METR112 Global Climate Change -- Lecture 2 Energy Balance and

Prof. Menglin JinSan Jose State University

Surface Albedo

Video Greenhouse Effect

___CO2, H20______ (CO2, H2O, N2, O2) in Atmosphere _____ (absorb, penetrate) solar energy, and _______ (absorb, penetrate) longwave surface energy. This ______ (extracting, leaving) longwave energy is called ______ (greenhouse effect, albedo effect)

Video: Global Ice Albedo

http://www.met.sjsu.edu/metr112-videos/MET%20112%20Video%20Library-MP4/energy%20balance-albedo/

Global Ice Albedo.mp4

Ice Albedo.mp4

Arctic sea ice coverage, 1979 and 2003 NASA http://www.learner.org/channel/courses/envsci/unit/text.php?unit=12&secNum=7

•The Earth is not warming uniformly. •Notably, climate change is expected to affect the polar regions more severely:•The Arctic is warming nearly twice as rapidly as the rest of the world; •winter temperatures in Alaska and western Canada have risen by up to 3–4°C

in the past 50 years, and •Arctic precipitation has increased by about 8 percent over the past century

(mostly as rain)

Positive albedo feedback

Due to, partly:

Higher surface temperature

Less snow

Smaller albedo

More insolation in surface

Albedo Definition

The ratio of the outgoing solar radiation reflected by an object to the incoming solar radiation incident upon it.

Earth Observatory GlossaryBy NASA,Responsible NASA official: Dr. Michael D. King,http://earthobservatory.nasa.gov/Library/glossary.php3?mode=all

IN OUTI I

α =IOUT

IIN

Albedo of Earth

•The term albedo (Latin for white) is commonly used to or applied to the overall average reflection of an object.

•the albedo of the Earth is 0.39 (Kaufmann 1991 ) and this affects the equilibrium temperature of the Earth.

•The greenhouse effect, by trapping infrared radiation, can lower the albedo of the earth and cause global warming.

This is why albedo is important This is why GHG is important

Features of Albedo

•Dimensionless

•Range: 0 (dark) – 1 (bright)

The word is derived from Latin albedo "whiteness", in turn from albus "white".

•Albedo depends on wavelength

•Albedo is determined by the structural and optical properties of the surface, such as shadow-casting, mutiple scattering, mutual shadowing, transmission, reflection, absorption and emission by surface elements, facet orientation distribution and facet density.

•Albedo depends on view angle

Answer: albedo plays the key role in surface energy balance as it decideshow much surface insolation is kept in Earth surface system

(1-α)Sd +LWd-εσTskin4 +SH+LE + G= 0

Why Is Surface Albedo Critical?

Surface Energy Budget:

This is a black spruce forest in the BOREAS experimental region in Canada. Left: backscattering (sun behind observer), note the bright region (hotspot) where all shadows are hidden. Right: forwardscattering (sun opposite observer), note the shadowed centers of trees and transmission of light through the edges of the canopies. Photograph by Don Deering.

http://www-modis.bu.edu/brdf/brdfexpl.html

A soybean field. Left: backscattering (sun behind observer). Right: forwardscattering (sun opposite observer), note the specular reflection of the leaves. Photograph by Don Deering. http://www-modis.bu.edu/brdf/brdfexpl.html

Wet and dry surfaces have different albedo

Boradband albedo

Spectral albedo – the reflectivity for specific wavelength

Albedo is function of wavelength.

Boradband albedo is the integrated value of spectral emissivity at all wavelength

An albedo value of 0.0 indicates that the surface absorbs all solar radiation, and a 1.0 albedo value represents total reflectivity.

http://theothermy.blogspot.com/2007/12/albedo-and-cool-roofs.html

0.0 0.2 0.4+No Data

CMG Broadband White-Sky Albedo (0.3-5.0m)14 - 29 September, 2001

No Data

CMG Broadband White-Sky Albedo (0.3-5.0m)1 - 16 January, 2002

0.0 0.2 0.4+

No Data

CMG Broadband White-Sky Albedo (0.3-5.0m)7 - 22 April, 2002

0.0 0.2 0.4+

Snow versus Non-snow Albedos 40–50°N Nov 00–Jan 01Snow versus Non-snow Albedos 40–50°N Nov 00–Jan 01

