Lecture week of 5-10 - Notes Climate Biomes and Biosphere PDF

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Biol 114 Spring 2021 Lecture Week 14 Climate, Biomes and the Biosphere I. Introduction Before we leave the Ecosystem level of the biological hierarchy, we must expand our use of the level. More specifically, we need to discuss Biomes. Biomes are areas distinguished primarily by their predominant plants and are associated with particular climates. They consist of distinctive plant formations such as the tropical rainforest biome and the desert biome. Biomes are placed around our planet in specific areas. Meaning, biomes do not occur randomly around the globe. In order to best understand this, we must consider the last 2 levels in our hierarchy together: ecosystems and the Biosphere. The biosphere is the living part of our planet. All that comes in is sunlight energy. All that goes out is heat energy. Everything else, good or bad, stays here. To begin our understanding of biome placement we must first discuss Climate and what causes climate. In order to understand climate we must first consider sunlight more stringently than what we have done in the past. Thus far we have only considered sunlight as the energy source for plants in photosynthesis. We now need to consider it also as a source of heat for the planet. II. Light A. Electromagnetic radiation – sunlight 1. Basic unit of sunlight is the photon, a packet of energy that travels as a wave. These waves have lengths (wavelength - distance from successive peak to peak) and frequency (number of peaks passing a fixed point per unit time) 2. Since the speed of light is a constant, the frequency is related to the wavelength in that shorter wavelengths have greater frequencies, and longer wavelengths have lower frequencies. 3. The wavelength (and frequency) of electromagnetic radiation is determined by the amount of energy in the photon - greater energy causes shorter wavelengths 4. All bodies with a temperature above absolute zero (just zero on the Kelvin scale) radiate energy: the higher the temperature, the greater the energy, and the shorter the wavelength, of photon is emitted.

Case Study: Consider an iron bar in a blacksmith's furnace. As it heats it begins to give off visible radiation. It starts to glow red and, as it heats more, it glows with a white light. There are some lessons to be learned here. B. Visible light 1. (First lesson) Why red first? Heating is not uniform throughout the rod, and each region emits photons directly related to the temperature at that spot. Red light has the longest wavelength of visible light and so, as the iron heats, the hottest

areas will appear red, the first wavelengths of electromagnetic spectrum we can detect with our eyes. As the rod continues to heat, more areas are hot enough to emit visible radiation but, once again, the actual temperature is not uniform and so we get a wide range of photons with wavelengths in the visible spectrum and we perceive the overall effect as white light, since there is no one wavelength of light that is white. 2. (Second lesson) Objects with the temperature of our sun emit most of their radiation in the visible spectrum. This is not a coincidence. We evolved eyes to detect light at these wavelengths as they dominate the spectrum available to us because we are close to the sun. Note that we do not detect all of the common wavelengths given off by the sun. We do not see ultraviolet, which has wavelengths shorter than the shortest we can see. Other organisms (not just animals!) can detect these but we name the visible spectrum for what humans can see, not for what all living organisms can see. A collective name for the radiation given off by the sun is shortwave radiation (from about 100 to 2000 nanometers). A subset of shortwave radiation (roughly the same as visible radiation) is used by photosynthetic plants, algae, and bacteria to power photosynthesis. These wavelengths are referred to by biologists as PAR (Photosynthetically Active Radiation). C. Non-visible light 1. (Third lesson) Radiation is emitted by the rod before we can see it glow. In fact, radiation is emitted from all objects, including you. However, the wavelengths emitted by you are too long for our eyes to detect. When special cameras that do detect at our emitted wavelengths are used, we do glow. This is the basis of night vision cameras and glasses. Images are made from the glow of objects that emit in the Infrared range of wavelengths, and translated into wavelengths that we can see by the night vision apparatus. 2. (Fourth lesson) Infrared means below red. Thus, it is radiation with wavelengths below our power to detect as the photons do not have sufficient energy to initiate the physiochemical reactions we call vision. This is the range emitted by objects at the temperatures we have on Earth and so we also refer to this as Thermal Radiation. 3. Radar, radio, TV, and cell phones use radiation with wavelengths longer than what is in the range of infrared (up to hundreds of meters long). 4. Gamma ray and X-ray radiation have shorter wavelengths (and thus higher energy) than the radiation discussed here and can have wavelengths as short as a millionth of a nanometer. D. Light as heat and the Global Heat Budget

