Why Arctic sea ice is shrinking

By: Dr. Jeff Masters , 10:25 PM GMT on February 20, 2007

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Second of three vacation blogs from Dr. Masters. Enjoy.

Since 1979, coverage of Arctic sea ice has shrunk by about 10% in winter and 20% in summer. The vertical thickness of the ice has also shrunk. According to the "official" Intergovernmental Panel on Climate Change (IPCC) report in 2001, Arctic sea ice decreased in thickness by about 40% between 1958 and 1997. This figure came from submarine sonar measurements taken over five cruises in the autumns of 1958, 1960, 1962, 1970, and 1976 when compared with three cruises in the autumns of 1993, 1996, and 1997 (Rothrock et. al, 1999). However, according to modeling studies by Holloway and Sou (2001), these results are highly uncertain, since not all years or locations in the Arctic were sampled. They found that if the first five cruises had been done just one year earlier (September 1957, 1959, 1961, 1969, 1975) and the three latter cruises had been done one year later (September 1994, 1997, 1998), the sonar measurements would have shown only an 11%-15% decrease in thickness. Arctic sea ice varies greatly in thickness, and currents and winds are always pushing the ice around, making it difficult to measure how the average thickness has been declining.

Warmer air and water temperatures have contributed to the sea ice decline

Annual average surface temperature has increased about 1 degree C since 1980 over the Arctic, which accounts for much of the sea ice melt. In addition, some melting has occurred from beneath the ice, due to warmer ocean waters. Global warming has heated up both the North Pacific and North Atlantic waters significantly over the past 30 years. Warmer waters have been brought into the Arctic Ocean from the Pacific via an ocean current flowing through the Bering Strait between Alaska and Russia, and from the Atlantic via an ocean current flowing northwards along the European coast.



Figure 1. The Arctic Oscillation (AO) index from 1899 - 2006. The AO is a measure of the difference in surface pressure between the north pole and about 45 degrees north latitude. Image credit: Dave Thompson of Colorado State University.

Wind patterns are a major cause of sea ice loss


The Arctic Oscillation is an observed natural pattern of surface pressure variations in the Northern Hemisphere. The "positive index" of the AO is defined when the surface pressure is below normal at the north pole and above normal at about 45 degrees north latitude. Positive Arctic Oscillation conditions steer storms farther north, bringing stronger surface westerly winds in the North Atlantic and warmer and wetter than normal conditions to the Arctic and northern Europe. The winds and ocean currents during the positive Arctic Oscillation mode tend to drive sea ice from west to east along the north shore of Canada, then out of the Arctic Ocean through the channel of water to the east of Greenland (Fram Strait).

When one looks at the wintertime pattern of the Arctic Oscillation (AO) over the past 100 years, a mostly random pattern of positive and negative AO modes is apparent (Figure 1). However, one anomalous period is very striking: a string of seven consecutive years with a positive AO, including two years (1989 and 1990) with the highest AO index ever observed. During this period, strong westerly winds rapidly flushed more than 80% of the oldest, thickest sea ice out of the Arctic Ocean, leaving most of the Arctic covered with ice less than three years old (Figure 2). Younger ice is much thinner, and melts much more readily. Rigor and Wallace (2004) estimate that at least half of the loss of sea ice in the Arctic since 1979 is due to these six years of strange weather with very low surface pressure over the Arctic. Did climate change cause this unusual pattern between 1989 and 1995? It is possible, but no one has published any papers showing how this might have occurred. For now, the assumption is that this major loss of Arctic sea ice due to wind patterns between 1989-1995 is natural.

The big concern is that since the strange positive Arctic Oscillation years of 1989-1995, a number of years with negative AO have occurred. Normally, during negative AO years, ice extent and thickness increase in the Arctic. But instead, ice extent and thickness during 2002-2006 have shown an unprecedented series of record minima, giving rise to fears that we are on our way to an ice-free Arctic later this century.



Figure 2. The change in age and thickness of sea ice between 1987 and 2005. In 1987, most of the Arctic sea ice was old and thick, generally more than ten years old. A period of strong positive Arctic Oscillation conditions between 1989 and 1995 created winds and currents that flushed most of this old ice out of the Arctic Ocean, through Fram Strait to the east of Greenland. The new ice that replaced the old ice is much thinner. Image credit: Rigor, I. G., and J. M. Wallace (2004), "Variations in the age of Arctic sea-ice and summer sea-ice extent," Geophys. Res. Lett., 31, L09401, doi:10.1029/2004GL019492.


