Monday, January 21, 2008
The physics behind global warming
From the RoundTable blog
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L. David Roper
Roper, who lives in Blacksburg, is professor emeritus of physics at Virginia Tech.
The science of carbon dioxide in the atmosphere serving as a greenhouse gas was well established by Svante Arrhenius in 1896, so there is no valid argument that carbon dioxide in the atmosphere does not cause global warming. It has become well established that other gases, such as methane, in the atmosphere also are greenhouse gases.
Particulates in the atmosphere cause what is called global dimming. The Earth-temperature record since 1850 clearly shows two periods (1880-1910 and 1940-1980) of global dimming due to particulate pollution by burning coal and oil until it was reduced because of health problems it was causing.
For the first period, global dimming was greater than global warming, causing the Earth temperature to decrease for about three decades, and for the second period global warming and global dimming were about equal, such that the temperature remained almost constant for about three decades.
After 1980 the rapid rise in temperature due to global warming became dominant, leading to the extreme melting of Arctic and Antarctic ice and rising ocean level that is happening today. (Some are proposing putting pollutants into the atmosphere in the future to counter global warming with global dimming.)
What will be the future of global warming? Some have predicted that global warming will continue to increase indefinitely. That is not correct because of the finite supplies of oil, natural gas and coal.
Oil extraction is at or very near peaking. Natural gas extraction will peak at about year 2010 and coal extraction will peak between 2050 and 2100. These three fossil fuels are the major sources of carbon dioxide put into the atmosphere.
Other sources of carbon dioxide in the atmosphere, such as deforestation, are related to how fast population is growing. Fortunately, world population growth is slowing down and probably will stop growing within the next century. So, carbon dioxide insertion into the atmosphere due to population change will peak and then decline.
The result of fossil fuels and population growth peaking is that the amount of carbon dioxide being put into the atmosphere will peak. I have done a calculation taking those four peaks into account and have concluded that the carbon dioxide concentration in the atmosphere will go from its present value of about 385 parts per million to a peak of about 450 parts per million at about year 2100 and then will decline to about the same value as now for several centuries. Climatologists estimate that atmospheric concentration over 400 ppm will cause many disasters for humans on the Earth.
So, carbon dioxide in the atmosphere will not increase indefinitely, which is good news. But there is no reason for celebration because already, at 385 ppm, disastrous things are happening. Also, on the way to 450 ppm it is difficult to predict with assurance what other disasters will occur, but we can be sure that some will. One possibility that may greatly increase global warming, that seems to be already under way, is the release of massive amounts of carbon that is frozen in the Arctic tundra.
I have done a calculation that assumes that a large amount is released into the atmosphere (200 gigatonnes) over a 200-year period with a peak at year 2100. The result is that carbon dioxide in the atmosphere would peak at about 535 ppm at about year 2135 -- a truly disastrous value. And then it falls to about 420 ppm for several centuries, still in the disaster zone.
All of the discussion above assumes that humans will continue to extract oil, natural gas and coal as fast as possible and burn about 75 percent of it as fuel and that population will continue to grow to about 8.5 billion.
Is it possible for human society to realize the dangers of burning fossil fuels so quickly and not saving more of it for making useful materials and for future generations? I and many others are working hard to make that happen.
Many are touting uranium as a carbon-free source of energy, albeit a finite source. It is not carbon free and a recent study has shown that uranium will never be able to come close to filling the energy gap after fossil-fuels extraction peaks and then declines. Will humans devote massive amounts of fossil fuels to developing nuclear reactors instead of developing renewable sources of energy?