1. Recall that heat is kinetic energy, the energy of moving and vibrating atoms and molecules. Temperature is determined by the average speed of that motion (e.g. hotter gasses and liquids have faster moving molecules). Electromagnetic radiation is converted to heat when photons are absorbed by atoms and move faster as a result (we measure this as heating). Heat energy is converted to electromagnetic radiation when a photon is emitted by a moving atom that slows as a result of the loss of energy (we measure this as cooling). 2. The sun contributes almost all of the energy that drives climate and, ultimately, living systems. The sun's contribution is in the form of electromagnetic radiation. Earth receives energy as photons from the Sun. The energy balance at the surface of the Earth is result of losses to space and the incoming radiation from the Sun. Thus, we can do a budget, just like a household budget is the record of income and expenditures. The global budget is complicated by the fact that Earth is surrounded by an atmosphere. 3. The atmosphere is densest at the surface of the Earth because gravity pulls the molecules of gas toward the center of the Earth. Gravity is resisted by the speed at which the molecules move (their temperature). So the atmosphere is thickest at the surface and becomes thinner as you ascend. But, the temperatures found as you ascend change abruptly and this separates the atmosphere into four general layers. E. Atmosphere (Details are added for completeness. Be sure to know the layers and general concepts that make the layer unique.) 1. Troposphere - surface to about 8 km at the poles and to about 17 km at the equator. The air cools as you go up at a rate of about 6.5°C per kilometer for 12 km but then stops cooling. This is the layer of most clouds and precipitation. The average temperature of the surface of the Earth is about 15°C and the tropopause (top of the troposphere) is about -60°C. 2. Stratosphere - from tropopause to Stratopause at about 50 km up. The stratosphere warms as you go up because oxygen is absorbing the sun's energy and heating the layer (from -60°C to about -10°C). The upper is hotter because it gets more input from the sun but the lower layers are somewhat shaded by the upper layers. The stratosphere is where we fly large airplanes and there are two important climatic factors in this layer. a. Ozone Layer - as Oxygen absorbs sunlight, the energy of the photons can do one of two things. They can cause the molecules to speed up (increasing their temperature) or they can be absorbed by electrons: including those involved in the O2 bond. This addition of energy makes the oxygen molecules reactive and some break apart. The singlet oxygens are highly reactive and, if they happen to bump into oxygen gas molecules, ozone (O3) molecules are formed. Ozone is important because

it absorbs ultraviolet radiation and the layer in the Stratosphere greatly reduces the amount of UV that reaches organisms at the surface. UV, of course, can break chemical bonds and wreaks havoc with complex organic molecules like proteins and DNA. b. Jet Streams - these occur at the lower areas of the stratosphere and are currents of air that move very fast (some over 300 kpm). The jet streams cause movement in the troposphere and affect the movement of the high and low pressure areas of the troposphere we follow on the weather forecasts. 3. Mesosphere - from stratopause to the Mesopause at about 100 km. This is an area of cooling gasses whose temperatures drop from -10° to -100°C through ascension. However, at the mesopause, the upper boundary of the mesosphere, the temperature begins to rise again. 4. Thermosphere - from mesopause until the atmosphere becomes too thin to measure, over 3000 km up. It heats because nitrogen and oxygen are maximally exposed to the sun and they can heat up to temperatures over 2000°C. However, the atmosphere is so thin here that the amount of energy involved is not very great and, were you to be exposed to it, it would not feel like exposure to such a temperature at the surface of the Earth. Thus, our atmosphere is a very complex boundary between the surface of the Earth and space and its presence is vital to creating the conditions suitable for life at the surface. F. Earth’s energy budget (associated units are for balancing and relative proportions only. Do not memorize these values) 1. At the surface of the Earth, energy is received from two sources. a. Sun (51 units) and b. Thermal radiation from the atmosphere (96 units). 2. Energy is lost through three processes. a. Evaporation (23 units) - evaporation is the loss of faster moving water molecules from a larger body of water. As they leave, they become part of the atmosphere and the energy of their motion is lost from the surface of the Earth. (Think evaporating water from your body cooling you as you step out of the shower.) b. Convection by the atmosphere (7 units). Heat energy is transported either through Conduction (transfer of heat energy from molecule to molecule in a solid), Radiation (conversion to photons and loss through space) or Convection (transfer to molecules in a fluid - either gas or liquid). Air is heated by the Earth and expands, which decreases its density, and it rises as cooler, denser air displaces it at the surface. This convection constitutes a loss of energy from the surface of the Earth.

