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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Severe Thunderstorm Watch number 21
NWS Storm Prediction Center Norman OK
1255 PM EST Tue Feb 13 2007
The NWS Storm Prediction Center has issued a
Severe Thunderstorm Watch for portions of
central Florida
coastal waters
Effective this Tuesday afternoon and evening from 1255 PM until
700 PM EST.
Hail to 2 inches in diameter... thunderstorm wind gusts to 70
mph... and dangerous lightning are possible in these areas.
The Severe Thunderstorm Watch area is approximately along and 65
statute miles either side of a line from 20 miles north of Ocala
Florida to 50 miles east of fort Meyers Florida. For a complete
depiction of the watch see the associated watch outline update
(wous64 kwns wou1).
Remember... a Severe Thunderstorm Watch means conditions are
favorable for severe thunderstorms in and close to the watch
area. Persons in these areas should be on the lookout for
threatening weather conditions and listen for later statements
and possible warnings. Severe thunderstorms can and occasionally
do produce tornadoes.
Other watch information... continue... ww 20...
Discussion... tstm cluster off the W CST of FL... and additional
storms likely to from in heated environment over the interior... may
pose a threat for high wind and hail as region continues to
destablize downstream from 50 kt wly mid level jet streak. While
low level shear is weak over most of ww area... low level directional
shear will be enhanced invof E CST sea breeze boundary and outflows
from earlier storms. Part of watch number 21 along the immediate E
CST may require upgrade to tornado if it appears that discrete
storms will indeed interact with those boundaries.
Aviation... a few severe thunderstorms with hail surface and aloft
to 2 inches. Extreme turbulence and surface wind gusts to 60
knots. A few cumulonimbi with maximum tops to 450. Mean storm
motion vector 26035.
... Corfidi
;295,0811 270,0800 261,0820 291,0831
Stay Safe Chessrascal
Current radar showing thunderstorm activity will be pushing of the coast in the the next hour or so.
Weather is quite boring here in eastern NC...
Wish I had some of that snow... but will settle for a few bolts of lightning.
Weather may not be so boring for you guys during the 07 hurricane season.Be thankful its quite cause it may not last.
.TODAY AND TONIGHT...DRY WEATHER OVER THE PAST SEVERAL WEEKS HAS
INCREASED THE CHANCE FOR FIRES ACROSS PARTS OF SOUTHERN PUERTO RICO.
OTHERWISE...NO HAZARDOUS WEATHER IS EXPECTED.
look at the swirl...
look at the swirl...
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