CARBON DIOXIDE AND GLOBAL WARMING

HEAT ABSORPTION IN THE ATMOSPHERE If the temperatures of Venus and the Earth were determined only by their distances from the sun, their average temperatures would be 100oC and -18oC, respectively. In the atmospheres of both these planets, there exist molecules which absorb heat. Since much of the solar energy is retained around the planet instead of radiating into space, the planets are warmer than they otherwise would be. Venus, whose atmosphere is 96% CO2, has an average temp of 450oC. The earth's atmosphere possesses water vapor and CO2 which absorb heat and its average temp is 15oC.

These gases allow light to penetrate through the atmosphere but, in absorbing heat, they raise earth’s temperature. Because of this, these gases have been compared to the panes of a greenhouse roof and thus are often called “greenhouse gases”. About eighty-four percent of the sun’s energy is absorbed by molecules of the atmosphere rather than radiating directly into space—this is the “Greenhouse Effect”. Why do some molecules absorb heat? Each molecule has a specific shape as the atoms’ electrons try to maximize the distance between each other. These atoms can vibrate in their positions if packets of electromagnetic energy can be absorbed and each chemical bond is prepared to absorb energy of only certain wavelengths. (The forms of electromagnetic energy, which include heat, radio waves, light, UV light, and X-rays, differ in the length of their waves.) If infrared energy (heat) passes through molecules of carbon dioxide, certain wavelengths of this infrared energy are absorbed rather than transmitted (see the chart below). It is observed that carbon dioxide (CO2) can absorb infrared wavelengths of 4 and 15 microns. In other words, carbon dioxide absorbs heat.

Some of the sun’s energy is absorbed in the atmosphere rather than being

lost into space

ABSORPTION OF INFRARED WAVELENGTHS BY CARBON DIOXIDE

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Other molecules that absorb infrared such as methane (CH4), N2O, and chlorofluorocarbons (CFCs) are also greenhouse gases. Molecules such as oxygen (O2) and nitrogen (N2) don't absorb heat and are not greenhouse gases. What would happen if the amount of carbon dioxide in the atmosphere were to change? The concentration of carbon dioxide (CO2) in the atmosphere has not always been constant throughout earth's history, nor has the average temperature of the planet. The levels of CO2 in the early atmosphere were about 1000x what they were today. This higher concentration of CO2 was important for maintaining a temperature for the beginning of life since the sun, as a young star, produced less energy (25-30% less). These levels gradually receded as carbon dioxide dissolved in oceans and formed calcium carbonate which can then be incorporated into corals, sea shells, and eventually limestone. The ocean holds 20 times the amount of carbon as contained in all life on land, the terrestrial biomass. (There are an estimated 38,100 gigatons of carbon contained in the deep ocean and 1,020 in the surface ocean.)

Early in life’s history, the activity of living things began to change the amount of carbon in the atmosphere. Cyanobacteria and later algae performed photosynthesis and incorporated atmospheric carbon into organic matter. Living things are made of molecules of carbon and their activity can affect the amount of carbon dioxide in the air.CHEMICAL REACTIONS AND PHOTOSYNTHESIS In chemical reactions, chemical bonds between atoms are broken and atoms are rearranged to form different chemical substances. Atoms are never lost in chemical reactions—there are the same number of atoms in both the reactants and the products.

6 CO2 + 6 H2O + energy -----> C6H12O6 + 6O2

In the above reaction, going from left to right, carbon dioxide and water can be converted to glucose (a sugar) and oxygen gas. There are just as many carbon, oxygen, and hydrogen atoms in the reactants on the left as there are in the products on the right. The above reaction depicts the process of photosynthesis: plants take carbon dioxide from the air and water from their roots to create biomolecules such as sugar. In the process, oxygen is released as a waste. In the 17th century, a researcher named Van Helmont put a 5 pound tree in 200 lb. of soil. After 5 years, the tree weighed 170 lb. and the soil had lost only a few ounces. "It's the water!" he exclaimed, being half right. This observation refuted the idea of Aristotle that all of a plant’s matter came from the soil which had lasted almost 2000 years. Glucose molecules (which, when joined to gather to make long chains, make up cellulose and starch) make up most of a plant's weight. Glucose is made of C, H, and O atoms (carbon, hydrogen, and oxygen); these atoms can be gotten from the rearranging of water and carbon dioxide molecules. Carbon fixation is the incorporation of inorganic C (from carbon dioxide) into organic molecules.

