Metr 112: Activity 5 Due: Sunday, June 25th, 2017 (at 11:59 P.M.) Submit electronically via Canvas (.doc, .docx, or .pdf file format). Email or see me in office hours if you have questions. Please answer all questions in complete sentences. Imagine that the Earth was to warm for some reason (initiating mechanism or forcing). 1. Identify two positive feedbacks that would influence the earth’s climate and explain how each one works. Use 4-6 sentences for your response. (4 points) 2. Identify two negative feedbacks that would influence the earth’s climate and explain how each one works. Use 4-6 sentences for your response. (4 points) 3. Which of the feedbacks you identified do you think is most uncertain? Explain your reasoning in 3-5 sentences. (2 points) METR 112 Global Climate Change - Lecture 5 Natural Forcing Factors Henry Bartholomew (M.S.) San Jose State University ▪ Reading: Chapter 3, pages 45-54 1 Class Meeting ▪ Watch the video for this lecture at: https://www.youtube.com/watch?v=bUqhpaC_C2E 2 3 Global temperature change over past 18,000 years 4 Natural Climate Change ▪ External Forcing Factor – The agent of change is outside of the EarthAtmosphere system ▪ Internal Forcing Factor – The agent of change is within the EarthAtmosphere system itself 5 External Forcing Factors ▪ Variations in solar output ▪ Orbital variations ▪ Meteors 6 Internal Forcing Factors ▪ Volcanoes ▪ Plate Tectonics ▪ Changes in atmospheric composition 7 Solar Variations ▪ Sunspots correlate with solar activity  More sunspots, more solar energy 8 Figure 3.15 Sunspots Sunspots ▪ Caused by periodic changes in alignment between sun’s rotational axis and gravitational center of solar system ▪ Produces intense fluctuations in magnetic field of sun ▪ Temperatures of 3500-4500 K (5840-7640ºF) ▪ Surrounding regions: 5500 K (9440ºF) ▪ Sunspots appear darker due to lower intensity of radiation emitted 10 SOLAR ACTIVITY ▪ Sunspots are the most familiar type of solar activity. 11 12 THE SOLAR CYCLE ▪ Sunspot numbers increase and decrease over an 11-year cycle ▪ Observed for centuries. ▪ Individual spots last from a few hours to months. ▪ Studies show the Sun is in fact about – 0.1% brighter when solar activity is high. 13 Figure 3.16 Number of sunspots THE MAUNDER MINIMUM ▪ An absence of sunspots was well observed from 1645 to 1715. ▪ This so-called “Maunder Minimum” coincided with a cool climatic period in Europe and North America: “Little Ice Age” ▪ The Maunder Minimum was not a unique occurrence 15 Orbital changes ▪ Milankovitch theory: ▪ Serbian astrophysicist, who during the 1920’s, studied the effects of solar radiation on the irregularity of ice ages ▪ Variations in the Earth’s orbit – Changes in shape of the earth’s orbit around sun: Eccentricity (100,000 years) – Wobbling of the earth’s axis of rotation: Precession (21,000 years) – Changes in the tilt of earth’s axis: Obliquity (41,000 years) 16 If the earth’s tilt was to decrease, how would the summer temperature change at our latitude? 1. Warmer summer 2. Cooler summer 3. Summer would stay the same 4. Impossible to tell 17 Earth’s orbit: an ellipse • Perihelion: place in the orbit closest to the Sun • Aphelion: place in the orbit farthest from the Sun 18 http://www.indiana.edu/~geol105/images/gaia_chapter_4/milankovitch.htm Figure 3.12 Precession of Earth’s solar orbit Figure 3.12 Precession of Earth’s solar orbit (Part 1) Figure 3.12 Precession of Earth’s solar orbit (Part 2) Figure 3.8 Obliquity Figure 3.9 Influence of orbital variations on solar insolation and historical temperature changes of the orbit (Part 1) Temperature: the last 400,000 year From the Vostok ice core (Antarctica) 26 Formation of Glaciers ▪ Glaciers - composed of fallen snow that is compressed into a large, thickened mass of ice over many years ▪ Glacier Growth: When yearly snowfall (winter) is greater than snowmelt (summer) ▪ Glacier Decay: When yearly snowfall (winter) is less than snowmelt (summer) 27 Perito Moreno Glacier in Argentina 28 High summer sunshine, lower ice volume 29 Glaciers and Seasonal Strength ▪ Milankovitch proposed that when solar insolation in the Northern Hemisphere was relatively high during December and January (warmer winter), and relatively low during June and July (colder summer), more snow accumulated during the winter and less melted during the summer, causing glaciers to advance. 30 Activity Consider the fact that today, the Perihelion of the Earth’s orbit around the sun occurs in the Northern Hemisphere winter. In 10,500 years, the Perihelion will occur during Northern Hemisphere summer. A) Explain how the climate (specifically, temperatures in Winter and temperatures in Summer) of the Northern Hemisphere would change in 10,500 years, just due to precession. B) How would this affect the presence of Northern Hemisphere glaciers (grow, decay, or stay constant)? 31 Eccentricity ▪ When earth’s orbit around the sun is more elliptical, the effects of Perihelion and Aphelion on seasonality are higher 32 Internal Forcing Factors ▪ Volcanoes ▪ Plate Tectonics ▪ Changes in atmospheric composition 33 Volcanoes 34 Plate Tectonics 35 Changes in atmospheric composition 36
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