AIR: SOME IDEAS P.Rhines, 21 Feb 2003 This is by no means a complete summary (see the lecture hand-outs, and available on the web site, and your own notes and lab books)…but it reviews some of the important ideas. In the Air unit we described Great, Large and Small aspects of the atmosphere. Just as the problem of terrorism is that it does not respect or relate to national borders, air pollution is ‘without borders, being global as well as local. We spoke of James Lovelock’s Gaia theory, which describes the Earth as a living organism, one in which the living plants and animals control the chemistry of the atmosphere and ocean, and in doing so stabilize them. We said that Darwin’s evolution of species answers the question, ‘Why are we here?’ and ‘why are all the living species here?’; Lovelock’s Gaia tries to answer the question ‘Why is the Earth the way it is?’, with an oxygen rich atmosphere when its neighbors Venus and Mars are lifeless, burnt out planets with carbon dioxide atmospheres. Indeed, ‘Why are rocks and oceans and ocean sediments the way they are?’ Lovelock spoke of a redwood tree in analogy, the tree being mostly dead, but supporting the living layer just beneath the bark. A coral reef is mostly dead, yet its surface is alive, and it grows. Richard Feynmann’s description of a tree is a beautiful counterpoint to this (‘….a tree is made of air, mostly…’). We have seen the greenhouse effect at many scales: solar box cookers trap sunlight (short-wave, easily penetrating glass or clear plastic), converting it to ‘heat radiation (long-wave, infra-red) which does not penetrate through glass or plastic. In just the same way the atmosphere traps solar heating and warms us; our average temperature is about 33 C (59F) greater it would be with no atmosphere (the moon which has no atmosphere but receives similar sunlight is about that much colder). CO2 contributes only 1/2800 th of air, which is mostly nitrogen, then oxygen. The trapped radiation bounces back and forth between upper atmosphere and ground, at a rate 47% greater than the sunlight arriving above (Lovins p236). The increasing greenhouse gas effect on climate (due to carbon dioxide, methane, ozone and other trace gases) appears to produce a definitely ‘global’ warming but it is not simple and uniform everywhere. Carbon dioxide has increased from about 280 parts per million (a concentration of 2.8 x 10-4) before industrialization to 370 parts per million in 2000. Monitoring atmospheric CO2 is pretty easy, because it is pretty uniform around the Earth. So the station on top of the volcano Mauna Loa on the big island of Hawaii established by Charles Keeling shows what we need to know: nearly steady increase, along with seasonal up-and- down due to the ‘breathing’ of the green plants which is greatest in northern spring season. Earth’s plant life uses solar energy to take in carbon dioxide and put out oxygen…photosynthesis…while animals do the reverse. The microcosm experimentshows both sides of this cycle: millefoil plants and goldfish, with strong cycling of oxygen and nutrient ‘foods’. Note that the solar energy is accessed only by the plants, and the animals become chemical-heat engines when they eat the plants. The atmosphere has its general-circulation patterns like the westerly (that is, to the east) winds at middle latitudes and easterly (toward the west) at low latitudes (the tropics, roughly equatorward of latitude 22). The easterlies are called ‘trade winds’ because sailing ships could use them to go westward, rather than sail upwind at higher latitude. In addition to the mean east-west winds the air veers north and south in a regular pattern of waves (see Lec air-2), due to the major mountain ranges and land-sea contrast (warm/cold contrast). Finally on top of this we have ‘weather’, the 1000 km wide cyclonic and anticyclonic wind systems associated with low and high pressure centers, respectively. There are ‘storm tracks’ where the westerly winds come out over the ocean, and intensify. In the Atlantic the storms often then to do follow the mean winds northeastward toward Iceland. In the Pacific they come more eastward out across the Pacific. The storm tracks show up on maps of time-averaged pressure as bigger low-pressure regions (called the Icelandic Low [North Atlantic] and Aleutian Low [North Pacific]). In the southern hemisphere things are different because there is so little land. There we have a parade of weather moving more rapidly round the world in the westerlies. Weather involves intense storms (low-pressure centers), in the extreme case hurricanes, tropical cyclones and tornadoes. Hurricanes are ‘heat engines’ driven by very the warm tropical ocean surface. When they come over land they quickly die out. Generally they are born near the Equator and as they intensify, the Coriolis force carries them away from the tropics toward middle latitudes. Intense storms do damage: roughly $35 billion for Hurricane Andrew which hit south Florida in 1992. It is widely thought that it would have cost $100 billion if it had hit Miami. In under-developed countries there is not so much real estate to be lost but instead lives are lost: more than 12,000 died in Hurricane Mitch which sat over the highlands of Central America in 1998. One of the great sadnesses of tragedies in the 3d World is that the number of victims, and the identities of many, will never be known. It dumped several feet of rainwater on the steep slopes, which had in places been denuded of vegetation. Villages were swept away. The prime minister of Honduras said that the countries infrastructure was nearly totally destroyed. So the lesson is that poor countries suffer casualties and rich countries lose real estate. But the case of Bangladesh, where tropical cyclones are particularly fierce, is important. The loss of jobs, farms, fresh water, infrastructure may be as devastating as the loss of lives (which exceeded 300,000 in one day in Nov. 1970). Yet to put even this tragedy in perspective, in the civil war with Pakistan at about the same time, more than a millionlives were lost as India and ‘east Pakistan’ created the independent country of Bangladesh. . At the smaller scale we briefly described the major pollutants in the lower atmosphere, which are reviewed both in McNeill’s and Lomborg’s books.