Of course, the sugars and other biomolecules of plants are important to animals as well. Whether it is a butterfly drinking nectar, a deer eating leaves, or a human eating French fries, animals can use these biomolecules as an energy source and as a source of the biomolecules needed for growth. For example, when people eat French fries (plant starch makes up about half of the American diet), our cells break down the glucose molecules in a set of reactions which accomplishes the inverse of what occurred in photosynthesis.

C6H12O6 + 6O2----------------->6 CO2 + 6 H2O + energy Glucose and oxygen react to form carbon dioxide and water in a process known as cellular respiration. The carbon dioxide which you are exhaling right now came from the food you ate, which ultimately was produced by photosynthesis in plants. The energy released in the process is what we use to move, keep ourselves warm, and think. What happens to the biomolecules of a plant if an animal doesn’t eat them? Typically, decomposers—organisms such as bacteria and fungi—perform cellular respiration to break this dead matter into carbon dioxide and water (as in the mushrooms decomposing the dead tree stump).

Carbon is continually recycled through what is known as the carbon cycle. Plants convert carbon dioxide into organic matter. When animals eat plants and perform respiration to obtain energy or when decomposers break down dead plants or animals, the carbon in organic matter is converted to carbon dioxide once again. Does all of this organic matter get recycled? No. Think of a swamp for a minute. Every year, new organic matter ends up at the bottom of the swamp. Not all of it returns to carbon dioxide of the air—every year the “muck” just gets thicker and thicker. For hundreds of millions of years, living things have been buried before their organic molecules could be decomposed. The remains of countless living things of the past were compressed over long periods of time to produce petroleum and coal. Coal and the derivatives of petroleum (gasoline, kerosene, propane, methane) are carbon-based molecules, just as were the organic molecules from which they were produced. In the following drawings, black dots represent carbon atoms and red dots represent hydrogen atoms.

Over hundreds of millions of years, carbon atoms were taken from the air and were buried deep underground. Humans are changing that. Our energy needs drive us to dig and drill for this ancient coal, oil, and natural gas. When we burn these fossil fuels for energy (as in the combustion of two octane molecules in gasoline depicted below), the fossil fuels react with oxygen to form water and carbon dioxide. The combustion of fuel puts additional carbon dioxide into the air. The tar in the

Kerosene Methane Propane

following picture is a petroleum derivative; this carbon originated in ancient living things and had been buried for millions of years.

Carbon Reservoirs

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A gigaton of carbon is equal to about 2200 billion pounds. There is more carbon stored in fossil fuels than in the atmosphere, forests, soils, and surface ocean combined. (The deep ocean contains almost 8 times more carbon than stored in fossil fuels.) If all of fossil fuels were used, the global temperature would rise between 4.5 and 15oC which is warmer than the planet has been in the past 200 million years. One

gallon of gas (which includes molecules of octane whose combustion is depicted below) weighs 7 pounds and produces 22 pounds of carbon dioxide (Bowen, 2005).

Human activity is currently releasing an excess of 6-7 billion metric tons of C/year to the atmosphere which results in about a 3 billion ton/year gain in the atmosphere. Seventy percent of the global emissions of carbon dioxide results from fossil fuel use (WHO 1990a) although some results from deforestation (1-2 billion tons). Coal and oil currently contribute equal amounts of carbon into the atmosphere. Since world coal reserves are so much greater than world oil reserves, the percentage of carbon dioxide produced by coal emissions will probably increase. The average car releases 5 tons of carbon dioxide into the atmosphere per year. The burning of forests returns carbon into the air and the cropland and grassland which typically replace the lost forests only absorb 20% the CO2 that is absorb by the forest.

