A PRIMER ON GLOBAL WARMING

As the World Conference on Climate Change in Copenhagen (Thursday and Friday) approaches interest in this global problem has increased as well as the political and economic consequences of actually addressing it. Accordingly, this last weekend I found myself responding to a question from a friend: "Do you believe this stuff on global warming?"

I answered in the affirmative. "The science of it is compelling."

"Science? Aint this jest politics?"

I quickly added, "No! It is very simple. It all has to do with carbon dioxide!"

"Yeah, I knew thaaaaat," yelped my friend.

I continued quickly without a pause, I knew I had only a minute or two of this person's attention span before me. "In the beginning...volcanoes on the primitive earth belched forth huge amounts of carbon dioxide and water. Over millions of years --nearly 500 million--that early atmosphere, rich in carbon dioxide and water, was slowly altered when primitive plants and other living things evolved. Since plants remove CO2 from the atmosphere and convert it into organic solids and over long periods of time geological processes sequestered these carbon-bearing substances underground. Slowly, carbon dioxide became a very rare gas--less than 0.02% by volume of the total. With a lower concentration of this heat-trapping gas, the earth cooled. In the last million years or so, modern man evolved and has learned how to mine the carbon based buried substances, bring them to the surface,burn them in the atmosphere and add carbon dioxide back into the atmosphere--and reconstitute the ancient hot climate of millions of years ago." I said, setting down the beer mug exactly back into its circular water stain from which I had lifted it.

"Oh yeah?"

"Yeah!"

That was as far as we proceeded with that conversation. Later on I though about what I should have said, so I add it here.

So you want to know what the basic science of global warming is, huh?

One must start with the idea that the earth interacts with sun's radiation just like any solid body. It absorbs solar radiation then as a warm body it re-radiates that energy back into space as heat. Eventually, it reaches some average temperature which is a balance between the radiation absorbed and the heat radiated away. As long as those conditions remain unchanged, planet earth, will reach some stable average temperature and remain there. (Though of course surface temperatures over the body may fluctuate wildly from a high-when its surface is exposed to the sun--during the day--to a low--when it surface is shielded from the sun--at night)

The earth follows basic principles of physics, its acts as a "black body" absorbing and re-radiating the sun's energy. However, one critical difference is that the earth has an atmosphere, a thick transparent film of gases which clings to its surface and subtly, but significantly alters the way the absorbed heat leaves the surface.

Think of yourself sitting in front of a large window on a sunny, cold, winter day. The sun streams through the glass and warms your face and body, yet if you place your hand on the glass of the window--the pane remains cold to the touch. The sun's radiation passes through the glass without heating it. But it is absorbed by your body--it heats you. You can readily feel the heat. That is a good analogy of what happens to the sun's rays as they pass through the atmosphere. They are nearly unchanged by the mostly transparent atmosphere, and are absorbed at the earth's surface. The earth's atmosphere is heated from the bottom up.

When solar rays strike the earth's surface they are absorbed and heat that surface. Of course, some surfaces absorb more radiation than others and get warmer than others. Snow or ice fields for example absorbs very little solar radiation, while darker surfaces such as deserts absorb more sunlight and heat up to higher temperatures. Once heated however, the earth's surface re-radiates its heat. However, this "earth radiation" or heat radiation is different than the light and other rays of solar radiation. As the radiant heat passes upward through the blanket of atmospheric gases the earth radiation interacts with certain molecules in the atmosphere to transfer the radiant energy to them. They heat up and transfer that heat to the atmosphere in general. Its temperature rises. Without this effect the earth would be very much colder than it is.

The atmosphere is composed of a mixture of gases--mostly nitrogen (78%) and oxygen (21%) with small amounts of carbon dioxide, methane, nitrous oxide and many other gases in trace amounts--and variable amounts of water vapor. Water vapor is very common in the atmosphere. Because of its molecular shape water molecules readily interact with earth radiation. It is a good absorber of earth radiation and readily heats up. Humid places on earth, such as tropical forests for example, are for this reason warmer than they would be based on the amount of radiation they receive, while deserts--where water vapor is scarce--even in equatorial regions-- can be loose the heat they absorbed during the day very quickly and get very cold at night, since there is little water vapor to trap heat.

Though water vapor is very effective in its absorption of earth radiation, it is a conservative gas...the atmosphere can hold only a certain amount. When its concentration increases, the air may reach saturation. No more water vapor enters the air and any additional water vapor forms swarms of tiny liquid droplets we know as clouds, or fog--or ice crystals--as well and other forms of condensation. Thus, the amount of heat-trapping water vapor in the air is naturally limited...it varies from place to place and time to time, but overall it remains a constant--since when it is too much it is naturally voided from the air as clouds, fogs or as ice crystals and ultimately may fall from the sky in the form of precipitation.

