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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties

Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties. Report from the NRC Committee on Radiative Forcing of Climate released December 2004. Committee on Radiative Forcing of Climate. DANIEL J. JACOB ( Chair ) , Harvard University

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Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties

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  1. Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties Report from the NRC Committee on Radiative Forcing of Climate released December 2004

  2. Committee on Radiative Forcing of Climate DANIEL J. JACOB (Chair), Harvard University RONI AVISSAR, Duke University, GERARD C. BOND, Lamont-Doherty Earth Observatory STUART GAFFIN, Columbia University JEFFREY T. KIEHL, National Center for Atmospheric Research JUDITH L. LEAN, Naval Research Laboratory ULRIKE LOHMANN, Dalhousie University MICHAEL E. MANN, University of Virginia ROGER A. PIELKE, SR., Colorado State University VEERABHADRAN RAMANATHAN, Scripps Institution of Oceanography LYNN M. RUSSELL, Scripps Institution of Oceanography

  3. Conceptual framework of climate forcing, response, and feedbacks • CLIMATE FORCING AGENTS • Emissions of greenhouse gases and precursors, aerosols and precursors, and biogeochemically active gases • Solar irradiance and insolation changes • Land-cover changes NATURAL PROCESSES Sun, orbit, volcanoes • HUMAN • ACTIVITIES Fuel, industry, agriculture… Non-radiative Forcing • CHANGE IN CLIMATE SYSTEM COMPONENTS • Atm. lapse rate • Atm. composition • Evapotranspiration Direct Radiative Forcing Societal Impacts Indirect Radiative Forcing Feedbacks CLIMATE RESPONSE Temperature, precipitation, vegetation, etc.

  4. Climate change research and policy has relied on global top-of-atmosphere (TOA) radiative forcing TOA forcing from 1750 to present [IPCC, 2001]

  5. Strengths and limitationsof TOA radiative forcing concept The TOA radiative forcing concept should be retained and expanded

  6. Account for vertical structure of radiative forcing The relationship between TOA radiative forcing and surface temperature is affected by the vertical distribution of forcing within the atmosphere, particularly for absorbing aerosols and for land-use driven changes in evapotranspiration. • Test ability of climate models to reproduce observed vertical structure of forcing; • Characterize dependence of climate response on the vertical structure of radiative forcing;. • Report global mean radiative forcing at both the surface and the TOA in climate change assessments; • .Develop practical tools for incorporating surface radiative forcing in policy analyses and integrated assessment models. Aerosol radiative forcing Priority recommendations:

  7. Determine the importance of regional variation in radiative forcing Regional variations in radiative forcing may have important regional and global climatic implications that are not resolved by the concept of global mean radiative forcing. • Quantify and compare climate responses from regional radiative forcings in different climate models, and report results in climate change assessments; • Use climate records to investigate relationships between regional radiative forcing and climate response. JJA forcing by tropospheric ozone Priority recommendations:

  8. Determine the importance of non-radiative forcings Several types of forcings—most notably aerosols, land-use and land-cover change, and modifications to biogeochemistry—impact the climate system in non-radiative ways, in particular by modifying the hydrological cycle and vegetation dynamics. Historical changes in land cover • Improve understanding and parameterizations of aerosol-cloud thermodynamic interactions and land-atmosphere interactions in climate models; • Develop improved land-use and land-cover classifications at high resolution for the past and present, as well as scenarios for the future. 1700 Priority recommendations: 1900 1990

  9. Addressing Key Uncertainties 1. Conduct accurate long-term monitoring of radiative forcing variables Spectrally resolved radiances from space, ocean heat content… 2. Advance the attribution of decadal to centennial climate change Mine climate forcing and trend records for past 1000 years 3, Reduce uncertainties associated with indirect aerosol radiative forcing Improve parameterizations used in models 4, Better quantify the direct radiative effects of aerosols Improve understanding of aerosol sources, mixing states, sinks 5. Better quantify radiative forcing by ozone Improve understanding of strat-trop exchange, lightning NOx 6, Integrate climate forcing criteria in environmental policy analysis Examine climate impacts of policies directed at air quality and land use, develop GWPs for short-lived agents, determine additivities of forcings,,,

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