# Presentation: 513272

## IPCC (2007) and the NAS/NRC Committee on Radiative Forcing Effects on Climate

- Susan Solomon,
- co-chair, IPCC WGI
- and senior scientist, NOAA Aeronomy Laboratory

## IPCC (2001):  Houghton (UK)

- and Ding (China), co-chairs

## Time Line Issues

## What does UNFCCC want?

- Strong scientific messages telling an integrated story – not a grab bag of topics
- Clear expository graphics, avoiding “mathematical magic”
- Clear explanation of uncertainties and limits to understanding
- Address key questions
- Skip unnecessary repetition of earlier reports (very important) - this forced tough choices
- Shorter and “more focussed”

## Radiative Forcing: A key topic, as in past reports...assess anthropogenic and natural influences on radiative balance

- Review/update past and estimated future radiative forcing for greenhouse gases, and..
- ..for aerosols including indirect effects (sulfate, nitrate, organic, soot....)
- Land use/surface albedo effect
- Aviation (e.g., new studies on cloud interactions)
- Compare with natural forcings (solar, volcanic).
- Roles of short-lived vs long-lived species
- Forcing/response relations in the global mean - use and limits of the radiative forcing concept;
- GWP and other metrics for comparing emissions

## An updated and improved assessment of:•Solar•Aviation•Land use•Aerosols!• esp. soot!• Gases!•GWPs and other metrics

- An updated and improved assessment of:•Solar•Aviation•Land use•Aerosols!• esp. soot!• Gases!•GWPs and other metrics

**Joshi et al (200****3****)**

**More information on d****ependence ****of climate change ****on forcing mechanism**

## How to best convey our message?

- Many key warming agents live for decades or more

- All known cooling agents are short-lived

- AR4: stronger emphasis on timescales

## Paleoclimate:  More links to forcing	 

- Use paleoclimatic information to provide greater clarity on what may be natural versus manmade (globally and regionally)
- Illuminate key vulnerabilities to changes in radiative forcing
- Paleoclimate as a basis for testing cause and effect relationships (e.g., volcanoes and solar)
- What happened in the past and why – focus on observations and processes
- Discuss paleo measurements in greater depth - tree rings, ice cores, etc.
- More careful analysis of how anomalous the last century has been
- Review/ update what is known of abrupt climate changes – the potential wild card

## Compare to models (including volcanoes, solar, and anthropogenic forcing) for more than 1000 years

- 7 NH records

- Model with volcanoes, solar, and GHG/aerosol

- Tambora

- From Crowley, personal communication

## Couplings between changes in the climate system and biogeochemistry: “Beyond radiative forcing”

- Describe the emerging linkages in understanding and simulating the fully coupled system
- Carbon cycle / climate interactions – increasing respiration vs photosynthesis, coupling of C and N biogeochemistry, aerosol/diffuse flux linkages....
- Global atmospheric chemistry and climate change - processes influencing global ozone and methane in a coupled system, coupling of stratosphere to surface change, ....
- Air quality and climate change - interactions on new scales, where increasing numbers of people live
- Aerosols – aerosol/hydrological cycle feedbacks; regional and global scale analyses of coupled aerosol/ chemistry / climate interactions, ....
- Land surface / hydrology including e.g., fires, dynamic vegetation models
- Should better identify possible ‘wild cards’ that could emerge in an altered climate state

## One example of a coupled interaction:		

- Sea-salt emissions = function (wind speed)
- Transport (advective, convective) and deposition =function(climate)
- ==>  “in my opinion an assessment is needed in AR4” *- O. Boucher, Marrakech, 2003*

- A need to go “beyond radiative forcing” to the fully coupled system of human/climate interactions.

## Interesting new papers on aerosol forcings and responses at various levels:  A key assessment challenge for WG I

**Interesting new papers on aerosol forcings and responses at various levels:  A key assessment challenge for WG I**

- Menon et al.:  black carbon (soot) and Asian precipitation.
***How well understood are the forcings?    Surface fluxes/TOA?***

- Aerosols potentially influence precipitation at microphysical level (precipitation efficiency); sub-grid scale (altered convection); and large scale (altered circulation patterns).

- Rostayn and Lohmann:  suggesting a link of aerosols to the drought in Africa.  See also work by Rosenfeld and others on other aerosol processes that could play a role.

## Some areas of focus that this committee may wish to consider:

- Definitional issues:  How should we think about surface / tropopause / TOA forcings? What is a forcing and what is a feedback?
- Aerosols: direct and indirect effects; aerosol linkages to land use effects (e.g., biomass burning, wind stress, etc.)
- Air quality/climate: a two-way story
- Solar and volcanic forcings:  satellite era and before, including paleo.   What is a forcing and what is a feedback, across a range of time scales?

## Definitions:

**Definitions:**
**Radiative processes and their spatial distributions **

- Implications for radiative forcing?
- And the more general question:  what is a forcing and what is a feedback?

## Aerosols:  A Major Issue

- • Particle number, size, precipitation efficiency, liquid water content are all factors in climate
- • Do continental clouds have different feedbacks to aerosols than marine clouds?
- • New research on black carbon (soot) and on gradients in radiative forcing (sulfate)
- • Coupling of land use/vegetation/fires/aerosols issues

## Air Quality/Climate:  More people are living the experience

*UN, World Urbanization Prospects*
*The 2002 Revision*

## Mexico City from Satellites GOME NO2 December average

*Data courtesy J. Burrows, U. Bremen*
*Processing by S. Massie, NCAR*

## Solar Forcing:  Three full solar cycles of direct observations of the solar irradiance.  What are the constraints on solar/volcanic effects over the past three cycles, compared to human activities?

**Solar Forcing:  Three full solar cycles of direct observations of the solar irradiance.  What are the constraints on solar/volcanic effects over the past three cycles, compared to human activities?**

## Past climates: what do they tell us about radiative forcing and responses, as well as feedbacks?

- Last
- Ice
- age

- Last
- interglacial

## Concluding remarks

**• ****There are many opportunities for synergy; this presentation is a ‘sampler’.**
**• ****Timing IPCC/NRC is complementary**
**• ****Thanks for this initial discussion**