Arctic climate change: the past 100 years
The Arctic is a region particularly sensitive to climate change, since temperatures are, on average, near the freezing point of water. Slight shifts in the average temperature can greatly change the amount of ice and snow cover in the region, due to feedback processes. For example, as sea ice melts in response to rising temperatures, more of the dark ocean is exposed, allowing it to absorb more of the sun's energy. This further increases air temperatures, ocean temperatures, and ice melt in a process know as the "ice-albedo feedback" (albedo means how much sunlight a surface reflects). The 20% loss in Arctic sea ice in summer since 1979 has given rise to concerns that this "ice-albedo feedback" has taken hold and will amplify until the Arctic Ocean is entirely ice-free later this century. Should we be concerned? Has the Arctic been this warm in the past and the sea ice survived? The answers are yes, and yes.
Figure 1. Annual average change in near surface air temperature from stations on land relative to the average for 1961-1990, for the region from 60 to 90° north. Image credit: The Arctic Climate Impacts Assessment (ACIA).
The past 100 years
The Arctic Climate Impact Assessment (ACIA), published in November 2004, was a uniquely detailed study of Arctic climate compiled by 300 scientists over three years. The study found that while temperatures in the Arctic have increased significantly since 1980 (Figure 1), there was also a period in the 1930s and 1940s when temperatures were almost as warm. If one defines the Arctic as lying poleward of 62.5° north latitude (Polyakov, 2003), the 1930s and 1940s show up being warmest period in the past 100 years. Looking at Figure 1, one cannot dismiss the possibility that temperatures in the Arctic oscillate in a 50-year period, and we are due for a cooling trend that will take temperatures below normal by 2030.
However, the period since 1980 was a time when the entire globe (except the bulk of Antarctica) warmed, and the 1930s and 1940s were not. Thus, the 1930s and 1940s warming in the Arctic is thought to be fundamentally different. Furthermore, the past 20 consecutive years have all been above normal in temperature, whereas during the 1930s and 1940s there were a few cooler than average years interspersed with the very warm years. A detailed breakdown by month and region of the 100-year history of Arctic temperatures was performed by Overland et al. (2004). They found no evidence of a 50-year cycle in Arctic temperatures, and concluded that the warming since 1980 was unique. However, they stopped short of blaming the recent warming on human-emitted greenhouse gases (anthropogenic forcing). The ACIA, though, concluded that humans were likely to blame for the recent Arctic warming, but not definitely:
It is suggested strongly that whereas the earlier warming was natural internal climate-system variability, the recent surface air temperature changes are a response to anthropogenic forcing. There is still need for further study before it can be firmly concluded that the increase in Arctic temperatures over the past century and/or past few decades is due to anthropogenic forcing."
This is the first 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: The skeptics attack the ACIA report--and how the position of the pole star is indicative of Arctic climate change.
Also, be sure to visit our new Climate Change blog, written by Dr. Ricky Rood of the University of Michigan.
Jeff Masters
References
Overland, J.E, M.C. Spillane, D.B. Percival, M. Wang, H.O. Mofjeld (2004), "Seasonal and Regional Variation of Pan-Arctic Surface Air Temperature over the Instrumental Record", Journal of Climate, 17:17, pp3263-3282, September 2004.
Polyakov, V., et al. (2003), "Variability and Trends of Air Temperature and Pressure in the Maritime Arctic, 1875-2000", Journal of Climate, 16, 2067-2077.
Reader Comments
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Currently a radar indicated tornado visible on Intellicast's stormwatch thingy. 2 rotating storms near the GA\SC border.
All day thunderstorms have been poping up about 10 miles to the east of my area. There was a few good thunderstorms today.
Nexsat
cmc slightly warm..I agree how this & the next ones takes it as the low that has been treking across instead of a new storm that forms in the Atlantic.
Nogaps
& the winner for most crazy warm storm, 2 nights in a row is, the, Ukmet...
Did you atleast see a drop of rain lightning?
1 15.0 inches Feb. 28, 1900
2 13.3 inches Jan. 1-2, 1999
3 12.6 inches Jan. 30-31, 1914
4 11.1 inches Feb. 12-13, 2007
5 10.9 inches Dec. 19, 1973
6 10.7 inches Feb 12, 1894
7 10.5 inches Dec 24, 1915
8 10.3 inches Feb 23-24, 1965
9 9.4 inches Mar. 19-20, 1906
10 9.0 inches Feb. 15, 1903
NWS Central Illinois
Notice that 5 of these occur in February...
I'll trade you guys out West any day for the Ice Storm and Cold Weather We're having right now in NYCity ANY DAY!!!