What are the effects of putting additional carbon dioxide molecules into the air?1) CARBON DIOXIDE LEVELS ARE RISING Globally, humanity is releasing more carbon dioxide than in the past. Since the beginning of the Industrial Revolution, CO2 levels have risen 25%. From 1860 to the present, CO2 concentration in the air has risen from 290 ppm (parts per million) to 350 ppm and is currently increasing at 1.5 ppm/yr. The amount of carbon dioxide released through human activity increased from 32 million tons/yr in the 1800s to 3.4 billion tons a year in the early 1900s. From the period of 1945 to the oil crisis in 1973 (at which point emissions were at 18.6 billion tons/yr), carbon dioxide emissions increased 5% a year (Bowen, 2005). Obviously, as the global population increases, so will its production of carbon dioxide. For each 1% increase in global population, carbon dioxide output increases 1.4%. This population driven increase in carbon dioxide output is greatest in developing countries (Shi, 2003). Since 1980, the carbon emissions of China have increased 80%. Humanity is currently burning four times the amount of fossil fuel used in 1950. The past and current generation are estimated to have contributed two thirds of the carbon dioxide responsible for modern climate change (Friedlingstein, 2005). America produces a disproportionate amount of carbon dioxide emissions. The average American releases 5 tons of carbon into the air per year. The average car releases 5 tons of carbon into the air per year. The United States produced 32% of the world’s carbon dioxide during the period of 1950 to 2000 with an estimated total of 182 billion tons (Blatt, 2005). The

2 MOLECULES OF OCTANE AND 25 MOLECULES OF O2 PRODUCE 16 MOLECULES OF CO2 AND 18 MOLECULES OF H20

amount of greenhouse gas emissions in the U.S. (with its 260 million people) is equivalent to those of 2.6 billion people living in more than 150 countries (Speth, 2004). The amount of carbon dioxide release from fossil fuel use in America increased more than 17% from 1990 to 2000 (U.S. Greenhouse Gas Inventory Program, 2002). There is a plant which generates electricity in Ohio which burns 7.5 million tons of coal a year and produces almost as much carbon dioxide as the entire world produced in the year 1800 (Bowen, 2005). Although the Unites States only composes 5% of the world’s population, we use 25% of the world’s energy.

2) THE GLOBAL TEMPERATURE IS RISING The planet has gotten warmer in recent decades. Average global temperature increased 0.6 degrees Celsius in the 1900s. One third of this change occurred in the period from 1990 to 2000 (IPCC, 2001). The 24 warmest years since 1900 have all occurred since 1973. The ten warmest years have all occurred since 1990 with 1998 being the hottest year on record (Blatt, 2005; Nordell, 2003; Liu, 2005; Patz, 2002). Prior to 1990, the 1980s was the warmest decade on record. The temperature of wells in Northern Canada has increased about 2 degrees Celsius (Majorowicz, 2004). The average temperature in Antarctica has increased 5oF since 1945 (Blatt, 2005). Global temperature is predicted to increase throughout the 21st century. Global warming models predict that the climate will warm at a rate of .15 degrees or more per decade over the next several decades (Hansen, 2001; WHO, 1990a) It is currently estimated that the average global temperature will increase by 1.4 to 5.8 degrees Celsius by the end of the 21st century (IPCC, 2001; Huntington, 2003). By the end of the 21st century, the global temperature will be higher and increasing more quickly than at any time in the past 140,000 years (Last, 1993).

