Challenges in Projecting Ocean Climate Change in the NW Atlantic

John Loder 1, Augustine van der Baaren 1, Eugene Colbourne 2, Guoqi Han 2, Dave Hebert 1, Bill Merryfield 3, Ingrid Peterson 1 and Igor Yashayaev 1 1 Fisheries and Oceans Canada (DFO), Bedford Institute of Oceanography 2 DFO, Northwest Atlantic Fisheries Centre 3 Environment Canada (EC), Canadian Centre for Climate Modelling and Analysis (CCCMA)

Steps in Projecting Climate Change: • Observations, Analyses, Description, Interpretation, Attribution, etc • Understanding, Models, Validation, Projections, Uncertainty, etc

Many Challenges in observing and simulating a complex nonlinear multi-component system with variability on many time scales & uncertain forcing

Today: Spatial and Temporal Variability affecting the NW Atlantic Ocean - Short datasets, natural “decadal-scale” variability, down-scaling challenges

Special Acknowledgements to DFO’s Atlantic Zone monitoring programs (AZMP, AZOMP), its Aquatic Climate Change Adaptation Services Program (ACCASP), and the climate change science community

Ocean Climate of the NW Atlantic

Key Variables (Dynamic, Thermodynamic) Ocean: Temperature, Salinity, Sea Ice, Sea Level, Circulation (gyres and AMOC) Atmosphere (Forcing): Temperature, Precipitation, Circulation and Winds Terrestrial: Run-off, Glaciers, Ice Sheet (Greenland)

• With a “mean” or low-frequency focus, the above ocean variables (or their volume averages) are “integral” or “cumulative”

Many Other Important Aspects of Ocean Climate

• Spatial and temporal structure, e.g. fronts, stratification

• Biogeochemical properties that are influenced by, and also affect, climate

• Extreme events which depend on both low- and high-frequency variability

• All can contribute to ecosystem and coastal zone changes

Focus today on: - Temperature & Salinity - Trends & “Decadal-scale” (years to decades) variability

Upper-Ocean Water Mass Properties in the NW Atlantic: Pronounced influences of Arctic outflows, the horizontal gyres and their western boundary currents – the Gulf Stream and the Labrador Current

Annual-Mean Climatologies at 50m

T S

I. Yashayaev

Subpolar gyre

Mid-latitude transition zone

Subtropical gyre

Arctic outflows

Importance of FW from run-off, Arctic and Greenland

Large-Scale Circulation of the North Atlantic

Variability in the upper-ocean gyres and AMOC strongly influences ocean climate in the NW Atlantic

Gulf Stream

Labrador Current

3D: Atlantic Meridional Overturning Circulation (AMOC)

Cold Currents

Warm Currents

Upper-Ocean Gyres

Mean Sea Surface Height (relative to Geoid)

Note: - drop of ~2m between subtropical & subpolar gyres - drop of over 1m from Gulf Stream to Scotian Slope - 1m trough in mid-latitude transition zone associated with tail of the subpolar gyre

Relative Sea Level Rise due to Glacial Isostatic Adjustment

(Peltier 2004)

Changes from +6mm/yr (Lab Sea) to -3 mm/yr (NE GSL) => 1m difference in 100yrs

Climatological Seasonal Variation in Sea Ice Concentration (HadISST)

Seasonal change in latitudinal extent from 75N (Nares Strait in Sept) to 45N (Eastern Scotian Shelf in March)

March

November September

May January

July

A. van der Baaren

Past Variability in Surface Temperatures

NASA Hadley Centre

No warming in N Hemisphere during 1945-1975 due to aerosols & other – decadal variability

Trends

Cooling south of Greenland since 1900 but warming since 1979 – temporal & spatial variability

1979-2005 1900-2005

IPCC 2007

SST Air

AIR

Nuuk

-5-4-3-2-1012345

1860 1880 1900 1920 1940 1960 1980 2000

Tem

pera

ture

Ano

mal

y (°C

)

St. John's

-5-4-3-2-1012345

1860 1880 1900 1920 1940 1960 1980 2000

Tem

pera

ture

Ano

mal

y (°C

)

Trends (oC/century)

Iqaluit 1.1

Nuuk 0.6

Cartwright 0.5

St John’s 1.1

Shearwater 1.4

Boston 1.7

Coastal Air Temperatures around the NW Atlantic (since late 1800s)

Nuuk

St. John’s

Boston Shearwater Lowest at Nuuk & Cartwright Highest at Boston & Shearwater

Widespread decadal-scale variability including no overall warming during 1950-1990 Apparent contribution from larger-scale variation Colbourne

& Hebert

Hebert et al.

