Atmospheric Climate Modes and the Recent “Arctic Warm” Period
Or Where will the Polar Bears Go?James Overland
NOAA/Pacific Marine Environmental Laboratory, Seattle, USA
SAT
SLP
Sample: Arctic Oscillation (AO) and “Pacific” Surface Air Temperature (SAT) and Sea Level
Pressure (SLP) Anomalies
+PNA-AO
1977-1988
+AO1989-1995
Quadrelli and Wallace2004
A) AO Pattern found by
Exner (1913)!
AO/
AO
PNA*
Meridional
Spitzbergen and Arctic SAT
Mean SAT North of 60° N
-1.5
0.0
1.5
1850 1870 1890 1910 1930 1950 1970 1990 2010
Year
SAT
Anom
aly
(Std
. Dev
.)
Spitzbergen
-10
-5
0
5
10
1910 1915 1920 1925 1930 1935 1940
Tem
p. A
no
mal
y (
°C )
1040985 mb
SLP1938
Recent WARM Period Spring SAT and SLP Anomalies
SATSPRING
2000-2005
SAT2006-2007
SLPMeridional
Recent Winter SAT and SLP Anomalies
SATWinter2000-2005
SLP
SAT2006-2007
The Unusual Multi-year Meridional Patterns had Much to do with Ocean and Sea Ice
Preconditioning, But Summer 2007 SLP field was also Rare Event
19771987 2007
19771987 2007
19771987 2007
Recent (2005-2007) Fall SAT AnomaliesGreater than +6 C!
The Meridional Pattern is Over;The Positive AO returns in 2007 and 2008
SLP SAT
Atmospheric Changes: Temperature and Modes-of Variability
Need three Climate Patterns to describe Arctic: AO, Pacific, and 3rdPattern (Meridional/Dipole) The Plus AO returns!
Last Decade is unique compared to 20th Century: 1)Arctic-wide temperature anomaly (+1-2 C) Global warming signal? 2) +AO in 1990s and RARE Meridional Pattern the last decade Natural Variability gave very warm pattern over central Arctic 3) MAJOR Fall Warm Anomalies due to lack of summer sea ice
Both AO and Meridional patterns contributed to preconditioning ocean and sea ice in the Pacific Sector
DEEP HISTORY+2-3 C above 20th century between 11,500 and 9000 years before present on north slope of Alaska
Bowhead populations from 10,500 to 8,500 year before present (BP) had a range in summer from the Beaufort Sea through to Baffin Bay. For 5,000 to 3000 BP bowheads reoccupied the central channels of the Arctic Islands beyond historical limits
In the last 700 years it was mainly cold from 1240-1520 and 1730-1920 and warm from 1520-1730 and after 1920