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  1. VTT WORKSHOP: PANEL 5(10/29/03)[Wigley, Forest, Groisman, Pielke, Robock,Thorne]“How well can the observed (vertical temperature profile) changes be reconciled with our understanding of the causes of (these) temperature changes?”“(Do our attempts to reconcile these changes) increase or decrease our confidence (in explaining and quantifying) the human impact on (past and future) climate changes?”

  2. ISSUE: What is meant by ‘reconcile’?Reconciliation requires that we can both detect a statistically unusual change and attribute these changes to particular causes, both human induced and natural (cf. ‘discernable human impact’).Reconciliation means that there are no differences between observed changes and model expectations that cannot be explained within forcing, model structure, observational and statistical uncertainties.

  3. CAUSES OF CLIMATE CHANGE (since 1978): i.e., external forcing factors(1) Solar irradiance changes*(2) Volcanic eruptions*(3) Well-mixed greenhouse gases*(4) Tropospheric ozone(5) Sulfate aerosols(6) Other aerosols and trace gases(7) Land-use and vegetation changes(8) Stratospheric ozone*[* denotes adequately considered in climate model simulations; where ‘adequately’ means that the uncertainty associated with the factor is small]e

  4. AREAS OF REASONABLE ‘AGREEMENT’ BETWEEN MODELS AND OBSERVATIONS*(1) Global-mean surface warming (since 1978)(2) Surface temperature change patterns (1976-1999)(3) Changes in lapse rates in mid latitudes (but not for all tropospheric data sets)(4) Stratospheric cooling (global mean and pattern)(5) Changes in the height of the tropopause (indirect evidence of stratospheric cooling and, possibly, tropospheric warming) * Note that there is uncertainty because not all potentially important forcing factors have been included in model simulations

  5. AREAS OF DISAGREEMENT(1) Changes in lapse rates in the tropics (surface warming and tropospheric cooling in many data sets)(2) Changes in lapse rates in extra-tropics (with some data sets)

  6. POSSIBLE REASONS FOR DISAGREEMENTS(1) Data uncertainties associated with coverage, spatial representativeness, and instrumentation changes(2) Decoupling of surface and troposphere in the subtropics (TWI)(3) Deficiencies in modeling convection(4) Diurnal cycle changes in midlatitudes(5) Signal-to-noise considerations (do differences reflect noise or a signal ‘error’?)(6) Deficiencies in representing forcings

  7. “(Do our attempts to reconcile these changes) increase or decrease our confidence (in explaining and quantifying) the human impact on (past and future) climate changes?”(1) Increasing observational uncertainty removes some model/data inconsistencies(2) Increasing recognition of the complexity of the climate system must increase uncertainties in future projections(3) Improving our understanding of VTT since1978 will increase our confidence in models, but will not reduce uncertainty in estimates of the climate sensitivity* and the rate of ocean heat uptake.*Need to define term(s)

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