2006: warmest year on record in the U.S.

By: Dr. Jeff Masters , 9:18 PM GMT on January 09, 2007

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The United States recorded its warmest year ever in 2006, according to today's report issued by the National Climatic Data Center (NCDC). The 2006 annual average temperature was 55�F, 2.2�F (1.2�C) above the 20th Century mean and 0.07�F (0.04�C) warmer than the previous warmest year, 1998. The NCDC had estimated that 2006 would be the 3rd warmest year in U.S. history last month, but an unusually warm December pushed 2006 to the top. It was the warmest December on record in the Northeast U.S., and the 4th warmest December for the country as a whole. Only 1939, 1957, and 1933 had warmer Decembers. However, the statistics partially hide the extraordinary warmth that began on December 10 and continued until January 6, when New York City tied their all-time record January high temperature of 72�. During the month ending January 6, the Northeast was 14 �F above average, and the U.S. as a whole was 7� above average.



No cause for alarm?
"No cause for alarm. Enjoy it while you have it," said Mike Halpert, head of forecast operations at the National Oceanic & Atmospheric Administration's Climate Prediction Center, in a story run by CNN just before New York City's record warmth. The story continued, "The weather is prone to short-term fluctuations, and forecasters said the mild winter does not necessarily mean global warming is upon us. In fact, the Plains have been hit by back-to-back blizzards in the past two weeks." True, the weather across most of the U.S. has finally cooled off this week, and the rest of January should have near average temperatures. And I agree that one warm month of winter in one country in its warmest year in 112 years of record keeping is not evidence of global warming, particularly when there is a moderate El Nino episode going on. An El Nino can lead to significantly warmer winters in the U.S.--exceptional December warmth has also occurred in 1877, 1939, and 1957, all of which were moderate or strong El Nino years. I've plotted up a comparison of temperatures in December of 1957 vs 2006 (Figure 1), and one can see that the unusual warmth of December 2006 does have historical precedent. Taking a look at average U.S. December temperatures for all years in the historical record (Figure 2), we see that these temperatures do show quite a bit of noise, and there is no evidence of dramatic warming in the past 30 years.


Figure 1. Comparison of the departure of average temperature from normal for December 1957 (the the second warmest December on record in the U.S.) and December 2006. Image credit: NOAA.

Figure 2. Average December temperatures for the U.S. from 1895 to 2006. Image credit: National Climatic Data Center.

Rolling thirteens with the weather dice
Take a look at the trend December temperatures in Figure 2. It shows that the average temperature has warmed a little more than 1� F in the past century. It may not seem like much, but that is enough to significantly load the dice in favor of warmer winters. Six of the ten warmest U.S. winters on record have occurred in the past 15 years. Month long spells where winter is seemingly absent--as also occurred in January 2006, the warmest January in U.S. history--have become more common. Keep in mind that the weather of January of 2006--which blew away the previous record for warmest January by a huge margin (2� F)--occurred during a La Nina year, not an El Nino. What concerns me most is that the warming trend is not isolated to the U.S. The 1� F rise in temperatures the past century has occurred world-wide, thanks to global warming, and the temperature increase has been much higher in the Arctic--something the climate models have predicted would occur as a telltale sign of the human-caused addition of greenhouse gases to the atmosphere. In the past, an exceptionally warm winter month in the U.S., like December 1957 (Figure 3), was offset by much cooler weather elsewhere, such as we see in Alaska, Greenland, and northern Siberia. However, December 2006 had no such offsetting cool temperatures--it was more than 1� C above average over almost all the land areas of the Northern Hemisphere north of 40� north latitude (Figure 4). Colorado, whose three blizzards have been widely cited as evidence that winter has been severe elsewhere, still recorded temperatures about 1� C above normal in December 2006.


Figure 3. Global departure of temperature from average for December 1957, the second warmest December on record in the U.S. Note that the exceptionally warm temperatures over the U.S. are offset by much cooler weather elsewhere, such as in Alaska, Greenland, and northern Siberia.

Figure 4. Global departure of temperature from average for December 2006. Note that the almost the entire globe north of 40� north latitude was more than 1� C above average, with large areas more than 6� C (11� F) above average.

All this unusual heat in the northern high latitudes is going to significantly slow down the formation of ice over the Arctic Ocean this winter. Furthermore, the lack of the usual snows across the Arctic may allow the snowpack to melt much earlier than normal in spring, resulting in more record warmth in the Arctic this summer. Arctic sea ice coverage, already down 20% in the past 20 years, is likely to continue to shrink in 2007. As sea ice melts in response to rising temperatures, it creates a positive feedback loop: melting ice means more of the dark ocean is exposed, allowing it to absorb more of the sun's energy, further increasing air temperatures, ocean temperatures, and ice melt. The observed changes in the ice cover (Figure 5) indicate that this feedback is now starting to take hold, and the weather dice will continue to get more loaded towards rolling higher numbers in 2007. I do think we're due for a cold winter next year--part of the warmth of the past two winters is probably due to the normal random fluctuations in the weather, and Nature has been rolling twelves more often than snake eyes of late. However, we're not going to see snake eyes too much more. December's weather in the Northeast U.S. may have been a case of the weather dice coming up thirteen--weather not seen on the planet since before the Ice Age began, 118,000 years ago. The weather dice will start rolling an increasing number of thirteens in coming years, and an ice-free Arctic Ocean in summertime by 2040 is a very real possibility, as indicated by computer modelling studies published in the Journal of Geophysical Research last month. This possibility is cause for alarm, and I, for one, had a lot of trouble enjoying the phenomenally warm weather of the past month here in Michigan.