But other gases such as carbon dioxide, nitrous oxide, and methane are not conservative. They have molecular shapes which can interact with earth radiation and absorb earth radiation, and their concentration can change over time. Carbon dioxide is the most important. It is a most effective absorber of earth heat. Do to its presence (and other gases) the earth would be 60 degrees F cooler than it is at present. In the modern atmosphere CO2 presently accounts for less than 0.04% (by volume--see below). Yet it is an effective and important heat- trapping gas. One had only to look toward the planet Venus to understand how effective this gas is as a heat trapping agent (though other effects also play a part) Venus is near to the earth, and of nearly the same size, but unlike the earth, it has an atmosphere that is nearly 97% carbon dioxide--and a surface temperature that is about 900 degrees F.

Note that I discuss here only carbon dioxide, but two other gases-- methane and nitrous oxide-- are also heat trapping gases though not as effective as the former. Perhaps I will discuss their impact in a future blog.

On earth carbon dioxide in the atmosphere is an integral part of the great carbon cycle. As a gas it is absorbed by plants through their leaves to form sugars in the presence of chlorophyll and sunlight to form sugars by photosynthesis. In that process CO2 combines with water (H2O) to produce simple carbohydrates which plants use as building blocks to produce complex sugars, cellulose and starch. In the process, plants--which get the energy for this reaction from sun light and the photolysis (breaking apart) of water molecules--release oxygen as a waste product. Animals use oxygen to oxidize plant-derived sugars and generate energy for their life-processes, and in the process release CO2. There is a lovely balance here, a great cycle-- and in primordial nature..a balance existed between plants and animals. As a result of this balance, the level of CO2 remained remarkably static for hundreds of thousands of years--as did the earth's temperature.

As long as the actions of early human beings remained within the confines of this natural system, there were few changes in the carbon dioxide concentration or the temperature of the atmosphere. When humans mastered fire, the burned wood for fuel, but they added no additional carbon dioxide to the atmosphere..since the carbon of wood was removed by plants--and in the burning of the wood the carbon of the wood is oxidized and reenters the atmosphere as carbon dioxide--and this maintains a steady state for carbon. [As noted above, in the distant past, volcanic activity added large amounts of carbon dioxide to the air. Ancient atmospheres of hundreds of millions of years ago had much higher concentrations of this gas when volcanic activity was more common. However that ancient carbon was taken up by plants and sequestered underground by biochemical and geological processes. At present, volcanism generates less than 1% of the carbon dioxide humans produce.]

Early humans evolved with weak jaws and teeth and relatively small bodies, but they had a large brain--and two hands to manipulate their immediate environment. They soon learned how to make tools, chop down forests (which effectively remove carbon dioxide),dig up long-buried sources of carbon in the form of peat, coal, oil and gas and use these as fuels, raise farm animals which release methane gas, and burn limestone to produce lime-mortar and concrete which release CO2 as well. Recall that the "fossil fuels" humans turned to for fuel were formed millions of years ago by the storage of carbon compounds by ancient plants and animals, and had remained buried by geological processes.

By unearthing of these long-sequestered carbon sources and burning them in the atmosphere (i.e. combining the ancient carbon with the oxygen of the air as in your furnace, automobile, or gas fired fire-place) more recent humans have altered the existing carbon cycle. Human actions have caused an increase in the concentration of CO2 which had been steady at about 200-280 ppmv for millennia. Since the advent of mining fossil fuels and their use as fuel in the early 1800s the end-product of that process--carbon dioxide gas has been rising steadily in concentration.

Based on analysis of air bubbles in glacial ice, the pre-industrial carbon dioxide concentrations in
the atmosphere ranged between 200 and 280 parts per million by volume (ppmv). For example, an ice core measurement for the year 1832 indicated a carbon dioxide concentration of 284 ppmv, or about 100 ppmv lower than it is now. (See: Wikipedia.org)

The "new" carbon derived from fossil fuels is without question "anthropomorphic" i.e. generated by human activity. Burning petroleum,coal and natural gas are (in that order) the most important sources of anthropomorphic carbon dioxide additions to the atmosphere. In addition, more carbon dioxide is produced in the manufacture of cement ( which is an important contributor, but less than the others. Portland cement--so widely used in the modern world--is produced by burning limestone to drive off CO2 to produce what is known as "slaked lime" or CaO. When mixed with sand and water and exposed to the air the slaked lime reabsorbs CO2 from the atmosphere to form CaCO3 crystals (similar to those in the limestone that was its source). All that heating of limestone to by burning fossil fuels to form the slaked lime generates a great deal of waste CO2--thus its listing here.