Positive NAO leads to severe winters over the Labrador Sea & NL Shelf

Variability in Atmospheric Circulation: e.g. North Atlantic Oscillation (NAO)

Positive Phase

Negative Phase

Anomalies in Winter NAO Positive phases in 1900s, 1920s 1970s, 1990s

Negative phases in 1880s, 1910s, 1930s, 1960s, 2010s

Important contributor to decadal-scale ocean variability, but other atmospheric forcing also involved, e.g. wind stress curl & blocking

-15

-10

-5

0

5

10

1950 1960 1970 1980 1990 2000YEAR

PR

ESSU

RE

(MB

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1950 1960 1970 1980 1990 2000

SEA

IC

E A

REA

NL CIL WATER MASS

0

10

20

30

40

50

60

1950 1960 1970 1980 1990 2000

CIL

AR

EA (

KM

2 )

N L CIL WATER MASS

Ocean Variability off Newfoundland & Labrador associated with the NAO

Positive NAO => More Sea Ice & Cold Water

E. Colbourne

NAO

Sea-Ice Extent

Negative NAO • warmer bottom temperatures over the Labrador-Newfoundland Shelf, Gulf of St. Lawrence and the eastern Scotian Shelf (Direct); • colder than normal conditions over central and western Scotian Shelf and Gulf of Maine (Indirect).

Temperature Anomaly

NL Shelf Cold Water Mass

B.Petrie, BIO

Subpolar Gyre Extension associated with Low NAO in the 1960s

K. Drinkwater, IMR Bergen

Shelf Bottom Temperatures

-15

-10

-5

0

5

10

1950 1960 1970 1980 1990 2000YEAR

PRES

SURE

(MB)

D. Hebert, BIO

Low NAO in 1960s: Enhanced extension of subpolar gyre west of Grand Bank

High NAO in 1970s: Retraction of subpolar gyre

Related NAO effects on Gulf Stream position

Temperature, Salinity & Dissolved Oxygen at Depth in the Gulf of St. Lawrence

Gilbert et al. (2004) Galbraith et al. (2011)

Overall increase in T & S at 300m since 1930s

T increase & DO decrease at 300m in Estuary since 1930s

Long-term increase in “subtropical” influence?

Northward creep of the subtropical gyre?

SST Variability on the Scotian Shelf and in the Labrador Sea since 1900 From HadISST1

Scotian Shelf

Labrador Sea

Different long-term and decadal-scale variability in Labrador Sea and “mid-latitude transition zone”

NAO- in 1960s

Widespread positive trend since 1980

ICES BPE WG

Baffin Bay &-Labrador Shelf/Sea

Gulf St Lawrence to Mid Atl Bight

South Greenland & NW Corner

Newfoundland Shelf & Basin

HadSST1 since 1900 at Other Sites Trends - All significant positive except SG&NWC

Small negative trend

Different decadal-scale variability among the regional groups

1900 2000 2000 1900

A. van der Baaren

Trends (oC/decade) since 1900 - weak south of Greenland - 0.04-0.05 in Baffin-Labrador - 0.07-0.08 off Newfoundland & in Slope Water - 0.11-0.13 from Scotian Shelf to Mid Atl Bight Range of 0.04-0.13 oC/dec Increase of 0.4-1.4oC since 1900

Trends (oC/decade) since 1979 - 0.2-0.3 in Baffin & shelf regions

- 0.4-0.7 in offshore regions

Range of 0.2-0.7oC/decade

Increase of 0.6-2.1oC since 1979

Increased widespread warming in past few decades

A. van der Baaren

HadSST1 Trends since 1900 and since 1979 (oC per century)

