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Science, Global Warming, and the Ice Age Mystery

Fri ,31/12/2010

In the early 1800’s, scientists began a search for the cause of the ice ages. That search has led to a discovery of the factors that affect the Earth’s temperature, an understanding of the current global warming, and the solution to the mystery of the ice ages. *

The Data: Science is a way of understanding nature by using observation and reason. Man has always been keenly interested in the weather, but temperature records before 1850 were mostly historical accounts of storms, heat waves, or when bodies of water froze. Thermometers came into use in about 1850, allowing more accurate temperature records. One of the most useful records is NASA’s graph of the Earth’s annual mean temperature, which was compiled from ships logs, weather stations, and satellite measurements. It serves as a scorecard for telling whether the Earth is getting warmer or cooler. NASA’s data has small random variations from year to year because of factors such as sunspots, weather events, ocean currents, and particulates from volcanic eruptions. However, NASA’s graph shows that the Earth’s temperature has clearly trended upward since 1880 – with the exception of a curious plateau from 1945 to 1975 followed by a steeper rise in temperature. The Earth’s mean temperature is now 1.3 F higher than in 1880, and the last decade has been the hottest on record. Any theories or causes put forward to explain the global warming trend must be consistent with the temperature observations.

Possible Causes: Nineteenth century scientists realized from geological evidence that the Earth had gone through many ice ages that alternated with ages of warmer climate. Much of the early research on global warming was a search for the cause of the ice ages. Scientists found that many small variables cause the Earth to warm and cool, but the main three causes are the Sun, particulates, and greenhouse gases.

The Sun’s output seems to have been reasonably stable over the last several million years. Satellite measurements over the last 30 years have shown that while solar radiation has declined ever so slightly during that time, the Earth continued to warm – so clearly changes in the Sun’s output is not the cause of the recent warming. The amount of sunlight the Earth receives does, however, depend on the Milankovitch Cycles. These cycles are small variations in the eccentricity, axial tilt, and precession of the Earth’s orbit that cause the solar insolation, the amount of sunlight the Earth receives, to vary slightly in predictable cycles. Ice core data shows that ice ages tend to occur in roughly 100,000-year cycles that match the timing of the Milankovitch cycles. The temperature between the ice ages and the warm periods, however, are much greater than would be caused by the changes in solar radiation alone. Though a clue to the cause of the ice ages, the Milankovitch Cycles are not the cause of the current warming. They predict 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 for the Milankovitch Cycles to be the cause.

Particulates cause the Earth to cool by reflecting incoming sunlight back into space. The role of particulates in cooling the Earth became apparent in 1816 when ash from the explosive eruption of Mt.Tambora caused that year to be called “the year without a summer”, worldwide. The curious plateau in NASA’s temperature record from 1945 to 1975 was primarily caused by particulates from sources such as WW II, atmospheric nuclear testing, and increased industrialization. Research during the early 1970’s showed a huge increase in aerosol particulates from power production, factories, and vehicles – and some alarmists even speculated that we might cause another ice age. Particulates are visible and cause immediate health problems, so by 1980 most industrialized countries had restrictions on particulate emissions. Particulates cannot be the cause of global warming, but reducing their sources can cause the temperature to rise as can be seen in the temperature record after 1980.

The Greenhouse Effect was discovered in the early1800’s when scientists realized that the Earth was kept warm at night because the atmosphere trapped invisible heat rays rising from the surface. Around 1860, John Tyndall identified the invisible rays as infrared radiation and found the main gases that trapped the heat rays to be water vapor and CO2. The amount of water in the air remains relatively constant because of the water cycle. When the humidity is low, water evaporates, and when the humidity gets too high, it rains. However, CO2 has no such restrictions. Since CO2 makes up only a few hundredths of a percent of the air, it was at first dismissed as a possible cause of warming, especially since it was thought that plants and the oceans would absorb any excess.

In 1896, Svante Arrhenius, while still pursuing the idea that variations in CO2 might be the cause of the ice ages, laboriously calculated the effect of cutting the amount of CO2 in the atmosphere by half. He found that doing so would lower the temperature of Europe by 4-5 C, perhaps enough to bring on an ice age. He also found that doubling the amount of CO2 might raise the temperature of the atmosphere by 6-7 C. No one was concerned as Arrhenius’ model of the atmosphere was very crude and it was inconceivable that the amount of CO2 in the air could ever double. Some scientists speculated that man should intentionally add more CO2 to the air to ward off another ice age.

As models of the atmosphere improved, a number of scientists tried to get a better estimate of the effect of doubling the amount of CO2 on the Earth’s temperature, but the increasing complexity of the models made the calculations daunting. A breakthrough came with the development of computers. In 1956, G.N. Plass calculated that doubling the concentration of CO2 in the air would cause a 3 to 4 C increase in the Earth’s temperature. ** Many dismissed his work, as it seemed impossible that CO2, which made up only 0.03% of the air, could have such a large effect on temperature. However, in 1997, J.T. Kiehl found that, under clear sky conditions, CO2 accounted for 26% of the greenhouse effect – with water vapor accounting for most of the rest. More recent research has confirmed their work . Clearly, CO2 could have a significant effect on the Earth’s temperature if it was increasing. But was it?

