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