Facts of the Matter
Science looks for answers on Earth’s climate
If you have the feeling that scientists can't make up their minds you are correct. If they refused to change their minds they would not be scientists because scientific "belief" is of a different form of belief than we commonly infer.
Science is the search for physical truth, based on verifiable facts. Theories are tested but tentative explanations, based on assembling facts in the most parsimonious and most consistent way with the fewest contradictions.
Science is verifiable, repeatable and falsifiable but does not rely on proof. Instead, scientists try to disprove theories. Theories that resist repeated attempts to disprove them become stronger with each failure.
Skepticism is the strength of science since no theory that contradicts facts will be accepted, although new facts may validate ideas that were once rejected.
Causality is a recurring problem when studying complex systems such as the earth. Relationships do not necessarily mean that one thing is the cause or the control of another.
Global temperature increases may be concomitant with increases in atmospheric carbon dioxide, but fluctuations have always been a natural part of Earth's attempts at homeostasis.
Carbon dioxide has risen 20 percent in the past 50 years, and this correlates very tightly with the rise in average global temperature. However, the change is slightly less than 1 degree Fahrenheit when compared to the global average temperature from 1951-1980 of 57.2 degrees.
Comparing human-scale, short-term changes with short-term averages does not mean much. Temperature fluctuations over the past 3,000 years paint a very different picture.
In 1000 B.C., Earth's temperature was 62 degrees F. It reached a low of 55 degrees around 200 A.D. After that, it rose bumpily to the Medieval climate optimum of 60 degrees around 1000 A.D., nurturing a rich food supply and a sociology of serfdom in temperate climates.
When temperatures began to fall around 1200 A.D., there were extensive crop failures, pestilence, and territorial aggression. By 1500 Earth's temperature had climbed again to 58 degrees, about the same as now.
The "little ice age" refers to a severe temperature drop over 200 years, during which temperatures fell to a low of 55 degrees by 1700. So severe was the weather that priests traveled en masse to exorcise advancing glaciers in Alpine valleys.
Since 1880, temperature correlates much more with solar activity than with any other variable, and there is increasing interest in the sun as a major factor in climate change.
Temperatures increased for a century before hydrocarbon use spewed carbon dioxide, and continued to rise between 1910 and 1940 while hydrocarbon use remained nearly constant.
Throughout most of Earth's history its temperature has been much warmer than now, and there have been periods of extraordinarily high carbon dioxide concentrations. Yet there is little correlation between temperature and atmospheric carbon dioxide in the geological past.
Temperature and atmospheric carbon dioxide are both increasing, but whether there is cause-and-effect relationship, and if so which is cause and which is effect, are questions that are a long ways from definitive answers.
Richard Brill, professor of science at Honolulu Community College, teaches earth and physical science and investigates life and the universe. E-mail questions and comments to firstname.lastname@example.org