This is the third in a series of five blogs on climate change in the Arctic that will appear every Monday and Thursday over the next two weeks. Next blog: Future abrupt loss of Arctic sea ice.

Also, be sure to visit our new Climate Change blog, written by Dr. Ricky Rood of the University of Michigan.

Jeff Masters

References
Holloway, G. and T. Sou, 2001, "Has Arctic Sea Ice Rapidly Thinned?", Journal of Climate 15, p1691-1701, 2001.

Rigor, I. G., and J. M. Wallace (2004), "Variations in the age of Arctic sea-ice and summer sea-ice extent," Geophys. Res. Lett., 31, L09401, doi:10.1029/2004GL019492.

Rothrock D.A., Y. Yu, and G.A. Maykut, 1999: "Thinning of the Arctic sea ice cover." Geophys. Res. Lett., 26, 3469-3472.

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142. Skyepony (Mod)
2:57 PM GMT on February 22, 2007
Cyclone hits flooded Mozambique

Cat 4 worst to hit the area in recorded history.
Member Since: August 10, 2005 Posts: 224 Comments: 39372
141. hurricane23
8:48 AM EST on February 22, 2007
Good morning,

Looking at Gamade this morning its looking extrememly well organized with very well established banding features...




Member Since: May 14, 2006 Posts: 8 Comments: 13841
140. Patrap
6:18 AM CST on February 22, 2007
cimss MIMIC Gamede Link
Member Since: July 3, 2005 Posts: 428 Comments: 129818
139. Patrap
6:17 AM CST on February 22, 2007
cimss MIMIC FAVIO...Link
Member Since: July 3, 2005 Posts: 428 Comments: 129818
138. mrpuertorico
8:07 AM AST on February 22, 2007
dry air continues to dominate the antilles and caribbean
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136. Raysfan70
5:47 AM EST on February 22, 2007
Good Morning {{Dr.Master's}}.
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135. HadesGodWyvern (Mod)
4:06 PM JST on February 22, 2007
10 min sustained winds stats

0600am UTC 22Feb 2007
Metro France: RSMC Reunion

Forte Tempête Tropicale Gamede
55 knots with wind gusts up to 80 knots

Cyclone Tropical Intense Favio
95 knots with wind gusts up to 135 knots

Dépression Tropicale 11R
30 knots with wind gusts up to 45 knots
Member Since: May 24, 2006 Posts: 52 Comments: 46908
134. Skyepony (Mod)
4:54 AM GMT on February 22, 2007
Favio is gonna smack the same flooded area I've posted about in the last 6 weeks.

As Floods Continue, Mozambique Now Prepares for Cyclone
Member Since: August 10, 2005 Posts: 224 Comments: 39372
133. hurricane23
11:49 PM EST on February 21, 2007
Indeed doesn't look good for those folks in the path of favio.

Gamade is developing a strong CDO.


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132. Skyepony (Mod)
4:31 AM GMT on February 22, 2007
Bad news for Africa, Favio ain't done.



Just about to make landfall


Worst winds on the SW side as well, another not good.

Looking at MIMIC it looks like that weak spell was an eyewall replacement. All done now.
Member Since: August 10, 2005 Posts: 224 Comments: 39372
131. Tazmanian
5:10 PM PST on February 21, 2007
her is what the STEERING CURRENTS look like right now

lol
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130. 882MB
1:05 AM GMT on February 22, 2007
Yes indeed Hurricane23, I am also predicting a very ACTIVE HURRICANE SEASON. NOW IT WILL ALL DEPEND ON THE STEERING CURRENTS!
Member Since: September 29, 2006 Posts: 0 Comments: 433
129. hurricane23
7:32 PM EST on February 21, 2007
The 2007 hurricane season has the potential to to end being very active if neutral conditions are around.We saw what took place in 2004-2005.

Gamede continues to get oraginzed and has the looks of a power cyclone is in the making .