3) AS POLAR ICE MELTS, SEA LEVELS RISE There are enormous amounts of water which are trapped in the polar ice caps and in the glaciers of the world. Throughout the majority of the history of the earth, the global temperature was higher than it is today, there were no polar ice caps, and sea level was higher than it is today. For example, in the mid-Cretaceous Period, much of the East Coast was underwater and an inland sea covered much of the interior of the North America. If all the earth’s ice were to melt, sea level would increase 150 feet and 15% of the U.S. would be underwater including the entire states of Massachusetts, Connecticut, Rhode Island, New Jersey, Delaware, Florida, and Louisiana and the cities of New York, Philadelphia, Miami, Seattle, and San Francisco (Blatt, 2005). Currently, polar ice is melting and sea levels are rising. World ocean temperatures are rising and sea level is currently rising at a rate of 1 inch/decade. Increases in temperature and the salinity variations have been reported from deep water off Antarctica (Smedsrud, 2005). Both the amount of Arctic and Antarctic ice is decreasing. Sometimes large pieces of ice break free such as a 48 mile x 22 mile piece of Antarctic ice in 1995. In Antarctica, the ice sheets of Western Antarctica are much more vulnerable to change than those in the eastern half, given nature of the terrain below the ice. In the past 25 years, the amount of annual ice over the Arctic ocean has decreased by 3% per decade (Laidre, 2005). Within 50 years, the amount of Arctic ice during summers may be sufficiently reduced to allow shipping through the Arctic (Speth, 2004; Blatt, 2005). Glacial ice is melting. A large amount of water is trapped in glaciers on mountains and in permafrost areas close to the poles. Much of this ice is melting as well. In 1992, it was reported that all mid- and low-latitude glaciers were retreating and the ice record within these glaciers indicated that this is the warmest 50 years of any in the past 12,000 years (Laidre, 2005). The amount of ground which is permanently frozen (permafrost) has decreased globally by 30% since 1900 (Blatt, 2005). The thickness of ice in Greenland is decreasing by about 3 feet a year. All the glaciers of Glacier National Park in the United States are expected to disappear in this century (Blatt, 2005). About 85% of the snowfields in the Western U.S. have decreased their volume since the 1950s. The famous snows of Mt. Kilimanjaro in Africa may be gone by the years 2010-2020. This mountain has already lost glaciers which were once thousands of feet thick. Mt Everest is 4 feet shorter than it once was and its glacier has retreated three miles. The

Eastern Himalayas have lost 20% of their glaciers in the past century and all the glaciers may be gone by the year 2035. In some areas, the glaciers retreat 500 feet per year (Bowen, 2005). By the end of the 21st century, the rise in sea level is expected to impact the lives of millions of people. In the 21st century, the global temperature is predicted to increase between 1.4 and 5.8 degrees Celsius which would increase sea level somewhere between 9 and 88 centimeters (IPCC, 2001). An increase of 25 cm would have serious consequences on the delta regions of the Nile, Ganges, and Yangtze Rivers and would require the evacuation of many small island nations of the Indian Ocean and the Pacific. A one meter rise in sea level increase would flood many coastal areas, such as the beaches of the eastern United States. Florida, Louisiana, and North Carolina would be most affected; the Louisiana coast could lie 30 miles inland of its present location. A number of cities such as Venice, Bangkok, and Taipei would be threatened. Eighty percent of the Marshall Islands would be underwater. A one meter increase would flood up to 15% of the arable land in Egypt, 11% of the land of Bangladesh (where the floods of 1987-8 displaced millions of people), and require the raising of most of Miami’s bridges and reconstruction costs to 1/3 of Miami’s area. More than 100 million people would be displaced. Some coastal areas depend on underground freshwater aquifers (such Miami) which would be threatened by saltwater intrusion (IPCC, 1990; Mizra, 2002).

