ࡱ> GIF3 *jbjb^^ Zh<h<$l $JJJJJJJJhjjjjjj, |JJJJJJJJJ.JJh,,Jhhh> ٜnx^hhh11h Importance of this Unit to the Course 1-6 This unit provides basic information on oxides of nitrogen and sulfur and ozone in the lower atmosphere that will be needed for understanding why some but not all chemicals contribute to global warming, ozone depletion, and acid rain covered in future units. 1-7 Some of the changes in atmospheric chemistry since the beginning of the Industrial Revolution, as discussed in previous units, lead to formation of acidic compounds. Deposition of some of these materials at the Earths surface will reduce crop yields and will affect the presence and distribution of species in terrestrial and aquatic ecosystems, particularly sensitive members of such ecosystems as will be discussed in Block 3. 1-8 Certain chemicals manufactured for commercial use do not occur in nature. When these chemicals are released into the environment they may have unintended consequences under conditions or at locations not considered in product safety tests. This unit provides information on such chemicals so that we have scientific basis for discussing possible need for regulatory action and public policy as will be discussed in Block 3. 1-9 Atmospheric conditions in the upper atmosphere as described in previous units create conditions of temperature and radiation beyond the range of those present near the Earths surface. These conditions transform certain environmentally benign chemicals into materials detrimental to humans and ecosystems as will be discussed in later units. 1-10 The ocean exchanges heat, water, and trace gases with the atmosphere and, being a fluid, moves heat and biological materials horizontally around the globe and vertically near continents. This information in needed for understanding the climate system, global warming, and ocean biology that are described in other units. 1-11 Water can exist as a solid, liquid, or vapor and has quite different physical and chemical properties in each phase. Information in this unit will be needed to understand the global energy balance changes in sea level due to global warming as well as biological and agricultural systems. 1-12 The characteristics of solar radiation and atmospheric chemistry as described in previous units will be used in this unit as a basis for understanding the heating and cooling of the Earths surface. What we learn in this unit will be the basis for understanding global warming and its consequences for the future of ecosystems. 1-13 Clouds are a part of the hydrological cycle as described in a previous unit, and they reflect and absorb energy as described the unit on the energy balance. These factors mean that clouds will play a critical role in climate and our ability to make models of climate as will be discussed in Block 2. 2-1 Because the earths climate can be described, in an abstract sense, by mathematical equations, we can get some indication of the properties of future climates by examining the properties of these equations. We find that these equations are the same ones that describe chaotic behavior in physical systems, which provides motivation to look at past records (unit on paleoclimate) for evidence of chaos in past climates. 2-2 In previous units we have seen that changes in the chemistry of our atmosphere are causing changes in the global energy balance. To understand how these changes will translate into changes in climate on a global and regional basis we need to use climate models. The results of these models will used in Blocks 2 and 3 to show how future environmental conditions such as water supplies, agriculture, natural ecosystems will differ from the present. 2-3 As discussed in previous units, the amount of carbon dioxide will double the pre-industrial revolution level before the end of this century and may reach 3 or 4 times that level. These different scenarios will create different climates that need to be described by the use of models so that we have the best available information on what adaptation strategies will be needed and what national and global policies might be necessary to protect sensitive components of the climate system. 2-4 The equilibrium climate models described in the previous unit are somewhat simplified to give quick results of possible future climates. They overlook a key factor that the ocean, atmosphere and ice change at different rates when external heating of the climate system changes. Better evaluations of climate models and better projections of future climates can be done with transient models. Transient models give better estimates about when we can expect significant climate changes to occur. 2-5 2-6 2-7 We have seen in previous units that climate models can give simulations of past as well as present and future climates. But we dont have temperature measurements going back more than about 150 years, so we rely on proxy measurements of temperature and precipitation to provide evidence climatic conditions hundreds and thousands of years ago. This will allow us to test climate models for accuracy and also offer a better perspective of current climate conditions and how much they might be expected to change if the future were to be similar to the past. 2-8 2-9 2-10 2-11 A brief overview of the locations and capabilities of and different type of measurements made by satellites will provide an understanding of different images and datasets on the ocean, land, clouds, atmosphere, and ice that have been given in previous units. 2-8 To provide a basis for evaluating the quality of climate models described in previous units and to understand the impact of changes in precipitation and temperature to be discussed in block 3 we need very complete and accurate long term measurements of the temperature and precipitation across the Earth. This unit provides information relating to the amount and quality of these measurements. 3-1 Increase in global human population is the root cause of recent changes in atmospheric chemistry and land use that we have discussed in previous units. Estimates of future changes in these environmental conditions depends on projections of future global human populations as described in this unit. 3-2 Economic advancement and enhanced living conditions in industrialized societies have been achieved through increased consumption of energy. But this increased use of energy has been the cause of changes in atmospheric chemistry as discussed in Block 1. And as other nations with very large populations, such as China and India, aspire to economic advancement they will likely contribute proportionally more to future changes in these environmental conditions. 3-11 We have seen in previous units on population, energy consumption, and the carbon cycle that our current rate of total global energy consumption cannot be sustained without significant changes to our global environment. So what needs to be done to develop policies and practices of energy and material use that are sustainable? 3-4 Changes in climate as discussed in Block 2 have different effects on different components of ecosystems: some species thrive while others find conditions less favorable. Some species will be lost. This unit addresses issues of whether these changes in biodiversity are critical to sustainable development as discussed in this Block. 3-9 This unit interprets changes in global climate as discussed in Block 2 in terms of changes that can be estimated for agricultural production in various countries. 3-3 This unit interprets changes in ozone, ultraviolet radiation, and global climate as discussed in Blocks 1 and 2 in terms of impact on human health. These impacts will provide basic information on which changes in public policy, as described in the unit on legislation, can be made. 2-5 In Block 3 we will want to assess the impact of climate change on agriculture in various countries and on water resources within countries. Global models, as described in previous units in this block, do not provide the level of detail needed for such assessments, so the discussion in this unit will give an overview of methods to narrow the range of uncertainty left by global models. 3-10 In Block 2 we saw that observations of both the recent and distant past reveal wide fluctuations in global patterns of precipitation. And climate models suggest future climates also will include changes from current conditions. In this unit we examine how such future climates will impact water resources, an increasingly critical element in societies with increased population and improved living standards. 2-10 Observations originally made by satellite have allowed us to observe that significant changes occur in ocean temperatures from year to year. As we discussed, atmospheric conditions respond quickly to changes in heating or cooling at the Earths surface, particularly over oceans. In this unit we look at how satellites are used to measure sea-surface temperatures and how these conditions relate to short term weather and logn-term climate change. 3-13 Local environmental changes linked to changes in global climate can give citizens a sense of helplessness because no one locally is to blame. 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