Water And Vapor

Quite clearly, the results of farming depend on adequate and timely sup-plies of water. The critical factor is not rainfall but soil moisture throughout the life history of the crop involved. As everyone with house plants or a garden knows, the appropriate conditions depend on the plant species, the stage of growth, the properties of the soil, and air temperature and humidity. Water in the soil feeds and cools growing vegetation as it passes into the plant through the root systems. The flow of fluid transports nutrients into the stems and leaves. When the air is hot and dry, the tomatoes of the leaves open and a great deal of water vapor transpires into the air. In the process, the plant is cooled. In a sense, this is the vegetative equivalent to human perspiration. Because of uncertainties about the quantity and scheduling of watering needed to achieve optimum crop yields, irrigation practices have been less than maximally efficient. Vegetation can survive and even thrive in moderately dry soil, but when there is inadequate water, leaves begin to wilt. A heavy rainfall or deep irrigation will improve the health of the plants, but will not entirely undo the harm caused by the desiccation. This means, of course, that when irrigation is available, a grower should not wait for signs of distress; that is, the plant should not be used as a measure of water insufficiency. The crucial factor, soil moisture, should be monitored directly. A procedure widely recommended to the home gardener is poking a metal rod or digging a few inches into the soil to see if it is wet. Water should be applied when the soil is dry. Surprisingly, in arid regions, where irrigation is a necessary practice, ,a great many plants are killed by over-watering. This happens when an amateur farmer, seeing dry surfaces, incorrectly assumes that the dryness extends into the root zone. 

Commercial farmers sometimes use soil augers to gags the state of the soil. Another approach is to install electronic moisture sensors whose out-puts are recorded continuously. Some authorities believe these procedures are inadequate because they do not measure the wetness at enough points through a deep layer of earth. An alternative approach to the monitoring of soil moisture is to maintain a water budget of the cultivated field. This involves measuring the water added by precipitation and irrigation and balancing it against the water leaving the field by evaporation and transpiration. This requires computation of the last two processes, which are often lumped together and called transpiration. 

the growth of a thunderstorm

the growth of a thunderstorm is impeded by a stable layer sometimes a temperature inversion—that serves as a lid over the cloud top. Asia thunderstorm matures, a draftsman develops adjacent to the updraft core. Both drafts arc composed of churning high-speed air resembling a tumbling stream of rushing water. This pattern of air motion accounts for the turbulence: experienced by an airplane flying through a thunderstorm. The drafts may carry an airplane up or down while eddies in air velocity buffet it and, in extreme cases, muse structural damage. Most thunderstorms pass through their lifetimes in less than an hour, yielding a few lightning strokes and rain. Provided no one is struck by lightning, these storms do a great deal more good than harm. The rain is usually very beneficial, particularly to farms. The cool air that precedes an arriving thunderstorm on a hot summer day is the result of air from high altitudes being cooled by the evaporation of water drops; the air descends to the ground and spreads out, mostly in the direction of the storm motion. Some thunderstorms, because of their large sizes and long duration, arc called "supermodel" thunderstorms. They can last for many hours and have strung, persistent updrafts and downdrafts. They commonly occur as parts of a squall line, a line of thunderstorms, often oriented northeast-southwest, that sweeps across the Great Plains ahead of an advancing cold front. Super cell storms an produce violent weather. They are the sources of tornadoes and hail. As these storms move over the flatland of Kansas, Nebraska, Iowa, Illinois, and surrounding states, they sometimes lay down swaths of hail that devastate wheat, corn, and soybeans (Figure 3-16). In an average year, hail damage to agriculture in the United States amounts to more than 5700 million. Hailstorms also cause widespread damage in many other parts of the world: the fruit orchards of northern Italy, the grapevines of the Caucasus region of the Soviet Union, the tea plantations in Kenya, the farmlands of South Africa and Argentina. In India, 246 people were killed during a severe hailstorm near New Delhi in April 1888.

                                           

The Atmosphere and the Weather

storms accompanying low pressure centers associated with fronts are some-times called "frontal cyclones." References to cyclones are often misunderstood; they usually evoke thoughts of violent weather. There is some justification for such a reaction: Over the central United States, tornadoes are commonly called cyclones; in Southeast Asia, Australia, and Mexico, the name is applied to the intense tropical storms known as hurricanes in the United States. These are not improper uses of the name, although most cyclones over the earth are centers of low pressure that do not contain threatening weather. The middle latitudes of the earth experience, at regular intervals, the passage of cyclones with their associated clouds and precipitation. On weather satellite photographs, cyclones sometimes have very distinctive patterns (Figure 3-7). Some places see more of them than others do because there are favored regions for the formation of cyclones. Cyclones most often develop along well-established, nearly stationary fronts. In winter, cold air from the Arctic commonly sweeps southward.

