mid-winter, the sea ice surrounding Antarctica was more than two standard deviations greater than normal. On June 30, Antarctic sea ice extent was15.88 million square kilometers (6.13 million square miles), compared to the 1979 to 2000 average of 14.64 million square kilometers (5.65 million square miles) for that day. ps:現在南半球是冬季！
While recent studies have shown that wintertime Antarctic sea ice has a weak upward trend, and substantial variability both within a year and from year to year, the differences between Arctic and Antarctic sea ice trends are not unexpected. Climate models consistently project that the Arctic will warm more quickly than the Antarctic, largely due to the strong climate feedbacks in the Arctic. 氣候反饋北極比南極更強烈，所以北極比南極更快暖化。
Warming is amplified by the loss of ice cover in the Arctic Ocean in areas that had been ice-covered for decades, and by the warming of Arctic lands as snow cover is lost earlier and returns later than in recent decades.
Moreover, rising levels of greenhouse gases and the loss of stratospheric ozone appear to be affecting wind patterns around Antarctica. Shifts in this circulation are referred to as the Antarctic Oscillation (AAO). As greenhouse gases have increased, and especially when ozone is lost in spring, there is a tendency for these winds to strengthen (a positive AAO index). The net effect is to push sea ice eastward, and northward, increasing the ice extent. As the current sea ice anomaly has developed, the AAO index has been strongly positive. See the NOAA AAO Index Web site. For more information about the differences between sea ice dynamics in the Arctic and Antarctic, see the NSIDC All About Sea Ice Web site.
For previous analyses, please see the drop-down menu under Archives in the right navigation at the top of this page.
NSIDC scientists provide Arctic Sea Ice News & Analysis, with partial support from NASA.
2010/07/1 AFP 鄭竹雅 譯
馬洛瑞在聖母峰長征之旅身亡，他死前目睹壯觀、雪白的S型廣袤冰河， 如今這條「絨布冰川」（MainRongbuk Glacier）已大幅萎縮。一座座結凍的冰峰還在，但變小也變矮，成為細窄的線狀。過去這些冰峰的體積足以媲美辦公大樓。
布里薛斯詳加比較今昔照片，確定絨布冰川的深度降低97公尺。他14日於紐約亞洲協會 （Asia Society）說：「此區和喜馬拉雅山脈中、西段的融化速度非常快，令人震驚。」該協會本月13日至8月15日展示這些照片。在全球暖化的原因和真相引發政治激辯之際，布里薛斯的說法相當實際。他沿著早期3位偉大登山攝影家的步伐前進，包括馬洛瑞、出生於加拿大的測繪先驅惠勒（Edward Wheeler），以及作品橫跨19與20世紀的義大利攝影師塞拉（Vittorio Sella）。
卡爾蒂蘇格杜布島(Carti Sugdub)領袖普雷西亞多記得，在他孩提時代，淹水情況罕見、短暫，且水位不會太高。他說：“現在完全不是那麼回事了。現在可嚴重了。” 在普雷西亞多的64歲生涯裡，積水深度上漲了幾英寸，這與全球海平面的上升是一致的。島民們開採珊瑚，減少了對海浪的緩衝作用，使這一問題加劇。
巴拿馬政府說，包括卡爾蒂蘇格杜布島在內的一些位於巴拿馬東北部海岸的小島，都受氣候暖化影響，以致半自治的3萬2000個庫納(Kuna)族 人，近半數的生計受到影響。卡爾蒂蘇格杜布島的2000個島民計畫搬遷到巴拿馬本土的庫納族自治區的沿海地區居住。他們看中的是距離海灘大約半小時腳程的一片山地。 帶領島民砍倒熱帶森林，以便為建造新定居點鋪路的普雷西亞多說：“海平面在上升，搬遷迫在眉睫。” 巴拿馬史密森尼熱帶研究所的海洋生物學家和珊瑚專家古茨曼說：“這已不只是科學家說氣候變化和海平面上升將引發洪水和影響一些人了……這已在真實世界裡出現。”
Greenland Glacier Retreats One Mile Overnight! NASA Shows Satellite Photos
by Matthew McDermott, New York, NY on 07.12.10
Thomas Wagner, cryospheric program scientist at NASA, commented:
While there have been ice breakouts of this magnitude from Jakobshavn and other glaciers in the past, this event is unusual because it occurs on the heels of a warm winter that saw no sea ice in the surrounding bay. While this exact relationship between these events is being determined, it lends credence to the theory that warming of the oceans is responsible for the ice loss observed throughout Greenland and Antarctica.
The Jakobshavn glacier is located on the west coast of Greenland and has retreated more than 45 kilometers (27 miles) in the past 160 years, including 10 kilometers in the past decade alone. Estimates show that about 10% of all ice lost in Greenland comes through Jakobshavn--making it the single largest contributor to sea level rise in the northern hemisphere.
