The pole star and Arctic climate change

By: Dr. Jeff Masters , 5:01 PM GMT on February 15, 2007

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Hello Weather Underground bloggers, Aaron here. Dr. Masters is on vacation so I'll be posting a series of vacation blogs for him. This is the first.

In my previous blog, I mentioned how the Arctic Climate Impact Assessment (ACIA), a 2004 study of Arctic climate compiled by 300 scientists over three years, found that the recent increase in Arctic temperatures was probably due to human-emitted greenhouse gases. Greenhouse skeptics attacked the ACIA report and its conclusion, pointing out that the Arctic was much warmer than today during the period 4,000 - 7,000 years ago. For example, Dr. Patrick Michaels said in a 2004 interview with CNS news, a conservative Internet news service:"It was warmer 4 to 7,000 years ago [in the Arctic.] Every climatologist knows that. I saw no mention of that in the Arctic report," Michaels said. He added that the past warming of the Arctic couldn't possibly be blamed on greenhouse gas emissions since it occurred long before the industrial era.It is true that Arctic summers were warmer during the period 4,000 - 7,000 years ago. The mean July temperature along the northern coastline of Russia may have been 2.5 to 7.0 �C warmer than present, and Scandinavian summer temperatures were 1.5 to 2 �C higher than at present. The warming was caused by changes in the amount of sunlight the north pole gets in summer due to variations in the Earth's orbit.
Figure 1. Summertime temperatures in the Arctic during the Mid-Holocene Warm Period (about 6,000 years ago), compared to today's temperatures. Image credit: NOAA.

Earth's orbital variations
Earth's orbit is not perfectly circular, which means that we are closest to the sun in December and farthest in July. Thus, the Southern Hemisphere gets more sunlight in their summer (December) than the Northern Hemisphere does in their summer (July). The Earth's current 23.5 degree tilt keeps the north pole pointed towards the star Polaris, which results in the north pole being pointed at the sun in December (Northern Hemisphere winter). The Earth slowly wobbles around its axis with a period of 23,000 years a href=(precession) so that the pole star gradually changes with time. During the period 4,000 - 7,000 years ago, the pole star was Thuban in the constellation Draco, and the north pole was pointed at the sun during Northern Hemisphere summer. This resulted in much warmer summer temperatures in the Arctic, since there was more summer sunlight. Conversely, winter temperatures were colder, since the Earth was farther from the sun during the Northern Hemisphere winter. The Arctic will again be much warmer in summer 16,000 to 19,000 years from now when the cycle repeats and Thuban is once more the pole star. The reason the ACIA failed to mention this climate period is that the average temperature in the Arctic remained about the same during the period 4,000 - 7,000 years ago; it was just the summers that warmed. The warming since 1980 and the 1930s were warmings over all seasons, so it was misleading for the climate skeptics to compare Arctic temperatures 4,000 - 7,000 years ago with these modern warmings.

This is the second in a series of five blogs on climate change in the Arctic that will appear every Monday and Thursday. Next blog: Why the Arctic sea ice is shrinking.


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

Jeff Masters

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326. Skyepony (Mod)
10:26 PM GMT on February 20, 2007
Can't get into FSU models & what not.