Free Image Hosting at www.ImageShack.us

Member Since: May 14, 2006 Posts: 8 Comments: 13841
128. Thunderstorm2
7:36 PM GMT on February 21, 2007
More Tornadoes? We don't need anymore Tornadoes
Member Since: December 22, 2006 Posts: 129 Comments: 7608
126. Thunderstorm2
7:34 PM GMT on February 21, 2007
Indian Ocean is hot right now.
Member Since: December 22, 2006 Posts: 129 Comments: 7608
125. hurricane23
2:30 PM EST on February 21, 2007
Gamede looking quite impressive forcasted to reach 60kts which will probably intensify futher then currently forcasted if current intensification continues.


Member Since: May 14, 2006 Posts: 8 Comments: 13841
124. Tazmanian
11:27 AM PST on February 21, 2007
Posted By: weatherboykris at 10:04 AM PST on February 21, 2007.

Rand is back!Go to atmos's blog.


huh??????
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122. Skyepony (Mod)
7:25 PM GMT on February 21, 2007
FL has been getting it's share of El Niño tornados.
Member Since: August 10, 2005 Posts: 224 Comments: 39372
121. Skyepony (Mod)
7:02 PM GMT on February 21, 2007
Inyo~ Yeah, I see how in the past when it veried above or below the - or + .5 threshold it stayed there for atleast the next 5, 3 month average incroments. That's the minumum amount of time to make the La Nina or el Nino official. It's never gone above or below & ended before 5 months except in 1962, 1967 & 2005. This year offically it will probibly make it 5 months & be an offical El Nino unlike 2005 unoffical La Nina. Close though.

I don't know if I buy the big influence of ENSO as to where the high will set up for the most part & even it's affect on #s is limited. Look at 2004. That was alot for el nino year. 2005 was a cold side of neutral & an unoffical La Nina year & much land was hit as well. '79 was the warm side of neutral~ alot of landfalls. Alot of factors.
Member Since: August 10, 2005 Posts: 224 Comments: 39372
120. Inyo
6:23 PM GMT on February 21, 2007
does anyone else think the ENSO cycle is increasing in the speed of its fluxuations?


also, this El Nino had no effect on most of the US. In fact, California had La Nina type conditions. Makes you wonder what the La Nina will do
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119. weatherboykris
6:03 PM GMT on February 21, 2007
Rand is back!Go to atmos's blog.
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118. hurricane23
1:02 PM EST on February 21, 2007
Good to hear from you progressivepulse goodluck with your baby due in a few months.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
117. weatherboykris
5:57 PM GMT on February 21, 2007
I'm doing good,ProgressivePulse.
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116. hurricane23
12:56 PM EST on February 21, 2007
Very active times across the indian ocean!


Member Since: May 14, 2006 Posts: 8 Comments: 13841
115. ProgressivePulse
5:54 PM GMT on February 21, 2007
Doing well everyone! Busy with wifey and work or course, how are you all?
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114. hurricane23
12:33 PM EST on February 21, 2007
There's a good chance La nina conditions will develope somewere between march and june.Some strong El Ninos have been followed by neutral conditions or by weak La Ninas.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
113. Thunderstorm2
5:37 PM GMT on February 21, 2007
Sorry. i've got about 10 things in my mind just now
Member Since: December 22, 2006 Posts: 129 Comments: 7608
112. weatherboykris
5:35 PM GMT on February 21, 2007
La Nina isn't here yet TS2.What are you talking about?
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111. Thunderstorm2
5:32 PM GMT on February 21, 2007
When is La Nina forecast to Die out?

It's going to be quite a season
Member Since: December 22, 2006 Posts: 129 Comments: 7608
110. Thunderstorm2
5:31 PM GMT on February 21, 2007
Hi ProgressivePulse
Member Since: December 22, 2006 Posts: 129 Comments: 7608
109. hurricane23
12:31 PM EST on February 21, 2007
Tracks of landfalling hurricanes indicate that East Coast landfalling storms tend to form in the central Atlantic and curve northward just off the Leeward Islands while Florida landfalling storms are more likely to form further west. There are less storms forming in the central Atlantic, where East Coast landfalling hurricanes tend to form, during neutral years than during cold years. This may explain why there are fewer hurricanes making landfall along the East Coast than in Florida during neutral years.

Hey progessive pulse!What u been up too!
Member Since: May 14, 2006 Posts: 8 Comments: 13841
108. weatherboykris
5:29 PM GMT on February 21, 2007
Hi progressivePulse.Haven't seen you in a while.
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107. ProgressivePulse
5:24 PM GMT on February 21, 2007
Well lets just hope they stay away! New baby girl due on July 10th! Can't just stick around like we used to anymore! Hello everyone long time no talk!
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106. Thunderstorm2
5:26 PM GMT on February 21, 2007
the GOM and Carribean is normally more active in La Ninas.


