# Presentation: 907681

## What Do Climate Models Require from Aerosol Researchers: My Views

- Warren M. Washington
- National Center for Atmospheric Research
- Boulder, Colorado
- October 2005

## Outline of Talk

- My perspective will be on the 20th and 21st century climate change.
- What is in the Community Climate System Model (CCSM) with respect treatment of aerosols?
- How can the aerosol community help make climate model aerosol effects better?

## Timeline of Climate Model Development

## Horizontal Grid Resolutions

-  (300 km)

-  (150 km)

- (75) km

-  (37 km)

- Next IPCC

## Chemistry Interactions in CCSM

- From Bill Collins

## Shortwave Formulation in Standard CCSM

- -Eddington, solar spectrum divided in 19 spectral intervals, 1 visible, 7 H2O, 3 CO2, 1 near infrared, 7 in UV for ozone heating (Collins et al.,1998)
- Molecular scattering, scattering and absorption by cloud droplets and aerosol included
- Aerosol species-3D time dependent distribution: sea salt, soil dust, carbonaceous, sulfate, volcanic sulfuric acid
- Method allows for both direct and indirect effects. Most simulations have indirect turned off. e.g. IPCC simulations...why...uncertainties!

## More 

- Three optical properties for each aerosol type: specific extinction, single scattering albedo, and an asymmetry parameter.
- Hygroscopic growth included.
- More details are included in http://www.ccsm.ucar.edu/models/atm-cam/docs/description/

## Some Numerical Details with Respect to Aerosol Transport

- Finite volume transport approach which is volume conservative and positive definite...not trouble free; e.g. requires polar smoothing, may be too diffusive. Key is transport the plumes more accurately both vertically and horizontally. Connection to ARM.
- Note the difference between conservation and transport accuracy! This presents a serious problem because aerosol properties evolve in the process of transport.

## Title slide

- Mt Pinatubo eruption in the Philippines, June 15, 1991.  Gases and solids injected 20 km into the stratosphere.

- From Church, White, & Arblaster

## Slide 10

## Krakatau (1883)

- Sometimes
- referred
- to as Krakatoa

## PCM:       2XCO2 = 2.1°C       TCR = 1.32°C

- PCM:       2XCO2 = 2.1°C       TCR = 1.32°C
- CCSM3:  2XCO2 = 2.7°C      TCR = 1.46°C

## Sulfate (direct effect)

- Sulfate (direct effect)

## Change of Extremes

- Heat waves, cold snaps
- Floods, droughts
- First freeze dates, hard freeze frequency
- Precipitation intensity
- Diurnal temperature

- Note all of these are sensitive to regional
- aspects of aerosol distribution

## CCSM Climate Change Working Group Plans, 2005-2006

- Analyses of climate sensitivity
- Large ensembles and climate change signals (collaborate with CVWG)
**Address role of aerosols in 20****th**** century and future climate change (e.g. sulfate direct and indirect, dust, black carbon, etc.)**
**Determine respective roles of natural forcing ( solar and volcanic) and anthropogenic forcing (changes in GHGs, aerosols;  also land use/land cover change (LULCC)—collaborate with LMWG) **

## 2006-2008:

- Quantify possible sea level rise scenarios based on hypotheses of ice sheet de-stabilization (include dynamic ice sheet model)
**Perform targeted climate change mitigation/adaptation simulations with CCSM3 with coupled carbon cycle (collaborate with BGCWG and LMWG); initial use of WG3 scenarios to precede fully coupled carbon cycle**

## More on CCSM Radiation Physics

- Cloud geometrical overlap
- New water vapor treatment
- Prognostic sulfur cycle for prediction of sulfate aerosols...this is in reasonably good shape.
- Prescribed distribution of sulfate, soil dust, carbonaceous species, sea salt for direct effects on radiative fluxes and heating rates
- Volcanic aerosols
- Indirect effects of aerosols on cloud albedo and cloud lifetime are not yet included in CAM3.

## What Do We Need From the Aerosol Community?

- Better observational based parameterizations of optical depths of specific aerosols. (Is what we are using the best?)
- MODIS and other satellite system are valuable instruments but it has problems with uncertainties in several areas: contamination clouds and over various surfaces, accuracy degrades with high and low optical depths, need for more in situ validation, sun glint, etc. The data we can use is mostly totals...but we are happy with it.
- How should we deal with various size distributions? i.e. is the log normal good enough? Or should we go with, say, 10 size ranges in a grid cell?
- Do we have enough solar bands?
- Methods for incorporating indirect effects.

## More

- Uncertainties in emissions, especially carbon aerosols-anthropogenic, biomass burning...lighting caused forest fires. Models tend give low concentrations...compared to observations...reason not known. (Rasch,2005)
- Removal mechanisms are 20 years old...are there new parameterizations coming out future research? (Rasch, 2005)

## More

- If possible, we need more computationally efficient parameterizations (i.e. stop using those exponents and power approximations when table lookup or series approximations will do). However, real computational cost is the transport of aerosols and associated chemistry.

## Sulfate

- Mineral Dust

- Sea Salt

- Organic and Black
-        Carbon

- Industrial sulfur
- emissions

- Mostly near the
- Sahara

- Near strong
- wind areas

- Biomass
- burning

- From Bill Collins et al

- Optical Depths base on aerosol chemistry transport model

## Clear Sky Only (W/m2)

- Top of Atmosphere

- Surface

- Atmosphere

- Clear Sky Only (W/m2)

## What types of aerosol observations do we need?

- Surface, aircraft, and satellite (What is DOE’s role? Is it to integrate the various sources?)
- MODIS clear sky observations TOA forcing and other details on amount and type of aerosols
- Use satellite spectral dependence of cloud reflectivity to obtain effective radius of clouds droplets...tie to indirect effect.

## Are we heading down a slippery road of increased complexity?

- Computer capability will increase by factors of five every two years or so. This limits climate model and BGC complexity!
- How many species should be keep track of in a climate model?
- What does DOE want special emphasis on? e.g. carbon cycle, effects of carbon and sulfate aerosols from fossil fuel use, etc. To sort out role of carbon we need all major aerosol types.

## The Next IPCC Simulations (1870-2100)

- Some moderate resolution climate model simulations with fully interactive BGC model, with emphasis on carbon cycle and aerosols. Note this should be DOE priority.
- Higher resolution (T170) simulations  with specified or transport BGC but no feedback on climate system
- Scenarios need improved treatment of aerosols for 20th century and prediction of future emissions or concentrations.

## The End