When this blog is this slow always seems aproprate to post the Duldrums. N of Aulstralia is a bad spot for Duldrums this time of year. Their 'cane season should be picking up soon.
Member Since: August 10, 2005 Posts: 293 Comments: 41048
325. Skyepony (Mod)
10:22 PM GMT on February 20, 2007
Surface map with the 953mb low in the Atlantic.
Member Since: August 10, 2005 Posts: 293 Comments: 41048
324. Skyepony (Mod)
10:21 PM GMT on February 20, 2007
Member Since: August 10, 2005 Posts: 293 Comments: 41048
323. Thunderstorm2
8:52 PM GMT on February 20, 2007
I can't find the site but its on Taz's Blog. It's the last picture.
Member Since: December 22, 2006 Posts: 130 Comments: 7608
322. pottery
8:47 PM GMT on February 20, 2007
No I did not see that low. Can you link it ?
Member Since: October 24, 2005 Posts: 0 Comments: 25533
321. Thunderstorm2
8:46 PM GMT on February 20, 2007
What
Member Since: December 22, 2006 Posts: 130 Comments: 7608
320. pottery
8:45 PM GMT on February 20, 2007
er, 27 is out too.......
Member Since: October 24, 2005 Posts: 0 Comments: 25533
319. Thunderstorm2
8:43 PM GMT on February 20, 2007
Have you seen that 950mb low that is in the Atlantic?
Member Since: December 22, 2006 Posts: 130 Comments: 7608
318. pottery
8:40 PM GMT on February 20, 2007
The satelite images are showing some cloud across the trop. atlantic for the first time in a couple of weeks. Looks like things are setting up for more showers ? I hope so ......
Member Since: October 24, 2005 Posts: 0 Comments: 25533
317. Thunderstorm2
8:40 PM GMT on February 20, 2007
ihave27handguns
Member Since: December 22, 2006 Posts: 130 Comments: 7608
316. Thunderstorm2
8:36 PM GMT on February 20, 2007
Rand might be back. Come to Rays Blog. I think he is under the name "ihave27handguns"
Member Since: December 22, 2006 Posts: 130 Comments: 7608
315. pottery
8:36 PM GMT on February 20, 2007
Hi Pat. OK. Hows your Carnival today ? It actually rained on some of ours, but the Masqueraders did not seem to notice. Just got home, exhausted, dont have the energy that I used to. Wonder why ?
Member Since: October 24, 2005 Posts: 0 Comments: 25533
314. Wishcasterboy
8:35 PM GMT on February 20, 2007
Life goes on. I have a feeling we'll see them once more.
313. Tazmanian
8:33 PM GMT on February 20, 2007
it was some in that went on last night
Member Since: May 21, 2006 Posts: 5093 Comments: 115957
312. pottery
8:32 PM GMT on February 20, 2007
Whatever the reason, I'll miss both of them. I appreciated their knowledge and their comments.
Member Since: October 24, 2005 Posts: 0 Comments: 25533
311. Patrap
8:31 PM GMT on February 20, 2007
Member Since: July 3, 2005 Posts: 433 Comments: 132815
310. Thunderstorm2
8:29 PM GMT on February 20, 2007
{{Changed comment!}}
Member Since: December 22, 2006 Posts: 130 Comments: 7608
309. Patrap
8:29 PM GMT on February 20, 2007
Words of advice..let it go.Open a beer .And move along..Its a parade route..Dont gossip like a Soap ..it looks bad.Use Wu-mail..Er now back to Mardi Gras..Urp!
Member Since: July 3, 2005 Posts: 433 Comments: 132815
308. pottery
8:25 PM GMT on February 20, 2007
What happenened ? They been cussing each other out in public or what ?
Member Since: October 24, 2005 Posts: 0 Comments: 25533
307. pottery
8:23 PM GMT on February 20, 2007
I dont remember it ever raining here on a carnival tuesday before today, but it did this time . Strange portents ????????
Member Since: October 24, 2005 Posts: 0 Comments: 25533
306. Thunderstorm2
8:21 PM GMT on February 20, 2007
Yes Pottery. He has been banned and so has STL
Member Since: December 22, 2006 Posts: 130 Comments: 7608
305. pottery
8:18 PM GMT on February 20, 2007
Has Randrewl been zapped ? All references to him have gone, from previous blogs too. Whats up with that ??????
Member Since: October 24, 2005 Posts: 0 Comments: 25533
304. weatherboykris
8:02 PM GMT on February 20, 2007
What happened to Rand?His blog disappeared.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
303. Patrap
7:49 PM GMT on February 20, 2007
Member Since: July 3, 2005 Posts: 433 Comments: 132815
302. Caffinehog
7:46 PM GMT on February 20, 2007
Interesting low WNW of madagascar. Looks tropical on the satellite, but quickscat shows it as quite asymmetrical, a SW-NE trough.
What's going on with this one?
Member Since: June 5, 2003 Posts: 0 Comments: 40
301. Thunderstorm2
7:16 PM GMT on February 20, 2007
The fishin' Game?
Member Since: December 22, 2006 Posts: 130 Comments: 7608
300. Patrap
7:15 PM GMT on February 20, 2007
MArdi Gras in Full Swing Under PArtly Cloudy to Partly sunny skies...7
Member Since: July 3, 2005 Posts: 433 Comments: 132815
