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

Albedo:Albedo:Its effects on global warming

in Polar Regions

Presented by Morton SternheimPresented by Morton Sternheim

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. Fresh snow can have an albedo as high as 0.95. 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 0.1. So even though sunlight reaches Polar Regions at low angles, it is mostly reflected by the ocean.

Albedo of Water

http://en.wikipedia.org/wiki/Image:Water_reflectivity.jpg#file

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.

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?

http://isccp.giss.nasa.gov/products/browsesurf1.html

Microclimates• Places where temperature, dampness, or

wind velocity differs from surrounding area

• Due to hills, rocks, crevices, depressions, colors, nearby water ….

• South facing slopes are warmer in northern hemisphere

• From many meters to millimeters

• Contributes to diversity in tundra

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.

Warmth from a plant melts nearby snow

Temperatures vary with differences in slope, direction, and composition of surfaces

A windswept sastrugi with rippled surfaces provides sheltered spaces between the ridges

Cracks in hummocks provide warm shelters for small plants and animals in the tundra.

http://www.arctic.uoguelph.ca/cpe/environments/climate/causes/microclimates.htm

Typical Albedos (approx.)

Fresh snow 0.8 – 0.9 Bare soil 0.17

New concrete 0.55 Worn asphalt 0.12

Desert sand 0.40 New asphalt 0.04

Green grass 0.25 Conifer forest (summer)

0.08

See Wikipedia for sources

How Can We Measure Albedo?Pyranometer – measures temperature of a dark absorbing material, pointing alternately at surface and sky. Expensive

Wikipedia photo

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.

How Can We Study Microclimates?

• Measure temperatures at various sites with thermometers

• Measure temperatures of objects with different colors and inclinations with heat lamps– This helps students to understand the

absorption of sunlight does raise the temperature.

Albedo & Angle of Incidence Experiments

• Many variations of heat lamp experiments

• Vary angle, measure temperature changes over time

• Vary color, measure temperature changes

• See a simple version with paper plates on the IPY materials page

• Also, you can make “pockets” out of colored construction paper, insert thermometers (Sandy Johnson)

http://sites.google.com/site/climatechangecurriculum/home Wayne Kermenski, Mohawk Trail

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 http://www.ucar.edu/learn/imgcat.htm

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 or LED) may not be really accurate.

Light Meter

• Mastech Digital 4-Range 200,000 Lux Luxmeter, LX1330B, Sold by: Kaito Electronics, Inc

• $54.95 + 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 sunlight 200,000 lux

Well lit office 400 lux

Full moon 0.25 lux

Minimum value for meter 0.1 lux

Three Experiments Today

1. Measuring albedo with light meters

2. Measuring soil temperatures with thermometers

3. Digital camera and free imaging software (ImageJ) – compare reflected light from surfaces.

There are other experiments to measure albedo and angle of incidence effects

Measuring Albedo with ImageJ