The basics of climate change

Thanks to our atmosphere, the climate on Earth is (on average) a balmy 59 degrees Fahrenheit. Compared to other planets in our solar system, our atmosphere is the most likely to support life (at least life as we know it). Our nearest neighbor, Mars, is closest in temperature but has an atmosphere less than 1 percent as dense and thus ranges from a chilly minus-112 to plus-23 degrees. Without our own treasured atmosphere, we'd be shivering at 5 to 22 degrees. More likely, we'd simply not exist.

Understanding how our atmosphere keeps us balmy helps us understand climate change. Solar radiation arrives from the sun and passes to the Earth's surface through the atmosphere. Much of the high-energy, destructive, short wavelength energy is absorbed by the ozone at high altitudes. This is important to us since this ultraviolet light is destructive to life.

When the incoming radiation (from visible to short energy wavelengths) reaches the earth's surface and hits a solid object, it is absorbed and converted to longer wavelength heat radiation. This heat energy is then radiated back outwards through the atmosphere. Mars is cold because its atmosphere is so thin that this heat energy is not trapped and just passes through.

Fortunately for us we have several key components at a higher density in our atmosphere, components that absorb passing radiant energy and are thus warmed. These gases include naturally occurring or human produced water vapor, carbon dioxide, methane, ozone and, less importantly, oxides of nitrogen and chlorofluorocarbons (the same gases that were, until a successful international treaty prevented it, destroying our ozone).

Not all gases occur in equal concentration in our atmosphere, and not all have the same ability to trap energy and thus warm the planet.

We often think we are very advanced compared to previous generations, and we tend to discount what they knew. But the idea that carbon dioxide might be involved in atmospheric warming — and even pose a problem — is not new. In 1896 Swedish chemist Svente Arrhenius predicted that doubling the atmospheric carbon dioxide concentration would increase the global temperature several degrees. Neither did he receive a Nobel Prize, nor did folks pay much attention, but he was way ahead of his time in accuracy.

Radiative forcing, the measure that climatologists employ to assess the role of atmospheric components, is the difference between the incoming radiation energy and the outgoing radiation energy due to a specific atmospheric component. A positive difference heats the planet, while a negative difference cools it. While joint properties of heat retention and concentration make carbon dioxide the major positive forcing agent (at 1.6), methane and oxides of nitrogen combine to produce about a 1.0 positive forcing. Aerosols (small particles in the atmosphere) then produce a negative (cooling) direct and indirect cloud albedo forcing of between 0.5 and 0.75 each. Assessing these and other minor players, the combined effect of human released atmospheric components is estimated at 1.6.

Evidence from estimators of past temperature and carbon dioxide concentration in our atmosphere indicates that for several hundred thousand years a positive correlation between these two values has existed. Though complex in its cause-and-effect relationship, the suggested pattern basically is that as carbon dioxide fluctuates so does planetary temperature.

Since the time of the Industrial Revolution (the late 1700s), fossil fuels locked in our geologic strata have been extracted and burned to produce energy to drive machines. Carbon dioxide has gradually risen from 280 parts per million to the current 370 ppm. Concurrently, the global temperature has climbed steadily — with the exception of a slight cooling period from the 1940s to 1970s when vast amounts of aerosols were being released into the atmosphere — at the rate of about one degree per century.

The problem is less what has happened in the past, although this increase has already been implicated in a number of critical biological and physical consequences, but what seems likely to happen in the future. Less than a doubling in atmospheric carbon dioxide has induced a detectable and significant increase in global temperature. But should the atmospheric carbon dioxide concentration more than double, to reach 600 ppm within this century as predictions suggest it may (absent human actions to reduce its emission), the global temperature and climatic impact could be devastating.

Certainly, it is well known that the Earth's climate has fluctuated over geologic eons, and even the last 2,000 years. However, it is generally acknowledged by experts in climatology and atmospheric sciences that the natural patterns inducing past fluctuations (e.g. solar activity and cycles in the Earth's solar orbit and tilt, which should be leading to a current planetary cooling) are not the primary current forcing factors.

The Intergovernmental Panel on Climate Change concluded not only that there is no doubt about the planet undergoing warming, but further that there is a greater than 90 percent probability that this warming is induced by humans increasing the atmospheric concentration of gases, particularly carbon dioxide. We could ignore these warnings, claiming that they are the result of a distortion of the evidence by biased researchers with some political ax to grind. But if we were to do so, it would be at our own peril, or more accurately at the peril of future generations.

Alan Journet is a co-facilitator of the Southeast Missouri Climate Protection Initiative and a professor of biology and environmental science at Southeast Missouri State University in Cape Girardeau.