There is an interesting natural variation in carbon dioxide concentration in that atmosphere which fluctuates from 3-9 ppmv seasonally and follows the growing season in the Northern Hemisphere. (Since that hemisphere has the most land area and biomass.) As plants grow they take up carbon dioxide and that lowers in the atmospheric carbon, and conversely as they stop growing and decay the concentration rises. The peak CO2 level occurs in May as the growing season just begins and the minimum is in October at the end of the growing season. See Wikipedia]

Recall from above that the present 2008 concentration of carbon dioxide is nearly 0.04%, or more precisely it is: 0.0385% by volume. Stated in parts per million by volume that is more frequently referred to as "385 ppmv" (parts per million by volume).

As noted earlier, this value has been consistently rising and in a predictable way. Beginning in 1965 direct measurements of this gas over Hawaii, in the near-center of the Pacific Ocean, recorded a value of 320 ppmv, by 1989 the value had increased to 350 ppmv, and by 1995 is was 360 ppmv, in 2000, 370 ppmv of carbon dioxide was recorded. Today in 2009 the value is somewhere above 385 ppmv.

Why does the level of the gas rise so predictably?

One has only to measure how much coal, oil or gas a nation burns to calculate the amount of carbon dioxide is being generated by those actions. (Wikipedia informs me that the US burns 1.1 trillion tons of coal each year (one ton of coal produces nearly two tons of CO2), and almost 8 billion barrels of oil per year where one barrel produces nearly one half ton (US) of CO2.) It is a simple chemical equation. Enormous amounts of coal, oil, gas, gasoline and other fossil fuels are burned each year. Measurements of the amount of carbon dioxide added annually to the atmosphere is easily calculated based on how much fossil fuel we consume. For example each gallon of gas burned generates about 8.8 kg of CO2, or about 19.4 pounds of CO2 gas which is released into the atmosphere. So one can simply multiply the number of gallons burned each year to calculate the gasoline-derived component. Then add to that the amount from coal, petroleum and other sources. Credible estimates of the total world production of carbon dioxide indicate an annual additon to the atmospher of about twenty-eight billion metric tons. Twenty-eight billion metric tons of CO2 each year has its effects on the graph of the CO2 concentration in the atmosphere. Each year there are more of us and we all use more and more fossil fuels.

Most knowledgeable observers and many scientists consider the 1989 level of 350 ppmv as a "safe" level for the world and a target level for world leaders to aim for as they consider abatement of addition of CO2 gas to the atmospher. Remember the case of Venus and its surface temperature of 900 degrees F.

It seems clear that the reason the year 2008 was the hottest on record (at least since records have been taken) has much to do with the fact that the level of carbon dioxide was more than one third higher than it was in the pre-industrial years of the early 19th Century.

What nations are mostly responsible for this burden of carbon dioxide?

Well those nations which are presently highly industrialized are mostly responsible. It is an interesting fact that nearly one third of the more than six billion people on the earth or about two billion people still heat their houses and cook their food with wood. They remain free from fossil fuels and barring the aerosol soot produced by their home fires they have little culpability in the global warming problem. However carbon dioxide releases are easily calculated for each nation.

The two nations which contribute more that 40% of the world total of released caron dioxide gas--one is of a modest-sized population (about 308 million), but has an enormous and profligate fossil energy habit, while the other has about average fossil use habits, but has a very large (1.3 billion) population. Those two nations are the USA and China.

China and the US each pump about 20% of the world's total waste CO2 into the world's air. The USA with only 4.5% of the world's population (in 2009 = 6.8 billion) dumps about 6 billion metric tons of carbon dioxide gas each year as does China with 1.3 billion people. The two nation's total,of about 12 billion metric tons, is about 40% of the world's total 28 billion metric tons. Other large scale carbon dumpers are: the EU (population = 499 million and 7% of world population), which contributes about 4 billion metric tons or about 14% of the total. Thus, the total carbon pollution of these three political entities: China, USA and the EU represents more than half (54%) of the world's total.

For a credible response to this world ecological crisis those three political entities must agree to certain restrictions on CO2 dumping.

In terms of per capita pollution, the figures are equally interesting and informative. The world average amount of carbon dioxide dumped per person is about 4 metric tons. Citizens of some nations exceed that amount by a wide margin, while others produce much less. Each US resident is responsible for nearly 19 metric tons of carbon dioxide per year, or nearly five times the world average. On the other hand, Chinese citizens dump only about five tons each, or one-fifth of the amount a US citizen contributes. EU individuals contribute about 8 tons each, less than half of the US citizen, while Russian and Japanese individuals contribute about 10 tons each (about one-half of a US citizen), and the Indian citizen releases the least--less than 2 tons each, or about one-tenth of a US citizen.

It is apparent that climate is one of the many factors in these measurements. India's low consumption level is in part related to its ecomomy, and its generally temperate climate. Citizens in colder climates require more heat energy to meet their energy needs and do so by increased fossil fuel consumption. Another example is Mexico which has an average level of carbon dioxide production per person of about 4 metric tons per year, while neighboring Canada releases19 metric tons of carbon dioxide per person.

Get the (preliminary) picture?

rjk