c. Thermal radiation (117) - The infrared "glow" of the Earth's surface is a loss of energy d. As you can see, the largest flow of energy is thermal radiation (117units from the Earth, where 96 units are radiated back from the atmosphere 3. The 96 units from the Atmosphere is what we refer to as the Green House Effect as gasses in the atmosphere absorb thermal radiation from the Earth and return most of it to the surface. Our effect on the concentration of greenhouse gasses is the basis of the worries about global warming. 4. Note that the budget is balanced at the surface (51+96=147 units of energy gained and 23+7+117=147 units lost as thermal radiation). III. Climate Patterns Climate is the long-term pattern of weather in a locality, region, or even over the entire globe. Weather is the temperature and moisture conditions for a specific place and time. They differ in scale in both space and time. Note that, unlike many definitions of weather, there is no mention of averages. This is not to exclude averages from the description of climate, as they are important descriptors. The reason for not mentioning average in the definition is that averages are not sufficient to describe climate. Maximum and minimums are also important. Extreme events may also be important as well. For example, hurricanes are very important components of the climate of southern Florida but they do not affect long-term averages very much. Investigation: Why are there seasons? A. Due to Earth’s orbit, sometimes Earth is closer or farther away from the sun. 1. Earth’s orbit is elliptical, and is different distances from the sun at different times of the year. This distance varies by 3 million miles annually 2. Is there correspondence between distance and season (e.g., winter)? a. Distance is greatest in month of b. Distance is least in 3. What is your conclusion?

B. Due to Earth’s tilt on its axis, some places on Earth are closer or farther from the sun. 1. How much does distance between Earth and Sun change with tilt? 93 million miles.

2. Width of Earth is 7,926 miles 3. ~ (7,926/93,000,000) x 100 < 0.01%. So change with tilt is very tiny! 4. What is your conclusion?

C. Due to the shape of Earth and tilt on its axis, some places receive less sunlight per unit area at some times of the year. 1. The curvature of Earth spreads light beams as they come in from the sun. Energy from sunlight is greater per unit area where beams are not spread, as compared to those areas where the light is spread. This is called “differential heating” across Earth’s surface. 2. The tilt of Earth on its axis also plays a part in determining where the beams of sunlight are most and least spread. a. During spring and fall, the least spread of light beams occurs at the equator. b. During summer in the Northern Hemisphere, the least spread of beams occurs at 23° N latitude, referred to as the Tropic of Cancer. So the greater spread is in the Southern Hemisphere. c. During winter in the Northern Hemisphere, the least spread of beams occurs at 23° S latitude, referred to as the Tropic of Capricorn. So the greater spread is in the Northern Hemisphere. 3. What is your conclusion?

D. What causes wind and precipitation? 1. Hot air rises, creating movements of air masses. As air rises, it leaves behind a low-pressure area below it. This low pressure area is surrounded by air masses that are of relatively higher air pressure. The only way in which air can move is from areas of higher pressure to areas of lower pressure. Therefore, the low pressure area left underneath the rising air mass is filled with air coming from the relatively higher pressured air surrounding it. We feel this as surface winds. 2. Air masses near the surface of the Earth are relatively moist. As this moist air heats from exposure to sunlight, it rises. As the moist, warm air rises, it comes into contact with air that is cooler than itself. Why? 3. Cool air cannot evaporate water as quickly as warmer air can. (It is a common misconception that warm air can hold more moisture than cool air can. However, this is not true. Warm and cool air can hold the same amount of moisture. The difference, however, is in how quickly moisture can be

evaporated into the air. Warm air evaporates moisture into it more quickly than cool air can. The end result is still the same whether you believe warm air can hold more moisture than cool air can, or that there is no difference between the air masses.) Rising moist, warm air comes in contact with and mixes with cooler air. This mixture causes condensation (water coming out of the air and sticking to other water molecules). When enough molecules come together the combined weight cannot be supported by the local wind currents, and so precipitation occurs. 4. Intertropical Convergence Zone (ITCZ) – The process described in steps 1-3 above is most intense in those areas where sunlight is least spread on the globe (more specifically, the equator in the fall and spring). The ITCZ shifts from the equator to 23.5ºN in the summer of the Northern Hemisphere (winter of the Southern), back to the equator in the fall of the Northern Hemisphere (spring of the Southern), to 23.5ºS in the winter of the Northern Hemisphere (summer of the Southern)....