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

Review Lecture 1 1.Two critical increases – global mean surface temperature and greenhouse gases 2. One key concept – greenhouse effect

Change in surface temperature in 20 th century

Two main points in this figure Global mean surface temperatures have increased °C since the late 19th century The 20th century's 10 warmest years all occurred in the last 15 years of the century Note: 1. why is global mean? 2. what is surface air temperature? (see next few slides)

The “Keeling curve,” a long-term record of atmospheric CO2 concentration measured at the Mauna Loa Observatory (Keeling et al.). Although the annual oscillations represent natural, seasonal variations, the long-term increase means that concentrations are higher than they have been in 400,000 years. Graphic courtesy of NASA’s Earth Observatory.

Methane

Greenhouse gases (important!) CO 2 CH 4 N 2 O (Nitrous Oxiode, so called “laughing gas”) CFC O 3 H 2 O by the early 21st century, N 2 O had become nearly as important a greenhouse gas as methane. Their best guess was 0.7°C for N 2 O, and 0.3°C for methane. Wang et al. (1976).Wang et al. (1976)

The Greenhouse Effect (Important concept)

Energy of Earth BALANCED

Useful link on energy balance:

Energy Balance Video videos/MET%20112%20Video%20Library- wmv/energy%20balance/ Earth’s Energy Budget.WMV

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

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 = 90F ) 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

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 Answer: statistical averaged speed of air molecules

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

Just an example, could be higher or lower

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.

All cell phones, once powered on, emit certain amounts of electromagnetic radiation in the microwave radio frequency range. eport that associated prolonged mobile phone use and exposure to differing amounts of cellular phone radiation to brain tumors, cancer, stress, headaches, cognitive problems, and sleep disorders

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

What forms you see here to transfer heat?

Albedo Definition The ratio of the outgoing solar radiation reflected by an object to the incoming solar radiation incident upon it. By Earth Observatory Glossary, NASA IN OUT I I α = I OUT I IN I IN : Incoming solar radiation reaching the object I out : Reflected solar radiaiton by the surface

Video Global Energy Balance - Albedo See video below to help your understanding a.Ice Albedo.wmv b.Clouds albedo.wmv -observe cloud and surface albedo, also observe shortwave radiation and lonwave radiation c. Globe Ice Albedo.wmv

Video Global Energy Balance What is the source of global energy? What is the difference between icesheet and ocean in terms of their reflections on incoming solar radiation?

Arctic sea ice coverage, 1979 and 2003, all students need to read NASA

Albedo Definition The ratio of the outgoing solar radiation reflected by an object to the incoming solar radiation incident upon it. By Earth Observatory Glossary, NASA IN OUT I I α = I OUT I IN I IN : Incoming solar radiation reaching the object I out : Reflected solar radiaiton by the surface

The Earth is not warming uniformly. 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 By Reading NASA we can see: (Important!)

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. This is why albedo 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 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.

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: Surface albedo

Albedo= 0.0 indicates that the surface absorbs all solar radiation, Albedo = 1.0 means that the surafce reflects all solar radiation

Albedo and Cool Roofs Cool roof needs High/Low albedo High/Low emissivity Handout: albedo and cool roofs

No Data NASA MODIS-Observed Albedo ( mm) For September, 2001

No Data NASA MODIS Observed Albedo For January, ( mm)

No Data NASA MODS-Observed Albedo For April, ( mm)

Conclusion from NASA MODIS Albedo (namely, the last few slides) Albedo varies across the global land surfaces. This is determined by land cover Albedo has clear seasonality Snow surafce has high albedo, forest has low albedo, desert has high albedo