02 August 2012

Global Warming Theory from David Roper

The highest form of science is measuring data to the highest accuracy possible. The lowest form of 
science is hypothesizing a model to explain the data. In between is “theory”. (“Laws” are subsets of
theories.) A theory is a hypothesis that has been shown to agree with the measured data to a high
degree of accuracy. No theory is perfect, in that it may only agree with most of the relevant data, but
not all relevant data. Often there are two competing theories over some period of time to explain a data
set; later data then can show that one theory is better than the other. Then the lesser one loses its
status as the theory for that particular set of data, but it still can be an adequate theory for a reduced
set of data. For example, Newton’s theory of motion works very well for human-scale motion, but has
been supplanted by Einstein’s theory of relativity for high speeds which has been supplanted by
relativistic quantum theory for very small objects such as atoms.
One often sees the phrase “It is just a theory.”, which is meant to denigrate a theory. Contrary to the
intention, that is high praise! If one wants to denigrate what is claimed to be a theory, one should state
“It is just a hypothesis.”.
The hypothesis of anthropogenic global warming began in 1896. (For a history of the discovery of global
warming see http://aip.org/history/climate/index.htm .) As with any scientific theory, one cannot give a
specific date when anthropogenic global warming became a theory; it was many years ago.
It is a well-established law of the theory of global warming that carbon dioxide is a major cause of global
warming. It is true that other gases contribute to anthropogenic global warming, but carbon dioxide is
the main cause. Some other gases cause more short-term global warming than does carbon dioxide, but
the longevity of carbon dioxide in the atmosphere gives it the prize. For example, water vapor is a huge
cause of global warming, but rapid precipitation removes it from the atmosphere.  And it gets there in
the first place because of the global warming caused by carbon dioxide. Methane is a powerful cause of
global warming, but its concentration is much smaller than carbon dioxide and it reacts to become
carbon dioxide and water vapor with a half-life of about a decade. (So, not putting methane into the
atmosphere would help reduce global warming, both because of it being there and because it becomes
short-lived water vapor and long-lived carbon dioxide.)
The concentration of carbon dioxide in the atmosphere is small, but it is very powerful. For example, the
Earth would be frozen if there were no carbon dioxide in the atmosphere. So, the current nearly 400
parts per million of carbon dioxide in the atmosphere does an astonishing job of keeping us warm.
Given that the current amount of carbon dioxide in the atmosphere keeps the Earth from freezing, it is
easy to realize that increasing its concentration makes the Earth warmer; it is increasing at about two
parts per million per year mostly due to humans burning fossil fuels and cutting down trees; hence,
anthropogenic global warming.

The theory of global warming is quite complex. To determine how global warming affects humans
requires complicated models incorporating the physics, chemistry and biology of the Earth. There are
many such competing models seeking to become theories. Over the last decade the many models have
converged into wide agreement on many phenomena of interest to human civilization. For example,
much sea-level rise in the future is already certain even if no more carbon dioxide were put into the
atmosphere. Also, severe storms will become the norm and increase if the amount of carbon dioxide in
the atmosphere keeps rising. Higher temperatures will put more water into the atmosphere, causing
floods in areas prone to precipitation and droughts in areas not prone to precipitation. Rapid release of
carbon dioxide and methane into the atmosphere will occur if certain triggers happen in the arctic
region, such as melting the permafrost.
All of the competing models predict that civilization is headed into a dire global-warming emergency
mainly due to burning fossil fuels and deforesting the land. The best way to mitigate the coming
emergency is to quit burning fossil fuels. Since the amount of fossil-fuels burning is directly related to
the Earth’s population, birth control becomes a moral action that humans could take.
L. David Roper, roperld@vt.edu

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