299. Thunderstorm2
7:12 PM GMT on February 20, 2007
around 100 days to H Season. Aaron please update this blog
Member Since: December 22, 2006 Posts: 130 Comments: 7608
298. catastropheadjuster
7:10 PM GMT on February 20, 2007
Hey TS2 & TAZ boring day on the blog and yes it needs to be updated it's been the same for about 2 or 3 days know. I wish they would talk about La Nina and the Neutral conditions I think that would be kinda interesting.I know we have a while til hurricane season but still at least that would be a interesting topic.
Member Since: August 24, 2006 Posts: 21 Comments: 3683
297. Thunderstorm2
7:05 PM GMT on February 20, 2007
Favio has looped round the south of Madagascar without making landfall on the island. I think thats weird
Member Since: December 22, 2006 Posts: 130 Comments: 7608
296. Tazmanian
7:04 PM GMT on February 20, 2007
some one needs to update the dr m blog
Member Since: May 21, 2006 Posts: 5093 Comments: 115957
295. catastropheadjuster
7:01 PM GMT on February 20, 2007
Is anyone here? It seems so quite on this blog, we'll it's been that way for a while I guess it will get busy come hurricane season. I heard someone saying that the something called Autralian comes out on Feb 21. What will that kinda let us know if Neutral conditions are going on know or what. And what about La Nina?
Member Since: August 24, 2006 Posts: 21 Comments: 3683
294. Patrap
3:01 PM GMT on February 20, 2007
Member Since: July 3, 2005 Posts: 433 Comments: 132815
293. TayTay
3:00 PM GMT on February 20, 2007
g
292. mrpuertorico
11:47 AM GMT on February 20, 2007
oh and a heavy surf advisory is up!!! and i am stuck at work :(
Member Since: July 10, 2006 Posts: 1 Comments: 833
291. mrpuertorico
11:45 AM GMT on February 20, 2007
well benerica it sure has been raining here in pr this morning .79 inches lol! but could expect another 2 days of rain woooooot!
Member Since: July 10, 2006 Posts: 1 Comments: 833
284. HadesGodWyvern (Mod)
7:07 AM GMT on February 20, 2007
Metro France now reports an Intense Tropical Cyclone Favio with 10 min sustained winds of 90 knots with wind gusts up to 130 knots. The systems center pressure is 945 hPa.
Member Since: May 24, 2006 Posts: 56 Comments: 49944
283. benirica
4:10 AM GMT on February 20, 2007
Call it El Nino, call it Global Warming or just call it a weather pattern, but this winter has been freackin hot here in Puerto Rico and the drought began alot earlier. It usually stops raining here by march, but we havent got much rain here at all for about two months already!
Member Since: August 3, 2006 Posts: 0 Comments: 1143
282. weatherhunter
3:03 AM GMT on February 20, 2007
CARIBBEAN SEA...
THE TAIL END OF A COLD FRONT IS PRESENTLY OVER THE VIRGIN
ISLANDS ALONG 20N62W 16N70W MOVING RAPIDLY E. LIGHT RAIN AND
GUSTY WINDS OF 25 KT ARE ALONG THE FRONT. THIS IS THE FIRST
COLD FRONT TO ENTER THE LEEWARD ISLANDS THIS WINTER.
NELY
SURFACE WINDS WITH SCATTERED SHOWERS ARE BEHIND THE FRONT W OF
70W. THE SE CARIBBEAN AND WINDWARD ISLANDS S OF 15N AND E OF
70W ARE THE ONLY AREAS WITH LIGHT TRADEWINDS WITH PATCHES OF
BROKEN LOW CLOUDS AND SCATTERED SHOWERS. IN THE UPPER LEVELS...
RIDGING COVERS THE ENTIRE CARIBBEAN SEA WITH STRONG SUBSIDENCE
SUPPRESSING THUNDERSTORM ACTIVITY. EXPECT THE COLD FRONT TO
CONTINUE TO THE CENTRAL ATLANTIC DURING THE NEXT 24 HOURS.

281. hurricane23
1:19 AM GMT on February 20, 2007
Winds are now up to 80 kts on Favio...

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Member Since: May 14, 2006 Posts: 8 Comments: 13848
280. hurricane23
1:14 AM GMT on February 20, 2007
(100) days exactly till it starts all over again.Take advantage off this time and get ready for what end up being quite a ride this season.
Member Since: May 14, 2006 Posts: 8 Comments: 13848
279. hurricane23
9:35 PM GMT on February 19, 2007
Eye becoming better defined on modis...

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Forcast Path

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Member Since: May 14, 2006 Posts: 8 Comments: 13848
278. Trouper415
9:27 PM GMT on February 19, 2007
Good day everyone

Peace On Earth
Member Since: September 22, 2005 Posts: 5 Comments: 648
277. hurricane23
6:40 PM GMT on February 19, 2007
Pinhole eye clearly visible on infrared imagery...

Conditions are forcasted to remain quite favorable for intensification with a lanfall near the mozambican coastline.


Member Since: May 14, 2006 Posts: 8 Comments: 13848

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Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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