Albedo: Its effects on global warming in Polar Regions Presented by Morton Sternheim

 2008 Batom Inc.

Big Idea Why 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.

Albedo This 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

Snow and 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 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.

Examples A 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.

Painting black rooftops white in New York City might lower summer afternoon temperatures 2 ºF (NCAR, 2010)

Typical Albedos (approx.) Fresh snow0.8 – 0.9Bare soil0.17 New concrete0.55Worn asphalt0.12 Desert sand0.40New asphalt0.04 Green grass0.25Conifer forest (summer) 0.08 See Wikipedia for sources

Albedo of Water

How Can We Measure Albedo? Pyranometer – measures temperature of a dark absorbing material, pointing alternately at surface and sky. Expensive. Light meters – fast, easy to use, inexpensive Other options later

Light Meter Mastech Digital 4-Range 200,000 Lux Luxmeter, LX1330B, Sold by: Kaito Electronics, Inc $ shipping from Amazon.com 4 ranges, lux or ft- candles; ± 3% accuracy. Lux – measures intensity of light per unit area, weighted according to human brightness perception

Typical Lux Values Brightest sunlight200,000 lux Well lit office400 lux Full moon0.25 lux Minimum value for meter0.1 lux

Using the Light Meter Press POWER to turn on the meter. Use LUX/FC to select lux. Remove the photo detector cap and place the detector horizontally face up. Press RANGE to find a suitable range. Indoors, pointing up, you should get a 3 digit reading without an x10 or x100 indicator at the bottom In making measurements, pressing HOLD stops further measurements. Pressing HOLD again cancels the hold mode. Avoid casting shadows on surfaces when making measurements.

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

A Caveat Light 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) may not be really accurate.

How Can We Measure Albedo? 1.Light meters 2.LED’s – equivalent to meters 3.Digital camera and free imaging software (ImageJ) – compare reflected light from surfaces. Free given a camera, computer 4.Measure temperature changes - Children may not realize connection between albedo and heating –Effects of surface color using heat lamps; also angle of incidence effects –Measure temperatures with thermometers; study microclimates

At what time of year to the southern oceans have the higher albedo? The Arctic? How does the albedo of north Africa compare with that of the southern part? What is the reason? ducts/browsesurf1.html