Research Needs for Decadal to Centennial Climate Prediction: From observations to modelling

Julia Slingo, Met Office, Exeter, UK

&

V. Ramaswamy. GFDL, Princeton, USA

Climate Change Projections and Uncertainties

IPCC AR4

931

2535

Natural Variability Carbon Cycle

Downscaling Model Uncertainty

15

20

43

22

2020’s 2080’sWinter rainfall in south east

EnglandImproved model physics e.g.

clouds

Increased understanding of earth

system processes – more uncertainty?

Benefits of initialisation for near-

term projections

Quantifying uncertainties – setting research priorities

Higher resolution global

models

Challenges for Centennial Projections:

Earth System Modelling

Land physicsand hydrologyOcean circulation

Atmospheric circulation and radiation

Land physicsand hydrology

Ocean ecology andbiogeochemistry

Atmospheric circulation and radiationAllows interactive CO2

Ocean circulation

Plant ecology andland use

Climate Model

Earth System Model

Sea Ice

Sea Ice

Moving from Climate to Earth System Models: Balancing the carbon cycle

Carbon-climate feedback and centennial climate change

More Earth System Modelling challenges

• How can we reduce the uncertainties in current estimates of the carbon-climate feedback?

• How do missing or poorly represented processes such as the nitrogen cycle, plant adaptation to climate change, vegetation dynamics, and plankton dynamics affect current model results?

• What other biogeochemical feedbacks involving methane, ozone and aerosols play a significant role on the centennial timescale?

• How can Earth System Modelling inform decision-making when climate change is one of many drivers for environmental change (e.g. food security, water resources and quality, biodiversity, air quality)?

Earth System Modelling:Combining the needs of adaptation and mitigation

931

2535

Natural Variability Carbon Cycle

Downscaling Model Uncertainty

15

20

43

22

2020’s 2080’sWinter rainfall in south east

EnglandImproved model physics e.g.

clouds

Increased understanding of earth

system processes – more uncertainty?

Benefits of initialisation for near-

term projections

Quantifying uncertainties – setting research priorities

Higher resolution global

models

Challenges for Decadal Prediction:

Initialisation and Evaluation

Decadal predictions of global annual mean surface temperature

Observations

Forecast/hindcast

Forecast from 2008

Forecast from 2009

Smith et al., 2007

Impact of initialisation on hindcast skill5 year mean (JJASON) surface temp

15x15 degrees

DePreSys-NoAssim correlationDePreSys anomaly correlation

• HadCM3

• 9 member perturbed physics ensemble

• Starting every Nov from 1960 to 2005

Improved predictions of multi-year Atlantic hurricane frequencies

Nor

mal

ised

ano

mal

y

DePreSys NoAssim

5-year mean JJASON number of model storms (coloured) and observed hurricanes (black)

Skill comes from SSTs in tropical Pacific and N. Atlantic sub-polar gyres, and from wind shear in hurricane development

regions

Sub-surface ocean observations: A limiting factor in estimating skill and predictability

19801960 2007

• Need historical tests to assess likely skill of forecasts

• Far fewer sub-surface ocean observations in the past

Doug Smith, Met Office Hadley Centre

Temperature at 300m : June 2007 from 1960 observational base

Analysis using all obs Analysis using sub-sampled (1960) obs

June 2007 obs June 1960 obs

Variability versus Anthropogenic Forcing of

the Physical Climate System

20 centuries of NINO3 SSTsannual means & 20yr low-pass

Major uncertainty in Chemistry-Climate

Interactions

LandOceanSea Ice

Mixed-Layer

Deep Ocean

SST

Surface Flux

Clear Sky Cloudy Sky

Aerosols DropletsActivation

SW Radiation

LW RadiationEvaporation Precipitation

Atmosphere

Coupled Chemistry-Aerosol-Climate model

Aerosols and Climate

Global Air Quality and Climate

Aerosol-Cloud Interactions in GFDL’s Newest Physical Climate Model (CM3)

20

CM3 CM2.1

Direct effects – Sulfate and organic carbon

~0

(assuming internal mixing of sulfate and black carbon)

-1.3

(external mixing)

Direct effects - Black carbon

0.5

(external mixing)

Indirect effects -1.3 Not included

Radiative Flux Perturbation w/m2

Comparison of Simulated Aerosol Properties with Observations

Observations (AERONET)

Observations (AERONET)

MODEL

MODEL

Capturing High-Resolution Phenomena

Atlantic Hurricanes in a Warming World

Most recent GFDL downscaling study (Bender et al, Science, 2010) see https://www.gfdl.noaa.gov/21st-century-projections-of-intense-hurricanes

Uses two downscaling steps: Global CMIP3 models => regional model of Atlantic hurricane season regional model => operational GFDL hurricane prediction system

Conclusion: Best estimate is for doubling of cat 4-5 storms in Atlantic by end of century, despite decrease in total number of tropical cyclonesMuch of the uncertainty arises from global model input

Conclusions I

• Emerging need for centennial and decadal projections. They pose similar and differing challenges.

• Earth system processes potentially increase uncertainty in centennial projections, especially in the upper range of warming.

• Initialising decadal projections can reduce uncertainty at least for a few years ahead.

Conclusions II

• Observations of the sub-surface ocean and the full earth system may limit our ability to provide more confident projections.

• Natural variability in the context of forced change is challenging.

• High resolution modelling is opening up new avenues for more detailed projections of regional climate change and high impact phenomena.