1900-2011 1979-2011 1.5 8

1 0

Trends have different patterns and magnitudes for different periods, due to spatial structure in decadal-scale variability => Difficulty in unravelling natural and anthropogenic variability

A. van der Baaren

GRL2012

Ocean heat content increasing in 700-2000m depth range, in addition to 0-700m range

But, no increase in ocean heat content since 1955 in 50-60oN latitude range, especially in North Atlantic

Time-Depth Evolution of Salinity &Temperature in the central Labrador Sea

Salinity

Temperature

1000m

3000m

3000m

1000m

1975 1940 2010 I. Yashayaev

Intermittent Deep Convection cooling & freshening the intermediate layers

- greatest in 1987-1994 associated positive NAO years

- also large in late 1970s, 1950s, early 2000s

Large impact on Heat and Freshwater content of upper 2500m, and on Steric Height

OWS Bravo DFO Argo

Vertically-Averaged Temperature & Salinity Anomalies in central Lab Sea

2010 1970 1930

10-150m

20-2000m

T and S increasing in both upper 150 and 2000m since major deep convection period in early 1990s

T and S in 1960s and earlier periods comparable to those in recent years

Cooling and freshening in 1970s, 1980s and early 1990s associated with Great Salinity Anomalies (upper layer) and intermittent deep convection

Potentially misleading trends since 1980s: Natural variability vs anthropogenic change?

Hints of expected freshening: century scale and recent years in upper layer

I. Yashayaev

Central Lab Sea Temperature & Salinity Anomalies, NAO and Lab Slope T

NAO (inverted)

+

-

Warm 1960s (cold early 1990s) associated with negative (positive) NAO, but unclear for other periods

Temperature variability at 1000m on Lab Slope similar to central Lab Sea Near-bottom mooring on

AR7W Lab Slope

I. Yashayaev

Sea Level Rise

Global Mean Sea Level Rise 1880-2011: 1.7 mm/yr 1992-2011: 3.2 mm/yr

Halifax Relative Sea Level Rise

1920-2011: 3.3 mm/yr

Nearly 2x global mean

Sea Ice Area in April (HadISST)

Northern Labrador Sea, 58-63N

1900 2000 1950

I. Peterson

D. Hebert G. Han

“AMOC fingerprints” e.g. AMOC and Gulf Stream (Joyce and Zhang, 2010)

Differences in observed SST between GS South & GS North years (5 each)

Differences in GFDL model SST between elevated and reduced AMOC years

Suggestion of stronger AMOC resulting in Sward displacement of Gulf Stream, colder SST in Slope water and warmer SST in NE Atlantic.

AMO

Modes of Ocean Variability in the North Atlantic from Observations & Models Indications of inter-relations among decadal variability in the NAO and other atmospheric features, AMOC, Atlantic Multi-decadal Oscillation (AMO) and other ocean variables

Simulations with HadGEM2 ES model indicate that improved representation of aerosol-cloud microphysics can explain major fraction of multi-decadal SST variability in the North Atlantic in 20th century

2012

IPCC AR4, Ch. 10, Fig. 4.2: Multi-model means of surface warming (relative to 1980–1999) for the scenarios A2, A1B and B1, shown as continuations of the 20th-century simulation.

IPCC Scenarios IPCC Fourth Assessment Report (AR4): Emissions Scenarios (SRES)

IPCC Fifth Assessment Report (AR5): Representative Concentration Pathways (RCPs)

Projecting Ocean Climate Change in the NW Atlantic: Global Climate Models and the Challenges of Downscaling & Natural Variability

RCP8.5

RCP4.5

Sea Ice Concentration (SIC) & Sea Surface Temperature (SST) in March: Observed vs Two IPCC AR4 Models (1950-2000)

Observed Hadley CM3 CCCMA CGCM3.1

SST:

SIC:

van der Baaren

Models have too much ice in Labrador Sea & too little in Gulf St Lawrence, and Gulf Stream too far north to the west of the Grand Bank => Challenge of spatial resolution of complex ocean geometry and dynamics

