INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (IPCC) Working Group I

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

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IPCC (2001): Houghton (UK)and Ding (China), co-chairs

Climate Change 2007 The Physical Science Basis

IPCC (2007): Solomon (USA) and Qin (China), co-chairs

An NRC report that was an important input to the TAR

This committee: an important opportunity for similar synergy through dialogue

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Time Line Issues

WGI panelJan 2007

Lead Author meeting 4 (TBD)Jun 2006

Second draft completeFeb 2006

Lead Author meeting 3 (Christchurch)Dec 2005

First draft completeAug 2005

Lead Author meeting 2 (Beijing)May 2005

Second scoping meeting Sep 2003

Zero order draft completeFeb 2005

Lead Author meeting 1 (Trieste)Sep 2004

Lead author teams selected by WGI BureauApr 2004

Panel approval of outlines for reportsNov 2003

First scoping meetingApr 2003We are here:

the outline is in final form and is about to be submitted to the Plenary for approval

This committee’s report is due just before WGI authors begin first formal draft

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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”

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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

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CO2 Solar UT O3

LS

O3

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

Joshi et al (2003)

More information on dependence of climate change

on forcing mechanism

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How to best convey our message?

Many key

warming agents

live for decades or more

All known coolin

g agents

are short-lived

AR4: stronger emphasis on timescales

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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

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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

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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

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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.

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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.

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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?

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Top-of-the-atmosphere Surface (Wm-2)

March 97

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?

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• 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

Aerosols: A Major Issue

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UN, World Urbanization ProspectsThe 2002 Revision

Air Quality/Climate: More people are living the experience

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Mexico City from Satellites GOME NO2 December average

Data courtesy J. Burrows, U. BremenProcessing by S. Massie, NCAR

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FAR SAR TAR AR4

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?

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QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

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

Last Ice age

Lastinterglacial

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Concluding remarks

• There are many opportunities for synergy; this presentation is a ‘sampler’.

• Timing IPCC/NRC is complementary

• Thanks for this initial discussion