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Midterm Review. CLIM 101: Weather, Climate and Global Society. Question 1.
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Midterm Review CLIM 101: Weather, Climate and Global Society
Question 1 (25 points) The Earth’s climate has changed dramatically over the billions of years that the planet has been in existence. One characteristic fluctuation has been the variation over tens of thousands of years from cold, heavily glaciated periods to warm, relatively ice-free states. Identify the proximate and ultimate causes of the glacial-interglacial cycle.
Question 1 Definitions: Proximate cause: an event or process which is closest to, or immediately responsible for causing, some observed result Ultimate cause: the "real" reason something occurred Ice Ages: Proximate cause: The Earth’s climate has cooled and warmed, at long (~100 ka) intervals, sufficiently to permit large ice sheets to form. An ice-albedo positive feedback amplified this effect to allow the ice sheets to grow to huge extents over most of the Northern Hemisphere land masses Ultimate cause: The Earth’s orbit around the Sun is not constant, but varies in eccentricity, obliquity and by precession of the equinoxes, causing the amount of solar energy reaching the Earth to vary widely, which, in turn, cools and warms the mean climate of the planet
Question 2 (20 points) For each of the following land-use changes, indicate whether the change would increase or decrease the albedo of the land and a one-sentence explanation why. • A forest is clearcut, leaving exposed soil • Replacing wheat fields with a forest • Paving wheat fields to make a parking lot • Painting the roof of an office building white
Question 2 • When a forest is clearcut, leaving exposed soil, the albedo increases, because grassland is brighter than forest, so it scatters more solar energy • Replacing wheat fields with a forest decreases albedo, because forest is darker than wheat fields • Paving wheat fields to make a parking lot decreases albedo, if the parking lot were paved with asphalt; it might increase if the parking lot were paved with concrete • Painting the roof of an office building white increase albedo, because a white roof is brighter, in general, than typical roofing materials used in office buildings
Question 3 (20 points) The recent era of Earth’s history is called “Anthropocene” because humans have had a significant global impact on climate and ecosystems. Below are possible examples of interactions among humans, climate and ecosystems. For each one, indicate the nature and direction (cause effect) of the relationship and why the two are related*. • Greenhouse gas concentrations :: energy use by humans • Forest clearcutting :: surface albedo • Total food grain production in India :: Indian monsoon rainfall • Rapid population growth :: economic development • * For example, in the relationship, baseball games won :: runs scored we would say that higher run production usually results in more games won, because scoring more runs is necessary to win games.
Question 3 • Greenhouse gas concentrations are increased (effect) by energy use by humans (cause), because most energy used by humans requires the burning of fossil fuels and the combustion of fossil fuels releases carbon dioxide and other greenhouse gases into the atmosphere. • Forest clearcutting causes surface albedo to increase (effect), because forests are darker than grasslands that typically replace them when they are cut down. • Total food grain production in India (effect) is directly related to Indian monsoon rainfall (cause) - more rainfall allows more grain production. HOWEVER, there can be too much of a good thing - excessive rainfall can produce flooding that destroys crops. Also, clearcutting forest for grain fields can alter the distribution of rainfall, although this is less of a factor in a monsoon region. • Population growth and economic development are directly related. As population grows, economic development is faciliated by the availability of labor. As the economy develops, a larger population can be sustained. HOWEVER, rapid population growth (cause) can hinder economic development (effect), because the burgeoning population cannot be engaged in economic development fast enough, and the strain on the economy of a developing nation to provide for its population limits the possible directions of development.
Question 4 (20 points) Answer each question below in 1-2 sentences. • Why do scientists adopt various scenarios for greenhouse forcings? • How are the scenarios used in climate models? • Does the use of different scenario increase or decrease confidence in projection of global climate change? • Describe the likely change in incidence of heat waves for scenarios B1 and A2. Are they different? How?
Question 4 • Why do scientists adopt various scenarios for greenhouse forcings?Various scenarios are used to conduct “what if” exercises that can estimate the consequences of various socioeconomic development paths. • How are the scenarios used in climate models? In the AR4, scenarios were used to estimate the concentrations of greenhouse gases, which were then specified as input to climate models. The models were used to simulate the evolution of the climate in response to the presumed scenarios of greenhouse gas concentrations.
Question 4 • Does the use of different scenario increase or decrease confidence in projection of global climate change? On the one hand, using different scenarios introduces uncertainty, because it is not perfectly well known how the world economies will develop in the future. On the other hand, the different scenarios provide a way of bracketing the climate system response to various possible futures for human society, thereby increasing the confidence that the full range of possible futures has been accounted for.
Question 4 • Describe the likely change in incidence of heat waves for scenarios B1 and A2. Are they different? How? Scenario B1 is a “green” future with de-materialization and introduction of clean energy technologies, while A2 is a future in which countries go it alone and depend on local traditions. Therefore, scenario B1 leads to moderately increasing and eventually decreasing greenhouse gas concentrations, while scenario A2 leads to ever-increasing greenhouse gas concentrations as countries fail to recognize the threat and rein in emissions.
Probability Density Function for Global Mean Temperature Changes
Question 4 • Describe the likely change in incidence of heat waves for scenarios B1 and A2. Are they different? How? Scenario B1 is a “green” future with de-materialization and introduction of clean energy technologies, while A2 is a future in which countries go it alone and depend on local traditions. Therefore, scenario B1 leads to moderately increasing and eventually decreasing greenhouse gas concentrations, while scenario A2 leads to ever-increasing greenhouse gas concentrations as countries fail to recognize the threat and rein in emissions. As a result, we can expect the warming to be much greater in scenario A2 than in scenario B1. Because the warming will shift the distribution of temperatures to higher values in many areas, we can expect the incidence of heat waves, including extreme, deadly heat waves, to increase much more in the case of scenario A2 than for scenario B1.
