Introduction

Water Freedom System

Survive Global Water Shortages

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The growing population of today's world (6.7 billion, U.S. Census Bureau, 2008) faces great challenges due to limited resources for the production of adequate amounts of food, fiber, feed, industrial products, and ecosystem services. As the global population increases by nearly 80 million each year, policies must be developed to ensure the needs of a future population of 8 billion by 2025 and more than 12 billion by 2050 (U.N. Population Division, 2008) are met. About 84% of this growth is expected to occur in developing countries. Since there is essentially no new arable land that can be cultivated, the increased food supply must primarily come from more intensive cultivation of existing arable land. Furthermore, with intensive agriculture, soil degradation will become a major concern. The world's water resource is also finite, and the increased demands will result in reduced availability of water for agriculture. Urban communities do not generally give high priority to the preservation of agricultural resources, such as land and water. In many highly populated countries, food and fiber needs are being met by irrigating up to 75% of the arable land and introducing high yielding cultivars of most grain crops that have higher input use efficiency thus maximizing production. In addition, the benefits humans derive from natural ecosystems, such as marketable products and goods (i.e., timber, fish, pharmaceuticals), recreational opportunities (i.e., camping, boating, hunting, hiking, fishing), maintaining biodiversity, aesthetic and spiritual experiences, and other services (i.e., erosion control, water purification, carbon sequestration, oxygen production), are being threatened by the growing human population through habitat destruction and air and water pollution. In addition to these stresses, there is a threat of global climate change due to increased greenhouse gas concentrations in the atmosphere and the depletion of the ozone layer assumedly due to anthropogenic activities.

Climate change is not a new phenomenon. The planet's climate has changed tremendously over geological time, and the changes are still occurring. However, what appears to be different is the possibility of a new driving force and the cause of the climate change. Changes that were observed over a geological time period now occur over a shorter time span, particularly since the beginning of the industrial revolution. Apparently, human activities are causing climate change. Concentrations of key anthropogenic greenhouse gases, such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and tropospheric ozone (O3) have reached their highest levels ever, primarily due to the combustion of fossil fuels, agriculture, and land-use changes. Pre-industrial concentrations of CO2, CH4, and N2O were about 280 ppm, 700 ppb, and 270 ppb, respectively. Ozone depleting chemicals, such as chlorofluorocarbons (CFC-11) and hydrofluorocarbons (HFC-23), did not exist during that period, and perfluoromethane was about 40 ppt. The current CO2 concentration is about 380 ppm (increasing at the rate of 1.9 ppm/year), CH4 is about 1745 ppb (7.0 ppb/year), and N2O is about 314 ppb (0.8 ppb/year) (IPCC, 2007). Even if we curtail emissions today, these gases will stay in the atmosphere for a long time as the atmospheric lifetimes for these chemicals vary (5 to 200 years for CO2, 12 years for methane, and 114 years for N2O). These changes in the atmospheric chemistry are causing the so called "greenhouse" effect (Fig. 14.1(a)).

Figure 14.1 Process of global warming (a) and stratospheric ozone depletion (b). Long wave radiation is absorbed by various greenhouse gases in the atmosphere leading to increased temperatures. Anthropogenic emissions of chlorofluorocarbons (CFCs), hydrofluorocarbons, and bromocarbons released in the troposphere move up into the stratosphere. Upon exposure to radiation, atomic chlorine or bromine is released; these react with ozone and convert into oxygen, leading to depletion of ozone. Stratospheric ozone depletion leads to an increase in UV radiation reaching the earth's surface. Adapted with permission from Prasad et al. (2003b)

Figure 14.1 Process of global warming (a) and stratospheric ozone depletion (b). Long wave radiation is absorbed by various greenhouse gases in the atmosphere leading to increased temperatures. Anthropogenic emissions of chlorofluorocarbons (CFCs), hydrofluorocarbons, and bromocarbons released in the troposphere move up into the stratosphere. Upon exposure to radiation, atomic chlorine or bromine is released; these react with ozone and convert into oxygen, leading to depletion of ozone. Stratospheric ozone depletion leads to an increase in UV radiation reaching the earth's surface. Adapted with permission from Prasad et al. (2003b)

As the sun's energy passes through the atmosphere and warms the earth's surface, some is reflected back into the atmosphere and dissipates into space. The greenhouse effect refers to accumulation of specific gases that absorb the reflected radiation, effectively trapping heat in the lower atmosphere similar to what occurs in a glasshouse. The most important heat trapping gases are CO2, water vapor, CH4, N2O, CFC-11, and ozone.

If current greenhouse gas emission rates continue, both agricultural and natural ecosystems will face enormous pressure from the stresses caused by these heat trapping gases. Past changes have presumably resulted in an increase in global temperature of about 0.6°C over the last century. Climate models project even greater warming during the 21st century. The CO2 concentration is projected to reach 405 ppm to 460 ppm by 2025, 445 ppm to 640 ppm by 2050, and 720 ppm to 1,020 ppm by 2100 (IPCC, 2007). The projected global mean temperature increases (above values in 1990) for those CO2 stabilization scenarios are 0.4°C - 1.1 °C by 2025, 0.8°C-2.6°C by 2050, and 1.4°C-5.8°C by 2100. Similarly, the projected mean sea level rise for these same periods is 3 cm -14 cm, 5 cm - 32 cm, and 9 cm - 88 cm, respectively. These changes in climate were unprecedented during the last 10,000 years. It is also projected that all land areas will warm more rapidly than the global average, particularly at high northern latitudes in the cold season. Projections additionally indicate there will be more hot days, fewer cold days, cold waves, and frost days, and a reduced diurnal temperature range with higher nighttime temperatures. As the world becomes warmer, the hydrological cycle will also become more intense, resulting in more uneven and intense precipitation. This will result in increased summer drying and an associated risk of both droughts and floods. The projected climate change will have both beneficial and adverse effects on environmental as well as socioeconomic systems, but the larger and more abrupt climate changes will cause more adverse effects to be more damaging, particularly on seed-bearing plants.