CO2: In 1900, Arvid Hgbom calculated the amount of CO2 emitted by industrial sources and, surprisingly, found that man was adding CO2 to the atmosphere at roughly the same rate as volcanoes. No one thought much of it as, at that rate, it would take centuries for the amount of CO2 to increase significantly. However, after a protracted heat wave during the 1930’s, Guy Callendar re-examined previous temperature and CO2 measurements and found not only that the Earth was getting warmer, but also that atmospheric CO2 concentrations were increasing rapidly. Callendar’s work was mostly ignored, but a few scientists began monitoring the concentration of CO2 more closely. Their results were sporadic but, by 1958, Charles Keeling had established accurate procedures for measuring atmospheric CO2. His lab was eventually moved to the Mauna Loa observatory, far away from most CO2 sources. His graph showing how CO2 varies with time, now called the Keeling curve, proved to be an important piece of evidence. It showed that the oceans and plants were not taking up CO2 nearly as fast as man was producing it. Over the last century, the atmospheric CO2 concentration has risen from 280 parts per million (ppm) to 385 ppm, a 38% increase, and the Earth’s temperature has risen by 0.8 0C, well in line with Plass’ prediction. The role of CO2 as the major cause of global warming had been convincingly established. There is yet one more piece of evidence that confirms that conclusion.

Ice Ages: It was now possible to solve the mystery of the ice ages. The Milankovitch cycles alone cannot explain the changes in the Earth’s temperature during the cycles, but the process becomes clear if CO2 is included. The ice core data shows that the concentration of CO2 falls to about 180 ppm during an ice age and rises to about 280 ppm during the warm part of the cycle. The changing CO2 concentration happens because the solubility of CO2 in water varies with temperature. In the part of the cycle where the Earth is warmed by the increasing solar radiation, the oceans release CO2, which further amplifies the warming by the greenhouse effect. In the part of the cycle where the solar energy decreases, the oceans cool, the CO2 dissolves again, and another ice age begins. The concentration of CO2 in the atmosphere is the “control knob” for the Earth’s temperature – and we have now turned the knob up to 380 ppm and are moving it even higher. The Earth will surely get warmer.

* Much of the historical data came from this excellent AIP article.

 **  Recent research in the Journal of Climate, covering the last five ice ages, has experimentally confirmed Plass’ estimate of the climate sensitivity.

(C) 2010 J.C. Moore

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Science, Climate Change, and the Greenhouse Effect

Mon ,13/12/2010

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.

This image has an empty alt attribute; its file name is NASA-GISS-2010A-1.jpg

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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Is It Climate Change or Global Warming?

Tue ,02/11/2010

The term climate change and global warming are often used interchangeably as they refer to the same environmental problem. Some people prefer to use climate change as climate is more evident to us and climate change is not as controversial as global warming. It is probably okay to use either term, but for those who like precision in language, we will take a tour through climate science to sort out the difference.

Climate and Weather: It is said that no one can predict the weather and that is true as no one can predict very far in advance whether it will rain or storm or how cold or hot it will be. However, if we observe the weather of a region over a long period of time, a pattern emerges. That pattern is the climate and, though we cannot predict the weather accurately, we have a much better chance of predicting climate. If we observe such things as the high and low temperatures, the amount of rain, when the first frost and the last freeze usually occurs, a pattern emerges. The climate is quite important to us as it determines the crops we grow, the types of house we build, and the clothing we wear. Climate determines the plants, animals, and insects that live in our region and even the types of health problems and diseases. The factors that determine climate have been observed to vary slowly with time and we expect the climate in a region to remain relatively stable over long periods.

Climate Change: In the last century, and particularly in the last three decades, we have noticed that climates in many regions of the Earth are changing. The daytime high temperatures are higher, the nighttime lows are warmer, the patterns of drought and rainfall have changed, and storms seemed to have become stronger. Frost occurs later in the year and the last freeze occurs earlier, which has caused gardening zones to move. The ranges of many species of plants, animals, insects and bacteria have shifted, and there has been invasions of non-native, sometimes invasive, species into new areas. Our observations have shown that the climate is definitely changing, and those changes are sure to have consequences for us.

Global Warming: Since the early 1800’s, scientists have been concerned with whether our use of fossil fuels has affected the temperature of the Earth. With an increasing understanding of the role greenhouse gases play in stabilizing the temperature of the Earth, scientist wondered whether burning fossil fuels might affect the energy balance of the Earth. Burning carbon fuels releases carbon dioxide, CO2, which they knew to be an important greenhouse gas and there was speculation about whether an increase of CO2 in the air could actually cause the Earth to warm. Critics of the idea argued that water was a much more important, that the relatively small amount of CO2 in the air would not make a difference, and that the amount of CO2 man produced was minuscule compared to what was already there.

The Role of CO2: With a better understanding of the atmosphere and the advent of computers, G. N. Plass in 1956 was able to calculate 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. Certainly, increasing the amount of CO2 in the air should cause the Earth to warm. In the last century, our emission of CO2 has increased from a minuscule amount to over 50 billion tons annually and the concentration of CO2 in the air has risen from 280 parts per million (ppm) to 385 ppm. But, has that caused global warming?

The Temperature Scorecard: The temperatures over the Earth vary widely from place to place with the weather and the season. However, the temperature of a particular place measured over a long period of time has a pattern and we can use the pattern as a scorecard. There are temperature records that go back to about 1850 and these have given us a way to keep track of whether the Earth is warming. By using ships logs, weather stations, and satellite measurements, NASA has compiled the Earth’s annual mean temperature from 1880 to the present. Though it varies widely from year to year, the Earth’s annual mean temperature shows an upward trend and the Earth is definitely getting warmer.The scorecard shows that over the last century the Earth has warmed about 1.3°F, which does not sound like much. However, since that is the average over the whole Earth, it represents a tremendous amount of energy and it is the energy in the atmosphere that drives our weather and determines our climate.

So there we have it, a cause and effect relationship. Climate change is caused by global warming, which in turn is caused by the increasing CO2 in the atmosphere, and the CO2 is increasing because of our use of fossil fuels. Though it is probably irrelevant whether we call it climate change or global warming, it is very relevant that we understand the relationships and think about our role. The way we use fossil fuels has consequences for us and for the rest of the species on the planet.

(c) 2010 J.C. Moore

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