Thats good to know
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105. weatherboykris
5:26 PM GMT on February 21, 2007
And not just that,H23.It ocsillates from week to week,sometimes a trough,sometimes a ridge,usually.In some years,there is mostly a ridge(2004),or a trough(2006).
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104. hurricane23
12:23 PM EST on February 21, 2007
There are also factors that can complicate the prediction of tropical cyclone steering. Trough interactions may affect the track of a tropical cyclone The position of an upper-level trough can play a role in the direction that a tropical cyclone will move. Also, tropical cyclones are known to modify their own environment. These modifications can make it difficult to predict steering.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
103. weatherboykris
5:23 PM GMT on February 21, 2007
And to answer your question,the GOM and Carribean is normally more active in La Ninas.
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102. weatherboykris
5:21 PM GMT on February 21, 2007
I'm still here.
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101. hurricane23
12:21 PM EST on February 21, 2007
Number wise they could be quite active but in la nina years alot systems recurve before reaching the united states.


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100. Thunderstorm2
5:16 PM GMT on February 21, 2007
I'm listning
Member Since: December 22, 2006 Posts: 129 Comments: 7608
99. catastropheadjuster
5:12 PM GMT on February 21, 2007
H23 & WBK are you'll gone and am i just talking to myself? I was enjoying the talk we was having.
Member Since: August 24, 2006 Posts: 21 Comments: 3683
98. catastropheadjuster
5:01 PM GMT on February 21, 2007
So by that Graph you showed La Nina could be a quite year to, I always thought La Nina made Hurricane Season worser. Or that's what I've always heard. Or am i just getting all messed up?I promise I'm not stupid or trying to be difficult.
Member Since: August 24, 2006 Posts: 21 Comments: 3683
97. catastropheadjuster
4:46 PM GMT on February 21, 2007
During La Nina years is the GOM region usually in the clear cause i see where you'll are saying Florida usually gets pounded during La Nina and something about the east coast and I just didn't know if people like Mobile,Miss,NO,TX is clear in them years. I thought i read somewhere this year where they raised the percentage up for the GOM. I may not be making no sense I don't know.
Member Since: August 24, 2006 Posts: 21 Comments: 3683
96. hurricane23
11:49 AM EST on February 21, 2007
No problem sheri...

It also tends to result in a pattern in which we have a strong Atlantic ridge that is located further to the east as the Azores High, resulting in a year like 1999 (not 2004/2005) pattern. This tends to mean a strong trough located right off the southeast/eastern U.S. coast, meaning that most Cape Verde-type storms that form far east in a La Nina pattern will likely curve away from Florida and miss the U.S. eastern coast or, if they make landfall, hit the Carolinas.Its all about timeing with tropical systems.

Typically during LA NINA years the jet stream rides further north and prevents fronts to come very far south there for outside the the rainy season we are dry down here in florida amounting to drought conditions arcoss the state.

Also wanted to mention while east hits are less common in La Nina years, Florida tends to receive more southwest hits during La Nina years than during neutral/El Nino years.

Member Since: May 14, 2006 Posts: 8 Comments: 13841
95. Comatose
11:45 AM EST on February 21, 2007
You all probably see this question a lot, and forgive me for posting it again.

What effect does La Nina have on the FL weather outlook for spring and summer? How does it effect hurricane season?
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94. catastropheadjuster
4:15 PM GMT on February 21, 2007
Hey H23 & WBK: Yes I got them thank you. I'll be able to learn from them and sometimes I like to ask questions. Sometimes I can learn from people explaining it to me better. but i like getting your info cause i can go look at it and learn from it to.
Member Since: August 24, 2006 Posts: 21 Comments: 3683
93. hurricane23
11:44 AM EST on February 21, 2007
Typically during LA NINA years the jet stream rides further north and prevents fronts to come very far south there for outside the the rainy season we are dry down here in the southeast.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
92. Thunderstorm2
4:39 PM GMT on February 21, 2007
Skye, Rand was cursing and going on about it in auburns blog at around 4am EST yeasterday. I don't think he slept all night
Member Since: December 22, 2006 Posts: 129 Comments: 7608

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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