4) WEATHER CHANGES AND EXTREME WEATHER Changing weather patterns could increase the numbers of droughts, floods, and fires. At first, a little bit of global warming might not seem alarming. After all, many people would actually prefer to have a slightly warmer climate than what they currently experience. However, changes in global temperature would affect a number of aspects of the climate. Rainfall patterns could shift and this would affect the crops which could be grown in agricultural regions. This change will increase the ratio of rain to snow and significantly decrease the amount of runoff in the Northeast U.S (Huntington, 2003). California depends on melted snowfall for much of its water and warmer weather could increase the frequency of drought (as observed in the warm years 1990-1 when the snow pack had lost 15% volume and California experienced severe drought). In order to feed the ever growing world population, world rice production must increase at a rate of about 1% per year. Unfortunately, global warming (and, more specifically, increases in the minimum temperatures during the dry season) decrease the productivity of rice crops. It is estimated that for each increase in dry season minimum temperature of 1 degree Celsius, grain yield can decline by as much as 10% (Pen, 2004). In warmer seasons, destructive fires more common in the West and the Florida everglades. Areas of the southeastern United States have recently undergone the worst drought on record. In coastal areas, decreased rainfall has led to an increased salinity of coastal estuaries and other wetlands (Thomson, 2002). Global warming will change rainfall patterns and increase the number of severe storms. The frequency of severe storms has been increasing and many areas of the U.S., such as the eastern states, has received an increased amount of rainfall (Blatt, 2005). An increase in the number and severity of floods are expected. Many areas of the Northeast United States have experienced record flooding in recent years. In the U.S., flooding causes $6 billion in damages annually. The floods throughout the Midwest in the summer of 1993 cost $16 billion in damages. During this time the Mississippi rose 46 feet over its normal level and three feet over its record level (Blatt, 2005). About 60% of the country of Bangladesh is less than 20 feet above sea level and is vulnerable to seasonal floods. On average, about 21% of Bangladesh is flooded per year with as much as 70% in severe floods. As a result of global warming, Africa will experience higher levels of desertification and additional droughts and floods. Asia will experience an increase in the number of tropical cyclones which will displace tens of millions of people (IPCC, 2001).

Warmer temperatures lead to increases in the number and severity of hurricanes. When the surface temperature of ocean water increases 1oF, the risk of hurricanes doubles. Forty five million Americans live in coastal areas vulnerable to hurricanes (Blatt, 2005). Recent years have seen an increase in the number of hurricanes and tropical storms. In 2003, three simultaneous hurricanes existed in different regions of the Caribbean and Atlantic; this was the first time such an event was observed. In 2004, a record number of hurricanes (four) hit Florida. In 2005, the hurricane season began earlier than ever before, ended later than ever before, and witnessed the

greatest number of hurricanes and tropical storms (including several which reached Category 5 strength). In 2005, hurricane Katrina (which was a Category 5 storm just before landfall) flooded New Orleans, costing more than 1,300 lives and $125 billion in damage.

5) OTHER EFFECTS OF GLOBAL WARMING Global warming will affect human health through an increase in the incidence of disease. Global warming is likely to increase the incidence of infectious disease by increasing the abundance and geographic distribution of organisms which cause or carry disease, reducing availability of water in some regions, and causing economic and political problems which will reduce resources allocated to health care. Increases in extreme weather and changes in rainfall patterns are likely to disrupt agriculture, leading to malnutrition and disease susceptibility in many areas (Khasnis, 2005). Insect species (such as mosquito species which can carry diseases ranging from malaria to yellow fever) could spread to new latitudes and altitudes. Greater flooding caused by global warming will increase the spread of certain diseases such as cholera (Patz, 2002). Higher temperatures increase the growth of weeds, molds, and fungi which are contributing to the increase in asthma rates in children (Ault, 2004).