                                         

over North America behind a cold front, pushing warm air ahead of it. Usually the Rocky Mountains act as a barrier that stops the air from moving westward. As a result, the front separating the polar air over the Great Plains from warmer air becomes stationary along the eastern foothills of the Rocky Mountains. Many cyclones develop along this front, particularly over Colorado (Figure 3-8). On a weather map, a new cyclone first appears on the front as a wavelike wiggle that coincides with an area of falling atmospheric pressure. In some cases, the wave amplitude increases and pressure continues to decrease. Clouds appear, which thicken, become widespread, and even-tually yield rain or snow. As all this is going on, the cyclone usually moves more or less eastward under the influence of the major west wind currents dominating the middle latitudes. In winter, polar air often pushes southward until the front becomes stationary in the form of a giant arc along the Gulf coast and up the eastern seaboard. Cyclones frequently develop along this front and move north-ward or northeastward. Many of them originate over the Gulf. Another favorite spawning ground is just off Cape Hatteras, North Carolina. 

Carbon Trading

Enthusiasm is spreading for cap and trade systems to regulate the amount of carbon dioxide (CO₂) emitted to Earth's atmosphere. In 1990, the U.S. Environmental Protection Agency set a limit on sulfur dioxide (SO₂) emissions from obvious point sources and allowed those who emit less than their quota to trade excess allowances. As a result, regional acid deposition was dramatically reduced. Can the world do the same for CO₂ ? Fundamental differences in the bio geochemistry of SO₂ and CO₂ suggest that establishing a comprehensive, market-based cap and trade system for CO₂ will be difficult. For SO₂, anthropocentric point sources (largely coal-fired power plants), which are relatively easy to control, dominate emissions to the atmosphere.

Natural' sources, such as volcanic emanations, are comparatively small, so reductions of the anthropocentric component can potentially have a great impact, and chemical reactions ensure a short lifetime of CO₂ in the atmosphere.CO₂ , in contrast, comes from many distributed sources, some sensitive to climate, others sensitive to human disturbance such as cutting forests. It is thus impossible to control all of the potential sources. combustion are one of the smaller components of the atmospheric flux of CO₂. which is dome• noted by exchange between forests and the oceans. During most of the past so,000 years, the uptake and loss of CO₂ from forests and the oceans must have been closely balanced, because atmospheric CO₂  showed' little variation until the start of the Industrial Revolution. CO, from coal, oil, and natural gas combustion now comics from many segments of society. including electric power generation, industry, home heating, and transportation. Unbalanced by equivalent anthropological sinks for carbon, fossil fuel emissions account for the vast majority of the rise of CO₂ in Earth's atmosphere. Caps on emissions, like those instituted for SO₂ ,will be difficult to institute if the burden of reducing CO₂  is to be borne equally by all emitters. Because land plants take up CO₂  in photo syn• thesis and store the carbon in biomass, forests and soils seem to be attractive venues to store CO₂ . Market•based schemes propose substantial payments and credits to those who achieve net carbon storage in forestry and agriculture, but these projected gains are often small and dispersed over large areas. Carbon Trading news in freshsciencenews
 We will need to net any such carbon uptake against what might have occurred without climate-policy intervention. Conversely, will Canada and Russia be billed for incremental CO₂  releases that stem from the warming of cold northern soils as a result of global warming from the use of fossil fuels worldwide? If credit is given to those who choose not to cut existing forests, the increasing total demand for forest products will shift deforestation to other areas.

Carbon Trading Over Taxes

As the United States moves inevitably toward climate legislation, discussion has shifted from the science to the policy options for slowing emissions of carbon dioxide CO₂ and other greenhouse gases. Some favor a tax on CO₂ emissions—referred to as a C tax (r). Others favor government subsidies (2). If high enough to alter consumer behavior, a carbon tax would reduce emissions by raising the effective price of carbon-intensive energy relative to carbon-free sources. Subsidies may speed development of specific, targeted low-C technologies. But a market-based system with an economy wide cap on emissions and trading of emission allowances would do the same, while having distinct advantages 0). Most important, a cap and trade system, coupled with adequate enforcement, would assure that environmental goals actually would be achieved by a certain date. Given the potential for escalating damages and the urgent need to meet specific emission targets (4), such certainty is a major advantage. A federal cap and trade system could be incorporated into existing emissions-trading frame-works and markets, such as the Kyoto Protocol's international market or sub rational ones like the Regional Greenhouse Gas Initiative. Earth's climate is agnostic about the location and type of CO₂ emissions and is sensitive only to the total burden of CO₂ It makes sense, therefore, to design a climate policy that taps all possible avenues to limit net  CO₂ emissions. Trading of emissions Science news articles across all sectors of the economy addresses this by allowing emitters to purchase carbon offsets from businesses that are able to lower their own emissions below their allocation. If trading were incorporated into an international system, U.S. firms and consumers could meet emissions targets at reduced costs by substituting less expensive cuts in, for example, developing countries, for expensive emissions cuts in the United States. Because investment would be funneled to technologies that reduce CO₂ emissions at the least ant, the overall expense of the program would be minimized. Cutting emissions of pollutants is admittedly notes  complicate crosscutting      CO₂        emissions, and transaction costs can be a factor. Nevertheless, the United States was able to reduce sulfur oxide emissions ahead of schedule and at 30% of the projected cost using a market-based cap and trade system (5). Elimination of lead from gasp. line and phaseout of ozone-depleting chemicals were also facilitated by emissions-trading programs.