Heating the Earth - Most heat is transmitted by infrared waves generated by the oscillatory motion of molecules. Infrared radiation is absorbed by molecules on the Earth. However, the Earth is heated by visible radiation coming from the Sun where oscillatory motion of molecules is extreme. This visible radiation passes through the atmosphere to reach the surface of the Earth. This incoming visible radiation from the Sun is then converted to infrared radiation which is then reflected back toward space.

The Greenhouse effect - the Earth emits long-wave, infrared radiation. A portion of the outgoing long-wave radiation encounters gases in the atmosphere which have chemical properties that prevent this energy from escaping. We say that the atmosphere is very good at adsorbing infrared radiation which heat is then stored in the atmosphere. The energy retained in the lower atmosphere causes the temperature at the Earth's surface to rise.

Greenhouse gases - water vapor accounts for about 80% of the natural greenhouse effect. Other greenhouse gases include carbon dioxide, nitrous oxide, ozone, and methane. Starting in 1958 measurements were made of carbon dioxide concentration in the atmosphere near the top of Mauna Loa volcano in Hawaii. Since that time the CO2 in the atmosphere has risen from 315 to 355 parts per million by volume. The rise is not linear but exponential. Because no known natural mechanism can explain such a rapid increase in CO2, the inescapable conclusion is that anthropogenic (human-generated) burning of fossil fuels must be a primary reason for the observed increase in CO2.

The Cretaceous Period is known for its huge carnivorous dinosaurs. Its climate was also one of the warmest in the Earth's history. Evidence for this warmth comes from a number of pieces of evidence in the fossil record. Warm-water marine faunas were wide-spread, coral reefs grew 5 to 15° closer to the poles than they do now. The sea level was 100 to 200 meters higher, implying the absence of polar ice sheets. Isotopic measurements of the deep-sea deposits indicate that intermediate and deep waters in the oceans were 15 to 20 °F warmer than now.

Why was the Cretaceous Climate so Warm? - Modeling simulations show that the middle Cretaceous arrangement of continents and oceans which influenced ocean circulation and planetary albedo, could account for nearly 5°C of warming. However, the model suggests that some other factor was involved and that factor was CO2, the greenhouse trace gas.

From where did the CO2 come? - Geological evidence points to an unusually high rate of volcanic activity in the Middle Cretaceous. Rates of continental drift were then about three times as great as now, implying increased extrusion rates at spreading ridges. Vast outpourings of lava created a succession of great undersea plateaus across the southern Pacific Ocean between 135 and 115 million years ago. The time of maximum Cretaceous warmth. Such a massive outpouring of lava likely released massive amounts of CO2. Some estimates are that CO2 reached 8 to 12 times preindustrial values.

Evidence for Global Warming - Instrumental measurements of temperature were rare before 1850 but in the period from 1850 measurements indicate that the globe has heated up about 0.5°C. Human activities have led to increasing atmospheric concentrations of carbon dioxide and other trace gases that have enhanced the greenhouse effect. During the next century global average temperature will likely increase at about 0.3°C per decade assuming emission rates do not change.

The environmental effects of global warming are listed as follows:

Global Precipitation changes -

Increased Storminess -

Melting of Glaciers -

Thawing of Frozen Ground

Evidence for Global Cooling - The 'Little Ice Age" and Climate Oscillations -- The "Little Ice Age" lasted from about A.D. 1450-1850. Worldwide temperatures were not actually vastly colder than at present; in eastern Europe, for example, average temperatures were just 1° to 1.5° C lower. However, the practical impact of this seemingly small drop in temperature was profound:

- High Mountains of Ethiopia were blanketed with snow

- The river Thames froze more than two dozen times and it has not completely frozen since the winter of 1813-1814.

- Reduced evaporation from the colder oceans led to devastating droughts in many parts of the world.

Ozone - In a layer between 25 and 35 km above the Earth's surface, ultraviolet radiation breaks down molecules of oxygen (O2) into two oxygen atoms that are then able to combine with other O2 molecules to form ozone (O3). The ozone layer protects us against the effects of ultraviolet light which will damage the immune system, produce cataracts, substantially increase the frequency of skin cancer, and cause genetic mutations. In 1985, British scientists reported a startling discovery: a vast hole, about the size of Canada, had developed in the Ozone layer above the Antarctic region. What happened?

Volcanoes and Climate - A volcanic eruption can release large amounts of sulfur dioxide into the atmosphere. The effect of SO2 is to reduce the amount of sunlight passing through the atmosphere. If the eruptions are large enough the amount of additional SO2 in the atmosphere can cause a net cooling of the climate. Aerosols from volcanoes also appear to have enhanced ozone depletion.