Almost 70% of the earth's surface is covered by water bodies which are referred to collectively as the hydrosphere. Although there is not extensive human activity in the hydrosphere itself, the intensive activities on the land threaten the biological richness of oceans and especially the coastal areas where about 60% of the world's population live. Although legislative measures are taken, their application cannot be achieved due to lack of reliable data, planning, management, international coordination, and technology transfer, and inadequate funds. The hydrosphere is polluted by sewage, agricultural chemicals, litter, plastics, radioactive substances, fertilizers, oil spills, and hydrocarbons. Land-borne pollution gets into the major hydrosphere through rivers and atmosphere. The hydrosphere is vulnerable to climate and atmospheric change including ozone depletion.
Water vapor accounts for about 94% of the natural greenhouse effect. The impact of atmospheric water vapor on the climate is complex and not well understood. It can both warm and cool the atmosphere. When water evaporates, it cools the surface from which it evaporates. In addition, heavy clouds block sunlight and reflect it back into space. On the other hand, thin cirrus clouds may tend to let solar energy in while keeping radiated energy from escaping into space. Also, moist air retains more heat than does dry air, so a humid atmosphere should be warmer than a dry one. On balance, it is believed that water vapor has a net warming effect.
The main concern about increased concentrations of atmospheric water vapor is the possibility of a strong positive feedback effect. As the climate warms more water evaporates thus increasing the amount of water vapor in the air. The increased concentration will, in turn, further warm the climate leading to a still higher level of water vapor in the atmosphere. This iterative cycle could go out of control, leading to damaging or even catastrophic temperature increases. However, there may be natural mechanisms to keep the climate in balance. The water vapor originates as a result of evapo-transpiration and moves between various spheres as shown in Fig. 2.6.
The transition of water from one environment to another and its transfer among them does occur naturally in the universe continuously with time. In nature, water movement depends on these transitions as well as transfers. The driving forces of such movements are the sun's radiation (solar energy) and earth's gravity. The col-
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Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.