Figure 5. Percent change in coverage of Arctic sea ice in Decembers from 1979-2006, compared to the 1979-2000 average. The Polar Ice Cap has shrunk by about 15% in December, and 20% in summer, over the past 20 years. Image credit: National Snow and Ice Data Center.

Check out the realclimate.org post on this winter's anomalous warmth.

I'll be back Thursday afternoon or Friday with a look at the status of El Nino. Will it still be around during hurricane season?

Jeff Masters

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349. txag91met
6:21 PM GMT on January 10, 2007
Satellite data does not support 2006 as warmest ever:

1998 was still warmest ever for the USA after the 1997-1998 El Nino.
The rest is growing urbanization.
1930s was still warmer if you ask me.

Global satellite temperatures below.

not there
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348. Thunderstorm2
6:10 PM GMT on January 10, 2007
Bermuda got hammered then
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346. Tazmanian
10:08 AM PST on January 10, 2007
ok
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345. Thunderstorm2
6:07 PM GMT on January 10, 2007
people only run for their lives at the last moment and by the time their out of the way of the storm or blob the system is about 300 miles away
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344. HurricaneMyles
6:06 PM GMT on January 10, 2007
LOL! We'll have plenty of time to run for our lives once the first little blob starts to fester.
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343. Thunderstorm2
6:04 PM GMT on January 10, 2007
no EL NINO all i can say is run for your lives

We don't need to run for our lives yet
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342. Patrap
11:57 AM CST on January 10, 2007
LOL...its Weds at least.
Member Since: July 3, 2005 Posts: 423 Comments: 127807
341. hurricane23
12:55 PM EST on January 10, 2007
Neutral ENSO conditions are expected to return during the southern autumm according to the Australians.
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340. Tazmanian
9:53 AM PST on January 10, 2007
no EL NINO all i can say is run for your lives
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339. Frozencanuck
5:43 PM GMT on January 10, 2007
Cyclonebuster has a love in with his tunnels. Enough already. Move on to something that is worthy for intellectual discussion regarding the weather. Find an alternative that will help now and cost little to implement, like common sense and how to reduce the greenhouse effect.
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337. HurricaneMyles
5:41 PM GMT on January 10, 2007
Buster, shear doesnt fall just becauses its summer. There are far more things involved then that. Which is why you can have periods of low shear during winter and high shear during summer.
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335. Thunderstorm2
5:37 PM GMT on January 10, 2007
isn't it
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334. hurricane23
12:37 PM EST on January 10, 2007
EL NINO IS NOW WEAKING!!

All the main ENSO indicators show that the El Nio event has begun to weaken. This bodes well for a switch towards wetter conditions across Australia sometime in the late summer or autumn. The timing of the weakening also fits in well with that observed during previous events, although it is still possible for there to be renewed strengthening of the El Nio event for a month or two before it finally dissipates.

ENSO UPDATE

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333. HurricaneMyles
5:36 PM GMT on January 10, 2007
Buster...I want to know what scientific basis you have for global warming creating less shear and year round hurricane seasons. Please show me where you have any proof that global warming will reduce shear.
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328. Thunderstorm2
5:26 PM GMT on January 10, 2007
Bottom line is the tunnels have the world in checkmate either we build them or we become an endangered species!

that is a good point
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324. Thunderstorm2
5:20 PM GMT on January 10, 2007
you must really love your tunnels
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318. Thunderstorm2
5:06 PM GMT on January 10, 2007
Posted By: cyclonebuster at 5:01 PM GMT on January 10, 2007
Don't kid yourself it will be here in a blink of your eye!


well true it seems like half a year since the end of the 2005 HS
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315. Thunderstorm2
4:57 PM GMT on January 10, 2007
still a long time to go, 23 years
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313. Snowfire
4:56 PM GMT on January 10, 2007
I notice that in 1957 there was still genuine cold air up in Canada. The warmth of that year was a function of that air being pinned north by the jet stream. In contrast, the 2006 map shows no significantly cold air anywhere. Yes, we may be getting a northerly jet stream at the moment, but this is clearly different. Where are the -50s, -60s, and -70s up north that preceded the great Arctic outbreaks of the past? Nowhere. Even the Canadian Arctic has seen few temperatures colder than -30 this season. Even a flip of the jet stream can deliver only a weak imitation of the cold outbreaks that were common 20 and more years ago. The really cold air just isn't there, and it keeps on not being there.
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311. Thunderstorm2
4:54 PM GMT on January 10, 2007
in about the year 2030
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310. ProgressivePulse
4:47 PM GMT on January 10, 2007
2005 hurricane season was plagued with african dust coupled with La Nina. 2007 Has a possibility to be near or below normal in the dust catagory coupled with a nuetral to la nina event. I agree it has the possibility to be an active season but, thankfully we don't have to worry about that for many months.
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308. Thunderstorm2
4:49 PM GMT on January 10, 2007
They can just maintain themself over cool waters
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304. Thunderstorm2
4:45 PM GMT on January 10, 2007
thats actully true
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303. weatherboykris
4:45 PM GMT on January 10, 2007
be back later
Member Since: December 9, 2006 Posts: 125 Comments: 11346
302. weatherboykris
4:43 PM GMT on January 10, 2007
I can't remember where, but I read somewhere that once SSTS reach 83F, they cease being a factor in hurricane strength.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
301. weatherboykris
4:42 PM GMT on January 10, 2007
we're in the warm AMO.Too many people are calling the past 11 years global warming without doing the research.
Member Since: December 9, 2006 Posts: 125 Comments: 11346

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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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