Session #2, CLASS NOTES.Relevant reading: Chap 1, p.1-10; Chap 4, p.69-72Three major global problems. We discussed three major global problems due to theactivities of humankind:(1) Global warming(2) Ozone depletion(3) Biodiversity loss (primarily a result of deforestation)#1 Global Warming and the Greenhouse Effect Notes:The surface of the Earth is warmed by sunlight (also known as solar radiation). Certaingases in the atmosphere absorb heat radiation (infrared radiation) coming from the warmplanetary surface and this causes the atmosphere itself to warm up to some finitetemperature. The atmosphere then gives off infrared radiation because it is at a finitetemperature. Some of the atmosphere’s infrared radiation goes down back to the surfaceof the Earth and warms the surface. Consequently, the Earth’s surface is warmer than itwould be if there were no atmosphere because it is heated from two sources: (1) radiationfrom the Sun AND (2) radiation from the atmosphere. If there were no atmosphere, theEarth’s surface would only be heated by the Sun, so the Earth would be much colder. Themechanism by which a planet’s atmosphere heats a planet’s surface is called thegreenhouse effect. The greenhouse effect warms the Earth’s surface by about 33°C. Thecurrent mean global temperature is 15°C, so if we did not have the greenhouse effect ofthe Earth’s atmosphere, the mean global temperature would be –18°C, i.e. well belowfreezing.Greenhouse gases are those gases in the atmosphere that absorb infrared radiation andradiate some of it back down to the surface, thereby warming the surface. Globalwarming is a warming of the Earth’s atmosphere due to human-induced enhancement ofthe greenhouse effect.Greenhouse gases include carbon dioxide, CO2. Carbon dioxide is produced by humans,who burn fossils fuels (coal, oil, natural gas). Deforestation also contributes to CO2increases because dead trees decay and make CO2 during decay. Other greenhouse gasesinclude methane (CH4), nitrous oxide (N2O), and certain chlorofluorocarbons.Chloroflurocarbons (CFCs) are so called because they contain chlorine (Cl), fluorine (F)and carbon (C). CFCs are also known as freons. Examples of CFCs include CCl3F andCCl2F2. Water vapor (H2O) is also an important greenhouse gas, but the concentration ofwater vapor in air is variable and depends on the temperature of the atmosphere. Forexample, when it is cold, the atmosphere can contain little water vapor and watercondenses out (witness your breath on a cold day). So water vapor levels are driven by anatmospheric temperature that is set, in turn, by the other main greenhouse gas, CO2.#2 Ozone depletion notes.For now, note that ozone molecules are made up of three oxygen atoms (O3), which isdifferent from oxygen molecules made up of two oxygen atoms (O2). The peakconcentration of ozone is about 25 km altitude above where we live.#2 Biodiversity notesWe need to define biodiversity. We define it as the number of species in a given area. Forexample, it could be the total number of animal and plant species in a given area.Alternatively, we might just be considered with bird biodiversity, say – the total numberof bird species in a given area.What is “climate”? How does it differ from “weather”?If we’re to discuss “climate change” we need to understand what we mean by “climate”.The difference between weather and climate is that between instantaneous conditions andaveraged conditions. We define climate as "the characteristic pattern of weather over aregion and over a period of time." For example, the average monthly temperature forJanuary in western Washington indicates the climate during a particular period over aspecific region. We could also average other weather elements, such as temperature,rainfall, humidity, sunshine, wind, etc., to get a broader sense of the climate conditionsduring a particular period. However, on any particular day, we might get a temperature(or rainfall, humidity, etc.) that is higher or lower than the historical average. Thusclimate is “what you expect” and weather is “what you get”.In class, we compared Fig 4.18a,b & c that show temperatures across the world andindicate summer and winter climates. Primarily, the climate is driven by the latitudinaldistribution of sunlight (see Fig. 4-15, p.67, and associated write-up). However, the worldis complicated. Land/ocean contrasts, altitude/topography, and atmospheric and oceancurrents all play a role in setting the climate in a particular region. Continents have alarger variation in temperature between summer and winter than oceans. Tropical oceans,for example, have little variation in temperature between summer and winter (see Fig4.18). At altitude it is generally colder and wetter/snowier. Ocean currents can alsomodify temperatures, e.g. the Gulf Stream moderates the temperature in wintertimecoastal western Europe.The Earth SystemA key theme is that the Earth system behaves as a “coupled system”. This is a system ofcomponents that interact with each other and affect one another. The Earth system is nota single entity but made up of an ocean, atmosphere, biosphere and solid planet. Each ofthese, in turn, is made up of components, e.g. the atmosphere can be thought of ascomposed of a number of weather systems, a water cycle, and so on.In discussing systems, we often talk of “forcings”. In the textbook (p.3-4), it says:“One of our goals is to show how the different components of the Earth system interact inresponse to various internal and external influences, or forcings.” What do we mean bythe term “forcing”? Forcing is a persistent disturbance to a system. Forcing imposes achange on one or more components of the Earth system, e.g., the variation of sunlightover a year on the planet drives the climatic temperature, which in turn, affects thecycling of water. When we are dealing with systems as complicated as the Earth, it is notalways simply a matter of cause and effect. Global warming might change oceancurrents, for example, that could change the exchange of greenhouse gases between theatmosphere and ocean, and cause more global warming. This is an example of feedback.Also we often think of cause and effect as an immediate linear response. However,systems can also have delayed responses and abrupt changes (or nonlinear response). Forexample, when you boil some water, it takes time to reach a transition point whereconvection cells and bubbles