Transcript document

Where do we go from here?
Bill Collins
LBL and UC Berkeley
Berkeley, California
Future work in Earth system models
• Natural and anthropogenic climate forcing
• Climate change impacts and ecosystem response
• Analytical and numerical methods for solution
• Climate and energy systems
Links between forcing and climate
IPCC AR4, 2007
Topics on forcing
• Representation of radiative forcing of the climate
• Historical & future forcings in IPCC models
(Chapter 2 and 10, WG1 AR4)
• New methods for representing radiation
Concept of radiative forcing
Radiative forcing is an “externally imposed perturbation in the
radiative energy budget of the Earth’s climate system.” (IPCC)
Historical radiative forcing
IPCC AR4, 2007
• Models should simulate this forcing as accurately as possible
• Probability that historical forcing > 0 is very likely (90%+).
• Confidence in aerosol forcing estimates is higher than in the TAR..
• The LLGHG forcing has increased by 7% to 2.59 ± 0.26 W m–2
Changes in estimates of solar forcing
IPCC AR4, 2007
Solar luminosity and sunspots
Sunspots by
Galileo
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Sunspots by
NASA
Range of future radiative forcing
IPCC AR4, 2007
Summary for longwave forcing:
• At 2000, median model & IPCC differ by only -0.13 W m-2.
• By 2100, range in forcing is 3.1 W m-2, or 47% of mean.
Summary for shortwave forcing:
• Modeled forcing spans 0 Wm-2 in every 20-year period.
• By 2100, forcing ranges from –1.7 W m–2 to +0.4 W m–2.
Range of CO2 forcing from models
IPCC AR4, 2007
• The forcing values are for 2xCO2 - 1xCO2.
• The 5 to 95% confidence interval is 3.2 to 4.1 W m-2.
• This corresponds to a 25% uncertainty in forcing.
Forcing and transmission
Atmospheric extinction causes exponential reduction in radiation fields:
Radiative fluxes and forcing involve integrals over wavelength:
Log(SW Heating Rate)
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The solar and infrared spectra exhibit variations in extinction,
optical depth, and heating rates of >10 orders of magnitude.
Robust transmission representation
Collins and Conley, 2007a,b
Effects of carbon-cycle feedbacks
Future challenges in forcing
• A global model for the sun and its luminosity
• Better mathematical representations of radiation
• Natural and anthropogenic feedbacks on forcing
• Equivalence of Maxwell’s and transport equations
Climate change impacts
• Natural and anthropogenic climate forcing
• Climate change impacts and ecosystem response
— Short-range climate forecasts
— Predicting tropical cyclone activity
• Analytical and numerical methods for solution
• Climate and energy systems
Projections for global surface temperature
Meehl et al, 2005
• Between 50 to 70% of warming in 2050 relative to pre-industrial periods Is “committed”.
• Therefore the short-range predictions are relatively insensitive to socioeconomic scenarios.
Climate change: decadal time-scales
Transient climate response vs.
Equilibrated climate sensitivity
IPCC TAR, 2001
• The range of transient response is 3X smaller than the equilibrated sensitivity.
• Therefore the multi-model set of short-term predictions should be more consistent.
Schema for short-range prediction
Step 1: Quantify prediction errors using hindcasting
Assimilation
Phase
30 years
Assimilation
Phase
Prediction
Verification
30 years
Prediction
Verification
30 years
Assimilation
Phase
Prediction
Verification
Step 2: Ensemble prediction of near-term climate change
Assimilation
Phase
Climate
Prediction
Step 3: Downscaling for regional and national forecasts
Climate
Prediction
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1960
1970
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1990
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2010
2020
2030
Regional
Climate Models
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2050
Nested regional climate modeling
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Scientific motivation:
— At current resolutions of global models, we cannot resolve
cloud evolution and convective mixing of the atmosphere.
— Does resolution of these processes affect climate-change simulations?
— How do these processes affect regional impacts of climate change?
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Intermediate solution: regional climate models
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Models are limited in domain.
Integrations are limited in length (< 1 decade).
Simulations are “snap shots” of current or future climate.
These models could eventually be nested in global models.
Our first experiments are designed to:
— Determine the climate of high-resolution regional models.
— Evaluate the fidelity in stratus regions, tropical western Pacific, etc.
Nested regional climate configuration
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• Base model: NCAR Advanced Research version of WRF
• Meridional boundaries at 35S/45N are relaxed to NCEP reanalysis.
• 4 km and 12km grids nested in 36km outer grid.
• Kain-Fritsch cumulus scheme is used on 12 and 36km grids.
• Period of integration: Jan. 1, 1996 to Jan. 1, 2001
NRCM tropical cyclone simulation
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NIO NRCM
NIO OBS
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Number of TCs
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Observed
ENP NRCM
ENP OBS
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Challenges in climate impacts
• Theory for signal to noise for short-range prediction
• Information gain with resolution?
• Feedbacks from non-linear local phenomena,
e.g. from cyclones
• Theory linking climate response to observables