In addition to the greenhouse effect, another phenomenon known as "ozone hole" is occurring. Ozone, a form of oxygen, plays two roles in the atmosphere. Near the ground, ozone is an air pollutant and a minor greenhouse gas that damages human health and the environment. In the upper atmosphere, known as the stratosphere (10 miles to 30 miles above the earth's surface), ozone forms a layer that helps protect life on earth from the ultraviolet (UV) radiation; sun's harmful rays. The term "ozone hole" refers to the thinning of this layer due to chemical reactions in the stratosphere, especially at higher latitudes, that are caused by the release of ozone-depleting chemicals known as halocarbons (Fig. 14.1(b)). The rate of change in chlorofluorocarbons (CFC) has declined due to the agreement of member countries to the guidelines proposed by the Montreal Protocol. Nonetheless, the concentrations are still high (268 ppb), and other chemicals, such as HFC-23 and perfluoromethane, are present at about 14 ppt and 80 ppt, respectively. Atmospheric concentrations of many of these gases are either decreasing or increasing in response to reduced emissions under the regulations of the Montreal Protocol and its amendments. However, the resident atmospheric times for these chemicals vary greatly (45 years for CFC-11, 260 years for HFC-23, and more than 50,000 years for perfluoromethane), and will have long-term effects on climate systems. Thus, the ozone layer within the stratosphere has thinned substantially, resulting in an increased ground-level UV radiation of about 35% from the pre-industrial period.

There are strong chemical interactions between greenhouse gases and ozone. Ozone and CFCs are minor greenhouse gases. Several gases involved in the ozone depletion chemistry are also greenhouse gases. For example, water vapor,

CH4, and N2O can ultimately lead to increases of stratospheric gases (such as NO2), which can catalytically destroy ozone. It is predicted that increases in greenhouse gases could delay recovery of ozone and may even lead to increased ozone depletion late in the current century (Randeniya et al., 2002; McKenzie et al., 2003). Another chemical feedback is concerned with decreased stratospheric temperatures that could occur as a result of future global warming at the earth's surface. This will tend to slow reactions that destroy ozone at mid-latitudes and thus, may facilitate recovery of the ozone layer (Rosenfield et al., 2002). Ozone depletion at high latitudes proceeds much more rapidly through heterogeneous chemistry on the surfaces of ice and acid crystals that occur when temperatures are below a critical threshold which could be influenced by global warming and delay ozone recovery in the polar region. Several radiative feedback processes also exist (McKenzie et al., 2003). Increases in temperature can lead to changes in cloud cover, rainfall patterns, ice accumulation, and surface albedo. Similarly, radiative changes caused by stratospheric ozone depletion have offset some global warming effects, and could, in the event of future ozone recovery, exacerbate future global warming. Interactions between ozone depletion and global warming are complex. It is suggested that although current ozone depletion is dominated by chlorine and bromine (Fig. 14.1(b)) in the stratosphere, in the longer term (~100 years), the impact of climate change will dominate through the effects of changes in atmospheric dynamics and chemistry (McKenzie et al., 2003).

The main consequence of ozone depletion is increased UV radiation reaching the earth's surface. Ultraviolet radiation is an electromagnetic form of energy that comes from the sun. This energy is classified into several regions based on wavelength, which is measured in nanometers (nm). One nanometer is a millionth of a millimeter. The shorter the wavelength is, the greater the energy of the radiation. The main components of radiation in order of decreasing energy are gamma rays, X-rays, UV, visible light, infrared radiation, microwaves, and radio waves. Ultraviolet radiation is further divided into three categories based on wavelength: UV-A (between 320 nm and 400 nm); UV-B (between 280 nm and 320 nm); and UV-C (between 200 nm and 280 nm). Calculations based on relations with total ozone and total irradiance suggests that UV irradiance has increased since the early 1980s by 6% -14% in middle and high latitudes of the northern and southern hemispheres. It is projected that every 1% decrease in ozone will increase UV exposure by 2% - 3% in the lower atmosphere.

Shorter wavelength radiation causes more damage to biological systems. UV-A is the least damaging component within the UV spectrum and reaches the earth's surface in large quantities. Both UV-B and UV-C are very harmful. Most UV-C radiation is absorbed by ozone, rarely reaching the stratosphere and never reaching the earth's surface. UV-B radiation is most likely to reach the earth's surface with increased ozone depletion. Factors, such as altitude, latitude, and time of day, influence the amount of UV-B exposure. Current global terrestrial UV-B radiation levels range between 0 and 12 kJ m on a given day with near

Equator and mid-latitudes receiving higher doses (Total Ozone Mapping Spectrometer, 2009, http://toms. gsfc. nasa. gov/ery_uv/euv_v8. html). Small increases in solar UV-B radiation can have substantial effects on plants at both the cellular and the whole-plant levels. Relationship and plant responses to various climate change factors are illustrated in Fig. 14.2.

Figure 14.2 Linkages between various facets of greenhouse gas emissions, climate change, ecosystem goods and services, and drivers of adaptations and mitigation

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