Sea Levels Rising in Parts of Indian Ocean; Greenhouse Gases Play Role, Study Finds
ScienceDaily (July 13, 2010) — Newly detected rising sea levels in parts of the Indian Ocean, including the coastlines of the Bay of Bengal, the Arabian Sea, Sri Lanka, Sumatra and Java, appear to be at least partly a result of human-induced increases of atmospheric greenhouse gases, says a study led by the University of Colorado at Boulder. 最新偵測部分印度洋上升中海平面，偵測範圍包括孟加拉灣、阿拉伯海、斯里蘭卡、蘇門答臘、爪哇沿線海岸，顯示至少部份是人類引起大氣層溫室氣體增加的結果，美國科羅拉多大學博爾德分校研究顯示。
|Indian Ocean, from Visible Earth (http://visibleearth.nasa.gov). (Credit: Reto Stockli, NASA Earth Observatory)|
The key player in the process is the Indo-Pacific warm pool, an enormous, bathtub-shaped area of the tropical oceans stretching from the east coast of Africa west to the International Date Line in the Pacific. The warm pool has heated by about 1 degree Fahrenheit, or 0.5 degrees Celsius, in the past 50 years, primarily caused by human-generated increases of greenhouse gases, said Han. 印度洋暖化池過去50年間大約上升華氏１度(或攝氏0,5度)，主要由人為增加溫室氣體所造成。
"Our results from this study imply that if future anthropogenic warming effects in the Indo-Pacific warm pool dominate natural variability, mid-ocean islands such as the Mascarenhas Archipelago, coasts of Indonesia, Sumatra and the north Indian Ocean may experience significantly more sea level rise than the global average," said Han of CU-Boulder's atmospheric and oceanic sciences department. 我們研究結果說明了如果未來「人為暖化」效應發生在印度洋暖化池區域天然條件，像一些島嶼．．將經歷比全球平均值更嚴重的海平面上升。
A paper on the subject was published in Nature Geoscience. Co-authors included Balaji Rajagopalan, Xiao-Wei Quan, Jih-wang Wang and Laurie Trenary of CU-Boulder, Gerald Meehl, John Fasullo, Aixue Hu, William Large and Stephen Yeager of the National Center for Atmospheric Research in Boulder, Jialin Lin of Ohio State University, and Alan Walcraft and Toshiaki Shinoda of the Naval Research Laboratory in Mississippi. While a number of areas in the Indian Ocean region are showing sea level rise, the study also indicated the Seychelles Islands and Zanzibar off Tanzania's coastline show the largest sea level drop. Global sea level patterns are not geographically uniform, and sea rise in some areas correlate with sea level fall in other areas, said NCAR's Meehl. 全球海平面上升並非單一地理形式，某些區域海洋上升與另一區域海平面下降有關聯。
The Indian Ocean is the world's third largest ocean and makes up about 20 percent of the water on Earth's surface. The ocean is bounded on the west by East Africa, on the north by India, on the east by Indochina and Australia, and on the south by the Southern Ocean off the coast of Antarctica. The patterns of sea level change are driven by the combined enhancement of two primary atmospheric wind patterns known as the Hadley circulation and the Walker circulation. The Hadley circulation in the Indian Ocean is dominated by air currents rising above strongly heated tropical waters near the equator and flowing poleward, then sinking to the ocean in the subtropics and causing surface air to flow back toward the equator.
The Indian Ocean's Walker circulation causes air to rise and flow westward at upper levels, sink to the surface and then flow eastward back toward the Indo-Pacific warm pool. "The combined enhancement of the Hadley and Walker circulation form a distinct surface wind pattern that drives specific sea level patterns," said Han. The international research team used several different sophisticated ocean and climate models for the study, including the Parallel Ocean Program -- the ocean component of NCAR's widely used Community Climate System Model. In addition, the team used a wind-driven, linear ocean model for the study.
"Our new results show that human-caused changes of atmospheric and oceanic circulation over the Indian Ocean region -- which have not been studied previously -- are the major cause for the regional variability of sea level change," wrote the authors in Nature Geoscience.
Han said that based on all-season data records, there is no significant sea level rise around the Maldives. But when the team looked at winter season data only, the Maldives show significant sea level rise, a cause for concern. The smallest Asian country, the Maldives is made up of more than 1,000 islands -- about 200 of which are inhabited by about 300,000 people -- and are on average only about five feet above sea level. The complex circulation patterns in the Indian Ocean may also affect precipitation by forcing even more atmospheric air down to the surface in Indian Ocean subtropical regions than normal, Han speculated. "This may favor a weakening of atmospheric convection in the subtropics, which may increase rainfall in the eastern tropical regions of the Indian Ocean and increase drought in the western equatorial Indian Ocean region, including east Africa," Han said.
The new study indicates that in order to document sea level change on a global scale, researchers also need to know the specifics of regional sea level changes that will be important for coastal and island regions, said NCAR's Hu. Along the coasts of the northern Indian Ocean, seas have risen by an average of about 0.5 inches, or 13 millimeters, per decade. "It is important for us to understand the regional changes of the sea level, which will have effects on coastal and island regions," said Hu. The study was funded by a number of organizations, including NCAR, the National Science Foundation, NASA and the U.S. Department of Energy.
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Colorado at Boulder, via EurekAlert!, a service of AAAS.