Jin et al., How does Snow Impact the Albedo of Vegetated Land Surfaces as Analyzed with MODIS Data?, in press, Geophys. Res. Let., 2002

Snow albedo is higher than non-snow albedo

Video: Snow Albedo Feedback

http://www.met.sjsu.edu/metr112-videos/MET%20112%20Video%20Library-MP4/energy%20balance-albedo/

Albedo-1.mp4

Energy of Earth

http://earthguide.ucsd.edu/earthguide/diagrams/energybalance/index.html

Useful link on energy balance:

Energy Balance video

http://www.met.sjsu.edu/metr112-videos/MET%20112%20Video%20Library-MP4/energy%20balance/

Earth’s Energy Budget.mp4

100% of the incoming energy from the sun is balanced by 100% percent total energy outgoing from the earth.

incoming energy from the Sun = outgoing energy from the Earth.

UnitsUnits

• Our class will use both English and Metric unit systems.• Most important:

– Distance (kilometres and miles) – Temperature (ºC and ºF)

• Conversions:

1.6 km = 1 mile; 1 km = 0.61 miles

(9/5 x ºC) + 32 = ºF

(ºF – 32) x 5/9 = ºC

Unit ReviewUnit Review

• What is the current temperature in ºC?

(current temp = 52F)• California is about 800 miles long (from

Oregon to Mexico). How many kilometers is that?

• If you were told that the average high temperature in Sydney Australia at this time of year is 26ºC, what temperature is that in ºF?

Class participation (2)

Three temperature scales:Three temperature scales:•KelvinKelvin•CelsiusCelsius•FahrenheitFahrenheit

•What does temperature What does temperature mean physically?mean physically?

•What does 0What does 0°° K mean? K mean?

°K= °C+273°K= °C+273

Temperaturethe degree of hotness or coldness of a body or environment (corresponding to its molecular activity)

Temperature is one of the principal parameters of thermodynamics. On the microscopic scale, temperature is defined as the average energy of microscopic motions of a single particle in the system per degree of freedom. On the macroscopic scale, temperature is the unique physical property that determines the direction of heat flow between two objects placed in thermal contact.

Cold temperature Warm temperature

Just an example, could be higher or lower

Energy Balance

• Assume that the Earth’s surface is in thermodynamic equilibrium:

• Thermodynamic Equilibrium: – The flow of energy

away the surface equals the flow of energy toward the surface

Surface

Average surface temperature = 15°C

http://en.wikipedia.org/wiki/Solar_radiation#Climate_effect_of_solar_radiation

since the Earth is much cooler than the Sun, its radiating energy is much weaker (long wavelength) infrared energy. energy radiation into the atmosphere as heat, rising from a hot road, creating shimmers on hot sunny days. The earth-atmosphere energy balance is achieved as the energy received from the Sun balances the energy lost by the Earth back into space. So, the Earth maintains a stable average temperature and therefore a stable climate.

http://www.srh.noaa.gov/jetstream//atmos/energy.htm

Group Discussion

If you go camping with friends. The first day and night are clear and the 2nd day and night are cloudy.

• Which day is cold?

• Which night is cold?

• Why?

The Transfer Of Heat: 3 ways

The heat source for our planet is the

Energy from the sun is transferred through space and through the earth's atmosphere to the earth's surface.

Since this energy warms the earth's surface and atmosphere,

some of it is or becomes heat energy.

There are three ways heat is transferred into and through the atmosphere:

radiation conductionconvection

sun

Radiation is the transfer of heat energy through space by electromagnetic radiation.

The flow of heat by conduction occurs via collisions between atoms and molecules in the substance and the subsequent transfer of kinetic energy.

Take a look: http://www.nationmaster.com/encyclopedia/Image:Translational-motion.gif

Fig. 2-2, p. 30

Convection is the transfer of heat energy in a fluid.

Cumulus clouds indicates where upward convection currents are

Other example: In kitchen liquid boiling