Notes Washed Up in a Bottle

Don. W. MacCorquodale M.D. M.S.P.H.

Periodic Notes From the Field on Philosophy and Science.

Global Warming

It is a riddle wrapped in a mystery inside an enigma; but perhaps there is a key. 
                                                                        - Winston Churchill
            The late Carl Sagan was one of America’s greatest scientists and a gifted writer.  In 1990 he considered the issue of global warming, and what he had to say then strikes me as the most sensible piece I have read on that matter.  What follows is taken almost entirely from his address to the American Association of Physics Teachers on the occasion of his receipt of the Oerstad Medal.
            Dr. Sagan noted that while we talk about the “ocean” of air surrounding the earth, that air is only 0.1% of the diameter of the earth, “something like the thickness of a coat of shellac on a schoolroom globe.” 
            Hundreds of thousands of years ago the population density of the earth was about a hundredth of a person per square kilometer.  Today there is an average of some ten people per square kilometer.  That we are able to alter the global environment is beyond any doubt.
            The temperature of the earth is determined almost wholly by the amount of heat that reaches our plant from the sun.  The gases in the air above us include carbon dioxide, water vapor, some oxides of nitrogen, methane, and most importantly, chlorofluoro-carbons.  This layer of stuff allows sunlight in but when it tries to radiate it back into space, it is impeded by this blanket of absorbing gases.  As a result the earth has to warm up, the “greenhouse effect.”
            As the global population increases, we pump more and more absorbing gases into the atmosphere.  There are some natural mechanisms that remove these gases, but we are producing them at such a rate that the removal mechanisms are overwhelmed. 
            The carbon dioxide mixing ratio reached 300 parts per million during the twentieth century, the highest level attained during the millennia that man has walked our earth.  The levels of methane and chlorofluorocarbons (CFC) have increased as well.  CFCs are doubly dangerous.  They attack the ozone layer, and they are greenhouse gases. 
            A number of expert groups have calculated the average increase in temperature to be about 6 to 8 degrees Fahrenheit.  There are differences of opinion.  However, Sagan pointed out that nobody contends the predictions are perfect.  The five hottest years in the 20th century occurred during the 1980s.  The warming is global.  “In the long run, there are no winners from global warming.  Everybody loses.”
            Temperature rises have effects that are very serious.  A rise in temperature of just a few degrees Centigrade by the middle of this century is predicted to cause a melting of polar and glacial ice.  The sea level will rise as a result.  Even more serious consequences may follow, including inundation of almost all of the coastal cities on earth.
            Suppose we remove a long core of ice in Antarctica or Greenland.  There are trapped bubbles of air in the ice, and we can remove the air and measure the amount of carbon dioxide.  We will find that when carbon dioxide was abundant, temperatures were higher.  When the levels were low, temperatures were low.  This is consistent with global warming. 
            Now, the most cautious projections in the middle of this century imply striking decreases in agricultural productivity because of the drought associated with global warming.  There are many nations today that cannot feed their inhabitants adequately.  The decline in agricultural production and the decreasing availability of import food subsidies might be enough to produce global famine.
            Suppose the seal level were to rise one meter.  It would inundate many small, inhabited islands, and it would prove devastating for such places as Venice, Bangkok, Egypt, New Orleans, Miami, and New York City.
            Let’s consider shared river basins, where several countries share a river.  If the water level becomes dangerously low, will there be water and food wars?  Think about Japan, which imports more than half its food.
            The biggest carbon dioxide emitter is the United States.  Hence, Sagan felt that it should bear a proportionate degree of responsibility in assuring that the problem doesn’t get worse.  The next biggest carbon dioxide emitter at the time Sagan wrote was the Soviet Union.
            Sagan offered a number of practical suggestions for dealing with climate change.  He felt that a quick phase out of CFCs, which make up about 25% of the greenhouse effect, was needed.  He added that we need much higher energy efficiencies.  “With tax relief carrots and tax penalty sticks, it should be perfectly possible to improve the efficiency of electrical power generation, make large-scale replacement of incandescent with fluorescent lamps, establish fuel efficiency for automobiles and so on . . . Why do we tolerate autos that get only 20 to 30 miles per gallon, when it is entirely feasible to manufacture autos in the 60 to 100 miles per gallon range?”
            We must make use of more renewable energy resources, particularly solar energy.  Other systems should be developed, including wind, tidal, and hydrothermal technologies.  They are renewable and nonpolluting.  Systems that burn hydrogen are possible and should be developed.  The only waste product from them is water.
            Nuclear power should be considered as a “stop-gap” between reliance on fossil fuels and new technologies.  No greenhouse gases are generated, but accidents can occur.  The “deadly witch’s brew” of radioactive elements from Chernobyl will burden our descendants for millennia to come.  (The nuclear plant at Chernobyl was a water-cooled, graphite-mediated reactor.  To the best of my knowledge, no reactors of this type are in use in the world today.) 
We need massive reforestation.  Trees remove carbon dioxide from the atmosphere.  Lumber companies must be required to plant more forests than they cut down.
            Lastly, there is another matter that is central to global warming, namely, world population growth.  People make carbon dioxide.  People have to cook, and they have to drive to work.  These activities generate greenhouse gases.  (The highly respected demographer, Joel Cohen of Rockefeller University has predicted that global population growth will stabilize by the middle of this century.  DWMac)
            There are no short-term solutions to the problem.  If we put something in the air, it stays for a long, long time.  We have no means of flushing it out.
            “Perhaps there is a silver lining to these global environmental problems. . . We know what to do.  Out of the environmental crises of our time should come, a binding up of nations and generations, and the end of our long childhood.”