Climate change will affect plants and animals. Warming temperatures affect the distribution of animals. For example, robins have extended their range to 250 miles north of the Arctic Circle (Blatt, 2005). Global warming seems to be responsible for earlier flowering dates of plants (including crops like wheat) in the U.S. (Hu, 2006). The decrease of Antarctic ice, combined with changing water temperatures, currents, and salinity are affecting marine life (Laidre, 2005). Global warming threatens to allow non-indigenous species to spread into new areas where they can increase at the expense of native plants and animals. The increase in maximum and minimum temperatures in an area seem to have a greater effect than increases in the annual average temperature (Stachowicz, 2002). The habitat change which would result from global warming would threaten many species with extinction (Hilbert, 2004). Even common species could experience significant decrease in range (Meynecke, 2004). Even the remotest parts of the arctic seem to be displaying effects caused by global warming such as earlier summers, the reduction of glaciers, a change in biological species, and thinning of sea ice (Smol, 2005).

When the temperature of water increases, less gas can be dissolved in it. Increased global temperatures will decrease the amount of oxygen which can be dissolved in the world’s oceans (Keeling, 2002).

COMPLICATING FACTORS At first glance, it might seem that the greenhouse effect is a fairly simple phenomenon: Carbon dioxide absorbs heat, fossil fuel burning produces more carbon dioxide and, as a result, global temperatures rise and the poles melt. Of course, we all know that predicting the weather from day to day is difficult enough, predicting global trends and identifying the causal factors is much more challenging. There are a number of complicating factors.1) Not all scientists agree. Do all scientists agree on an accepted model of the greenhouse effects, the severity of its effects, and the cost of moderating these effects? Of course not. The data on this incredibly complex system is still being processed and new hypotheses are constantly being tested. This is true of any healthy science. While it is true that not all scientists agree, it should also be emphasized that the basic aspects of our understanding of the greenhouse effect are agreed upon by the vast majority of climate experts, such as the more than 2,500 climate experts of more than 60 nations which compose the International Panel on Climate Change, IPCC. Waiting for 100% consensus before implementing plans to control emissions would make the situation more difficult. For example, emission reductions of 60% would be required in the year 2020 to accomplish what 17% emission reductions could accomplish if implemented in the year 2000.2) The Changing Amounts of CO2 Absorbed

Estimating the effects of CO2 is complex since every change in atmospheric levels can change the amounts that forests, phytoplankton, and the ocean can absorb (remember that most of the earth’s carbon is already stored in the deep ocean). Increased carbon dioxide may enhance plant productivity although any such increases would likely be more than balanced by the difficulties plants would face due to changes in climate and rainfall. One study indicated that increase in tree growth due to increasing carbon dioxide levels was minor. 3) Aerosols and Particulates are Cooling the Planet Even if the climate is changing, can we be sure that human activity (anthropogenic forces) are the cause? It is certain that human activity is responsible for some of the observed climate changes. There are natural phenomena such as the solar sunspot cycle and methane release from wetlands which could increase global temperature and other natural phenomena such as volcanic eruptions which would have a cooling effect. Aerosols (which are liquid droplets so small that they can be suspended in the air such as sulfate aerosols produced from fossil fuel combustion) have a cooling affect on the atmosphere by blocking solar radiation and through their effects on clouds (such as increasing cloud brightness, cloud cover, and longevity). Including aerosol data with that of carbon dioxide better explains the changes that using data from carbon dioxide alone. Particulates are small pieces of solid materials dispersed into the atmosphere. Many particulates block sunlight and thus have a cooling effect. Large volcanic eruptions can cause measurable drops in global temperature.

4) Other Greenhouse Gases Some have argued that while CO2 does cause global warming, most of the recent increase in global temperature has been due to other gases such as chlorofluorocarbons (CFCs) and N2O. CFCs are discussed in the next unit; N2O levels are increasing slowly but steadily through the use of fertilizers and the burning of biomass. Methane is a greenhouse gas which, in addition to that which is produced naturally, is released into the atmosphere by rice agriculture, domestic cattle, landfill and sewage decomposition, and leakage from natural gas pipelines. Seventy-three million metric tons of methane are produced through cattle belching and flatulence alone. It may be easier and cheaper to reduce the amount of these other greenhouse gases than to reduce carbon dioxide emissions.