Day 011 - 12 Jul 94 - Page 27


     
     1         ---"  I think perhaps we do not need to bother about
              that. So far as it goes, apart from the bit you mentioned
     2        about heat absorption, is that a fair summary of the
              scientific knowledge on the subject at that time?
     3        A.   One could even say that for the heat absorption it
              was a reasonable account because the infra red spectra of
     4        those compounds had not been properly documented at the
              time that report was produced.
     5
         Q.   Can we go back to the SORG report for August 1987?
     6
                                 (Short adjournment)
     7
         MR. RAMPTON:  Professor Duxbury, do you have still open the
     8        executive summary of the SORG report for 1987?
              A.   I do.
     9
         Q.   I had got to just below half way in the second column on
    10        page 377.  I will go on, if I may.
 
    11         "The lifetime of CFCs in the atmosphere is about 100
              years.  Any changes in stratospheric ozone brought about
    12        CFCs will be long- lived.  Model predictions show that in
              the hypothetical case of a complete cessation of CFC
    13        emissions ozone will be continue to decline slightly for a
              further 5-10 years before recovery begins ---"
    14
              Will the ozone layer recover if we stop emitting these
    15        substances into the atmosphere?
              A.   It is believed that it will.
    16
         Q.   "But the additional depletion will be less that one per
    17        cent.  The overshoot will be greater, and the recovery
              time longer, if CFC emissions are reduced rather than
    18        terminated completely.  These predictions depends
              critically on assumptions of changes in other source
    19        gases, particularly methane."
 
    20        Can you explain why changes in other source gases,
              particularly methane, might affect the assumptions?
    21        A.   The main comment I would make is that this is the
              knowledge in 1987.
    22
         Q.   I agree.
    23        A.   I don't think, in the current circumstances, people
              would actually attribute in the stratosphere the weight to
    24        methane that the panel gave in 1987.
 
    25   Q.   Perhaps we can leave it there.  I will read on,  "All the
              source gases which influence ozone concentrations are also 
    26        greenhouse gases, as is ozone itself in the troposphere. 
              Rising concentrations of these gases are expected to lead 
    27        to an increase in the surface air temperature- the 'global
              warming'.  Current models, assuming continued growth in
    28        concentrations of greenhouse gases for the next 50 years,
              estimate a global temperature rise of between 1.5 and 4.5
    29        degrees celsius.  There are large uncertainties in this
              estimate.  Moreover the realisation of this warming may be
    30        delayed by decades due to the thermal inertia of the
              oceans."

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