February Temperature at 25 m: Observed Climatology vs 8 IPCC AR4 Models

Model Fields courtesy of B. Merryfield (CCCMA): Average of 1940-49 and 1990-99 decades Climatology from I. Yashayaev (BIO)

Broad-scale similarity in all models but significant regional differences Subtropical

water too far North off Cape Cod in all models, and not far enough in “NW Corner” in most models

Subpolar

Subtropical

Climatology

NW Corner

Cape Cod

Projected February Temperature Changes at 25m from 1990s to 2040s in 8 IPCC AR4 Models for A1B

Dark/light blue: T Decrease Red-yellow-green: T Increase

2040s: Overall warming in NWA in all models but different and complex spatial structures with large areas of cooling! Questionable whether patterns are realistic

Model Fields courtesy of B. Merryfield

Contours -1, 0, 1

van der Baaren

Projected Changes in February and August Air Temperature for RCP4.5 (left) and RCP8.5 (right) 2046-65 minus Historical 1986-2005:

Can ESM2 (Canadian Earth System Model, EC CCCMA) – a CMIP5/AR5 Model

Feb

Aug

RCP 8.5 RCP 4.5

Spatial gradients in warming over NW Atlantic, with strong winter warming over the Labrador Sea and warming band extending offshore at mid latitudes year-round

Climatologies of Sea Ice Concentration (% coverage) for Jan, March & May HadISST1 (observed) vs AR5 CanESM2 Historical

Too much ice in Labrador Sea and none in Gulf of St Lawrence Arctic Ocean, Hudson Bay and Baffin Bay are not connected in ocean model

Observed

Model

January March May

Projected Sea Ice Concentration (% coverage) in April from CanESM2

Substantial reduction in springtime extent of Sea Ice in Labrador-Newfoundland region over 60 years for both RCPs But model has different spatial pattern of sea ice extent than observed

RCP4.5

Historical 1986-2005

RCP8.5

2046-2065

Comparison of Surface Temperature & Salinity in Winter & Summer in 1946-2005 from CanESM2 Historical with Observed Climatology

Temperature Salinity

Model

Observed

Feb Feb Aug Aug

van der Baaren & Yashayaev Subtropical water too far north to west of Grand Bank, Subpolar water too far east to east of Grand Bank

Projected Changes in Surface Temperature and Salinity from CanESM2 RCP85: 2046-2065 minus 1986-2005

Feb

Aug

Temperature Salinity

Larger Temperature increases in summer (1-4oC) with maxima at mid latitudes year-round Overall Salinity decrease in subpolar gyre and Salinity increase in subtropical gyre and mid-latitude transition zone Indication of northward expansion of subtropical gyre into mid-lat transition zone But model has different representation of gyre-gyre boundary than observed

Sea Surface Height relative to the Geoid in August from CanESM2 for Historical 1986-2005 and RCP8.5 2046-2065

Bidecadal August Means

Changes in Bidecadal Aug Means (rel to 1986-2005)

Enhanced sea level rise in mid-latitude transition zone associated with northward expansion of subtropical gyre

2046-2065 1986-2005

2046-2065

Strong influences of circulation on distribution of oceanographic properties in the NW Atlantic - western boundary currents of upper-ocean gyres, AMOC and Arctic outflows

Strong decadal-scale oceanographic variability in the NW Atlantic - temperature, salinity, sea ice and circulation with broad implications - some directly related to atmospheric forcing (e.g. NAO and other), and other indirectly via ocean circulation and sea ice changes - different spatial and temporal structure north (subpolar) and west (mid-latitude transition zone) of the Grand Bank - confounds the identification of anthropogenic climate change in some variables

Anthropogenic climate change apparent in key variables (e.g. temperature, sea ice, sea level), but unclear in temperature and salinity in Labrador Sea - strong influence of decadal-scale variability in 1980s and 1990s (NAO)

Challenges for GCMs and climate change projections

Potential for enhanced climate change in some variables in mid-latitude transition zone

Summary