Burning fossil fuels has been cited as contributing to the greenhouse effect and potentially causing global warming. The greenhouse effect controls the temperature of the earths surface. Incoming radiation from the sun is in the short wavelength, visible and ultraviolet portion of the electromagnetic spectrum. This energy is absorbed by the earths surface and radiated back as longer wavelength, infrared radiation. The greenhouse gasses of the atmosphere allow visible and ultraviolet radiation to pass through but absorb infrared radiation. This absorbed radiation increases the temperature of the earths surface. Currently there is a balance between the amount of energy absorbed from the sun and the amount radiated back into space. If the amount of greenhouse gasses increases it could disturb this balance by increasing the greenhouse effect.
The major greenhouse gasses are water and carbon dioxide, which are capable of absorbing infrared radiation. In addition methane, nitrous oxide and ozone contribute to the greenhouse effect.
Evidence suggest that the level of carbon dioxide in the atmosphere has been rising. This graph shows the level of CO2 in the atmosphere measured at Mauna Loa Hawaii. Mauna Loa was selected because it is a remote area removed from the influence of major cities and is believed to be representative of the average CO2 for the earth.
Another way to estimate the increase in CO2 in the atmosphere is to calculate CO2 emission based on past fossil fuel consumption. This graph shows that CO2 emissions have been rising since the late 1800s and coal is the major contributor of CO2 to the atmosphere. This graph only shows emissions up to 1940, since then our oil consumption has increased and coal has decreased. A similar calculation for modern day emissions would show a greater contribution from oil and less from coal.
The graph of the global temperature anomaly indicates that the temperature has increased 0.5 degrees C since the middle of the 19th century. The global temperature anomaly is calculated from the average annual temperature of a number of sites around the world. There are still a number of questions that need to be answered about the relationship between burning fossil fuels, the greenhouse effect, and global warming. Is the rise in temperature we observe during the past 100 years a natural phenomena or induced by mans activities? How much excess CO2 can the atmosphere absorb before there is a significant climatic effect? Are climate changes gradual or instantaneous. Answers to these and other questions can be obtained by studying the geologic record and climate changes of the past.