METR112 Global Climate Change -- Lecture 2 Energy Balance and Prof. Menglin Jin San Jose State University Surface Albedo

The Land and Oceans have both warmed, but…

Video: Global Ice Albedo

Arctic sea ice coverage, 1979 and 2003 NASA

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 Glossary By NASA, Responsible NASA official: Dr. Michael D. King, IN OUT I 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,greenhouse effect can lower the albedo of the earth and cause global warming.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".Latin 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 decides how much surface insolation is kept in Earth surface system (1-α)S d +LW d -εσT skin 4 +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.

A soybean field. Left: backscattering (sun behind observer). Right: forwardscattering (sun opposite observer), note the specular reflection of the leaves. Photograph by Don Deering.

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.

No Data CMG Broadband White-Sky Albedo (  m) September, 2001

No Data CMG Broadband White-Sky Albedo (  m) January,

No Data CMG Broadband White-Sky Albedo (  m) April,

Surface reflectance is high at 2.2 µm, moderate at 0.66 µm, and low at 0.49 µm The aerosol effect on reflected solar radiation is small at 2.2 µm and large at 0.49 µm MODIS operational algorithm over land assumes Kaufman et al. (1997) A g (0.47 µm) = 0.5A g (0.66 µm) = 0.25A g (2.1 µm) Surface Reflectance at Near- Infrared Wavelengths

Snow 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 Albedo-1.mp4

Energy of Earth

Useful link on energy balance:

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.

Units 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 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: KelvinKelvin CelsiusCelsius FahrenheitFahrenheit What does temperature mean physically?What does temperature mean physically? What does 0° K mean?What does 0° K mean? °K= °C+273

Temperature the degree of hotness or coldness of a body or environment (corresponding to its molecular activity) Temperature is one of the principal parameters of thermodynamics.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.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

Temperature the degree of hotness or coldness of a body or environment (corresponding to its molecular activity) kelvin temperature scale (Abbreviated K; also called absolute temperature scale, thermodynamic temperature scale). An absolute temperature scale independent of the thermometric properties of the working substance. ( in which a change of 1 Kelvin equals a change of 1 degree Celsius; absolute zero - 0ºK is the lowest temperature on the Kelvin scale. The freezing point of water is +273ºK (Kelvin) and the boiling point of +373ºK ice point of pure water defined as K Temperature is one of the principal parameters of thermodynamics.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.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.

Just an example, could be higher or lower

Energy Balance Assume that the Earth’s surface is in thermodynamic equilibrium: Thermodynamic Equilibirum: –

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

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.

Group Discussion If you go camping with friends. The first day and night are clear and the 2 nd 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 conduction convection 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:

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