Science, Climate Change, and the Greenhouse Effect
In the 1800’s, scientist began to understand the role greenhouse gases had in keeping the Earth warm. The greenhouse effect is now a well established scientific principle. Both the science and the data show that current global warming is caused by the increasing CO2 in the atmosphere.
Greenhouse Effect: Most gardeners know how greenhouses work. In the daytime, the sun’s radiation (visible and UV) comes in through the glass and warms the plants and soil. The glass stops the heat radiation in the infrared (IR) region from passing back through and the greenhouse stays warm enough to keep the plants from freezing, even at night. The Earth works much the same way except greenhouse gases, primarily water and carbon dioxide, play the role of the glass and trap some of the leaving IR radiation. Winter nights on Earth would be very cold without greenhouse gases.
Earth’s Energy Balance: Of the Sun’s energy coming to Earth, 30% is reflected immediately back into space by particles in the air, by clouds, and by the surface. Another 20% is absorbed by the atmosphere where it runs the weather cycle. The remaining 50% heats the land and oceans. All the absorbed heat is eventually radiated back into space as infrared radiation. It’s a balanced energy budget, 100% in and 100% back out. Anything that reflects more light back into space, such as an increase in particulate matter in the air, would cause the Earth to cool. Anything that delays the energy’s trip back to space, such as an increase in greenhouse gases, would cause the Earth to warm. There are many small things that affect the Earth’s energy balance, but the main three are the Sun, particulates, and greenhouse gases.The ash from the explosive eruption of Mt.Tambora in 1816 caused that year to be called the year without a summer, worldwide.
The Sun: Certainly a change in the Solar radiation the Earth receives would cause a change in the Earth’s temperature. Small wobbles in the Earth’s orbit, the Milankovitch Cycles, are variations in the eccentricity, axial tilt, and precession of the Earth’s orbit. They affect the amount of solar radiation the Earth receives in predictable cycles. Both scientists and skeptics agree that these cycles are responsible for the Ice Ages that occur in roughly 100,000-year intervals. In the part of the cycle where the Earth receives more solar radiation, the oceans slowly warm and release CO2. The CO2 further amplifies the warming by the greenhouse effect. As the Earth moves into the part of the cycle where it receives less solar radiation, the oceans slowly cool, the CO2 dissolves back into the oceans and another ice age starts. The patterns of wobble in the Earth’s orbit are predictable and the model predicts that a minor cooling trend, which began some 6,000 years ago, will continue for the next 23,000 years. The current warming trend is too rapid and in the wrong direction to be a part of the Milankovitch Cycles.
The Sun also has cycles where its output varies slightly such as Sunspots activity. They cause the amount of solar radiation to vary in approximately 11-year cycles. However, the effects of Sunspots are so small that they do not show up above the other small variations in NASA’s temperature record.(see below). Long term variations in the Sun’s intensity are not responsible for the current warming. The graph of solar irradiance from 1880 to the present in this article shows that the Sun’s intensity increased slightly from 1880 to 1960 and then has declined slightly since 1960. Satellite measurements of solar radiation show also that the solar radiation reaching Earth has declined slightly over the last 30 years – yet the Earth still warmed.
Temperature Data: The best temperature data we have clearly shows the Earth is getting warmer. NASA has compiled the Earth’s average temperature for each year since 1880 by using ships logs, weather stations, and satellite measurements. In the graph below , each square dot shows how far that year’s average temperature was above or below the 1970 value. Although the data varies widely from year to year because of random factors such as sunspots, weather events, ocean current, and particulates from volcanoes and man’s activities, the trend is clearly upward. The solid red and blue lines are moving averages, which make the trend easier to follow.
Temperature Trend: The greenhouse effect links some of the causes of the temperature trend to man’s activities. The trend took a turn upward in about 1920. That was when the automobile, industrialization, and energy production began further increasing the carbon dioxide concentration in the air. The trend was flat from about 1945 to 1975 and that can be attributed mostly to particulates. There was an increase in particulates after 1945 from many sources such as WW II, atmospheric nuclear testing, and increased industrialization. Research during the early 1970’s showed a huge increase in aerosols from power production, increased industrialization, and vehicles and some alarmists even speculated that we might be causing another ice age. Particulates are visible and cause immediate health problems so by 1980 most industrialized countries had restrictions on particulate release. During the period from1945 to 1975 the CO2 concentration had continued to rise but its effect had been masked by the particulates. Reducing the particulates in the air allowed the full effect of the CO2 to be felt, causing the Earth’s temperature to begin to rise again. The effect of particulates and the reliability of the temperature record can clearly be seen in the graph above. In 1991, Mt. Pinaturbo erupted spewing about 10 cubic kilometers of ash into the air which caused an immediate 0.3 °C temperature drop for the entire Earth, lasting until about 1995.
Causality: Although the greenhouse effect is a well accepted principle, skeptics sometimes claim the correlation between global warming and CO2 does not constitute causality. However, G.N. Plass, in 1956, calculated the climate sensitivity of the Earth to CO2. He found that doubling the concentration of CO2 in the air would cause a 3 to 4 °C increase in the Earth’s temperature. A number of more recent studies have confirmed his work and have shown that, though the concentration of CO2 in the air is small, it accounts for about 25% of the greenhouse effect. No natural occurrences such as volcanoes, sunspots, fires, or dust storms can account for the major trend in the data. Certainly, the increasing amount of CO2 in the air is causing the Earth to warm.
Man’s Role: Man’s activities, mainly through deforestation and burning fossil fuels, have released large amounts of CO2 into the air. In the last century, man’s emission of CO2 from fossil fuels have increased to over 30 billion tons annually and the concentration of CO2 in the air has risen from 280 parts per million (ppm) to 385 ppm. The processes that remove carbon dioxide from the air takes decades or longer so as the carbon dioxide concentration slowly built up, the Earth became a better greenhouse. The concentration of carbon dioxide in the air is now 38% higher than in 1880 and the Earth’s temperature is about 0.8°C (or 1.3 °F) higher. Clearly, man’s activities are mainly responsible for increasing the CO2 concentration in the air – and the increasing CO2 concentration is causing global warming.
(C) 2010 J.C. Moore
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