Albedo: Its effects on global warming in Polar Regions Presented by Morton Sternheim.
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1 Presented by Morton Sternheim Albedo:Its effects on global warmingin Polar RegionsPresented by Morton Sternheim
2 Big IdeaWhy are Polar Regions more affected by global warming than other parts of the globe?One reason (there are others) is that as sea ice melts and more open water appears, more energy is absorbed, and warming accelerates.This is a form of positive feedback and it makes the polar climate change faster than the climate in temperate areas.Increasing vegetation on land also has a similar positive feedback effect.
3 AlbedoThis effect is a change in the albedo – the fraction of the incident sunlight that is reflected back to space.The albedo is much higher for snow and ice than for water. Fresh snow can have an albedo as high as This is why skiers wear dark glasses. Ice and old snow typically have albedos from 0.2 to 0.45.However, liquid water has an albedo of only 0.03 for light incident at right angles to the water, and the albedo remains small until light comes in almost at a grazing angle. At 70 to the vertical or an altitude of 20, it is only about So even though sunlight reaches Polar Regions at low angles, it is mostly reflected by the ocean.
5 ExamplesA black car is much hotter to the touch than a white car in the summer sun.If you clear the snow from a patch of dark colored driveway, the adjoining snow melts faster than snow further away.The driveway absorbs more solar energy and heats the nearby snow, speeding up the melting process.
6 How does the albedo of north Africa compare with that of the southern part? What is the reason? At what time of year to the southern oceans have the higher albedo? The Arctic?
7 MicroclimatesPlaces where temperature, dampness, or wind velocity differs from surrounding areaDue to hills, rocks, crevices, depressions, colors, nearby water ….South facing slopes are warmer in northern hemisphereFrom many meters to millimetersContributes to diversity in tundra
8 Microclimates, cont.In a microclimate, very small changes can make a big difference to survival.Only a few centimeters above the ground, temperature and humidity can vary widely due to the sun's height, exposure to direct rays, and radiation reflected from the ground and atmosphere.Within millimeters of the surface, sheltered plants and invertebrates may not even be affected by a strong wind.
9 Temperatures vary with differences in slope, direction, and composition of surfaces Warmth from a plant melts nearby snowA windswept sastrugi with rippled surfaces provides sheltered spaces between the ridges
10 Cracks in hummocks provide warm shelters for small plants and animals in the tundra.
11 Typical Albedos (approx.) Fresh snow0.8 – 0.9Bare soil0.17New concrete0.55Worn asphalt0.12Desert sand0.40New asphalt0.04Green grass0.25Conifer forest (summer)0.08See Wikipedia for sources
12 How Can We Measure Albedo? Pyranometer – measures temperature of a dark absorbing material, pointing alternately at surface and sky. ExpensiveWikipedia photo
13 How Can We Measure Albedo? Light meters – fast, easy to use, inexpensive. Same principle.LED’s and multimeters. Use LED as detector rather than a source.Digital camera and free imaging software (ImageJ) – compare reflected light from surfaces. Free given a camera, computer.
14 How Can We Study Microclimates? Measure temperatures at various sites with thermometersMeasure temperatures of objects with different colors and inclinations with heat lampsThis helps students to understand the absorption of sunlight does raise the temperature.
15 Albedo & Angle of Incidence Experiments Many variations of heat lamp experimentsVary angle, measure temperature changes over timeVary color, measure temperature changesSee a simple version with paper plates on the IPY materials pageAlso, you can make “pockets” out of colored construction paper, insert thermometers (Sandy Johnson)Wayne Kermenski, Mohawk Trail15
16 The Sun’s Radiation Spectrum ~ 43% of energy is in the visible range~ 49% in near infrared range~ 7% in ultraviolet range< 1% in x-rays, gamma waves, and radio waves.Source: Adapted from
17 A CaveatLight meters designed for illumination measurements (and most digital cameras) only detect visible light.Light meters are also designed to be most sensitive to green light, matching sensitivity of human eye.The fraction of the light that is reflected may depend on the frequency.Thus albedo results from a light meter (or digital camera or LED) may not be really accurate.
18 Light MeterMastech Digital 4-Range 200,000 Lux Luxmeter, LX1330B, Sold by: Kaito Electronics, Inc$ shipping from Amazon.com4 ranges, lux or ft-candles; ± 3% accuracy.Lux – measures intensity of light per unit area, weighted according to human brightness perception
19 Typical Lux Values Brightest sunlight 200,000 lux Well lit office Full moon0.25 luxMinimum value for meter0.1 lux
20 Three Experiments Today Measuring albedo with light metersMeasuring soil temperatures with thermometersDigital camera and free imaging software (ImageJ) – compare reflected light from surfaces.There are other experiments to measure albedo and angle of incidence effects