Facts of the Matter
Various factors correlate with climate change
There is little doubt that the globe has warmed in the past 125 years. The standard that tracks global temperature changes is the global temperature anomaly (GTA), an average of how much global temperatures have differed from the 1951-1980 average. The National Climate Data Center determined it by processing data from thousands of surface air and sea surface temperature measurements taken since 1880.
Today, Earth overall is warmer than the GTA by just over 1 degree Fahrenheit, and about 1 1/2 degrees warmer than in 1880.
Computerized climate models rely heavily on carbon dioxide levels in their predictions, and since 1880 carbon dioxide levels have increased by nearly 35 percent. On the other hand, Earth's average temperature has fluctuated over a range of about 5 1/2 degrees during the past 3,000 years, while carbon dioxide levels decreased rather steadily.
There is a nearly 1-to-1 correlation between carbon dioxide and temperature only for the past 450,000 years during the extremes of the ice age, but the correlation is much weaker for other stretches of geologic time.
Furthermore, carbon dioxide is not the only factor that correlates with climate change, and it is not the sole determinant of Earth's temperature.
Solar activity actually correlates better with temperature fluctuations than with carbon dioxide emissions over the 125-year period of the GTA data. Increased solar output brings more UV radiation that increases ozone, which is also a greenhouse gas. Changes in solar activity also change Earth's magnetic field and interfere with the west-to-east circulation of the atmosphere that drives the swirling air masses of winter storms and hurricanes.
Water vapor, which is thousands of times more abundant in the atmosphere than carbon dioxide, is a significant greenhouse gas, with 80 times the power of carbon dioxide. Cloud cover counterbalances the effect of water vapor since higher humidity results in more clouds that reflect the light that is ultimately responsible for Earth's temperature. Yet a reduction of only 2 percent in overall cloud cover would reduce Earth's temperature to pre-industrial levels.
Cosmic ray activity might even be a factor by acting as seed particles for cloud formation. One study found correlations between electromagnetic induction at the boundary between Earth's core and mantle, which causes torque between the mantle and core that in turn alters Earth's rotation rate and affects weather.
This same study found that carbon dioxide levels lag the GTA on several time scales. If it were a driving factor in global warming, carbon dioxide levels would lead rather than lag the GTA.
There is little doubt that human activities have contributed to the buildup of carbon dioxide and that there is a correlation between carbon dioxide and temperature in geologically recent times, but correlation does not imply causality and there is no evidence that one causes the other.
There is a real danger that the politicalization of current global warming science could dissuade researchers from seeking grants in favor of going where the money is or from studying other factors for fear of damaging their reputations.
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