Be Careful for what you wish for!!!
Wednesday, February 14, 2007
By Mark Schleifstein
National Weather Service forecasters issued an eerily accurate forecast 24 hours before a thunderstorm produced at least one tornado that ripped across the West Bank of Jefferson Parish and New Orleans early Tuesday.
On Monday at 3:24 a.m., forecasters in the Slidell office of the National Weather Service warned of tornadic supercell thunderstorms, accompanied by winds as high as 79 mph, golf ball-sized hail and the potential of a tornado ranked as a 3 on the new Enhanced Fujita Scale.
It estimates wind speed on a scale of 1 to 5, based on damage measured on the ground after the event. A 3 is equivalent to winds of 136 to 165 mph.
Robert Ricks, the lead forecaster who oversaw the meteorologists on duty during the early mornings both Monday and Tuesday, said that in approving the forecast, he relied on only one of several weather forecast models that predicted the tornadic storms would form. The other models, he said, indicated the storms would form later in the day on Tuesday.
Weather officials quickly doubled their forecasters on duty early Tuesday. And Monday at 3 p.m., they briefed emergency operations personnel in parishes throughout southeastern Louisiana about the upcoming storms.
Adding to the concern, Ricks said, was the memory of the Feb. 2 tornado that cut a wide swath through central Florida, killing 20 people. That twister had dropped from the sky in the middle of the night, catching many residents unaware, including a number who lived in trailers.
Ricks said his staff had carefully watched the forecasting measures taken by their cohorts in Florida, especially the problems caused by the early-morning arrival. That resulted in additional language added to forecasts during the day Monday, warning people living in FEMA trailers to watch the skies and find shelter in the event of a thunderstorm.
By the time Ricks returned to duty in Slidell at midnight Monday, the forecast was turning into reality.
Forecasters were watching so-called "rogue cell" thunderstorms form in advance of a squall line of connected thunderstorm activity that had formed well in advance of a strong cold front.
"We put up a (weather) balloon at midnight, and it came back with readings showing that the air mass had really destabilized quickly, compared to the 6 p.m. balloon," Ricks said. "The moisture content was much deeper, and the spin of winds at different levels was like going up a spiral staircase, increasing in speed as you go up in the atmosphere." "I remember making a comment to the radar operator that that's bad news for the city of New Orleans," Ricks said.
The office issued the first warning at 2:28 a.m.: A potential tornado was heading toward Boutte, Hahnville, Metairie and Kenner. That was 34 minutes in advance of the first damage in Westwego, Ricks said. The storm moved east, and warnings followed for Marrero, Harvey, Avondale, New Orleans and Chalmette
A 3:12 a.m. update added the Lower 9th Ward, Arabi and an area south of Lakefront Airport. Forecasters said that was a second tornado dropping from the same thunderstorm, which cut through Pontchartrain Park.
On Tuesday, a National Weather Service team surveyed the damage and concluded the supercell created two separate tornadoes. The first carved a path two miles long and 50 yards wide across the West Bank, beginning in Westwego, as an F2 on the Enhanced Fujita Scale, with winds estimated between 111 and 135 mph. It then jumped the Mississippi River and weakened to F1 strength, between 86 and 110 mph, cutting through Uptown and Carrollton.
Forecasters said a second tornado, also an F2, descended near the intersection of Franklin Avenue and Mendez Street, then cut across Pontchartrain Park to the Industrial Canal.
"It's very rare to see two F2 tornadoes touch down in New Orleans on the same day, only five or six miles away from each other," National Weather Service forecaster Phil Grigsby said.
Before Tuesday, only 14 tornadoes had touched down in New Orleans since 1950, according to the National Climatic Data Center.
State Climatologist Barry Keim said that April is the peak month for tornadoes in Louisiana, with a secondary peak in November. Between 1880 and 1989, there were 36 tornadoes ranked F1 or stronger in February in Louisiana, compared with 74 in April. Twisters are least common in summer, Keim said.
Daniel McCarthy, warning coordination meteorologist for the National Weather Service's National Storm Prediction Center in Norman, Okla., said the Tuesday tornadoes should reinforce the weather service's efforts to get people to buy National Oceanic and Atmospheric Administration weather radios. The radios can be programmed to turn on automatically when a tornado or other dangerous weather event occurs.
"I think it's imperative that you keep an eye on the weather when the Storm Prediction Center issues a warning," he said. "When a tornado watch is issued, you need to keep abreast of the situation, even at 3 in the morning."
Link
Was never near one, but seen what they can do
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