MET 112 Global Climate Change - Lecture 2: Enegy Balance

Energy of Earth

Professor Menglin JinSan Jose State University, Department of Meteorology

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

Useful link on energy balance:

Average Earth surface temperature

Balance: IN OUT

Earth

At earth surfaceAt top of atmosphere

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

Greenhouse gases

Earth Surface

Simply put, greenhouse gases trap long-wave radiation and keep such energy in the Earth-atmosphere system, so that earth-atmosphere warms

Longwave radiation is emitted from surface.

Some surface radiation escapes to space

Most outgoing longwave is absorbed in atmosphere (by greenhouse gases)

Greenhouse gases emit longwave upward and downward

Some atmospheric radiation escapes to space

Some atmospheric radiation is absorbed at the surface

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

Removal of greenhouse gases would decrease downward flow of energy; now energy away from surface is greater than energy toward surface.

Sudden Removal of all Greenhouse Gases

Removal of greenhouse gases would decrease downward flow of energy; now energy away from surface is greater than energy toward surface.

Thus, average surface temperature starts to decrease.

Sudden Removal of all Greenhouse Gases

As surface cools, emission of radiation decreases until balance is restored. At this point, cooling stops

Sudden Removal of all Greenhouse Gases

As surface cools, emission of radiation decreases until balance is restored. At this point, cooling stops and equilibrium is restored.

Average surface temperature = -18°C

Result: A Very Cold Planet!

Question• Start with the following diagram and

assume the earth’s surface temperature is 15C and that the atmosphere has greenhouse gases.

• Imagine that the concentrations of greenhouse gases were to increase by 50%. 1. Draw two more diagrams illustrating (with arrows) how the energy balance would change with the increase in greenhouse gases and explain why.

• 2. How would the average surface temperature change? 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.

Details of Earth's energy balance (source: Kiehl and Trenberth, 1997). Numbers are in watts per square meter of Earth's surface, and some may be uncertain by as much as 20%. The greenhouse effect is associated with the absorption and reradiation of energy by atmospheric greenhouse gases and particles, resulting in a downward flux of infrared radiation from the atmosphere to the surface (back radiation) and therefore in a higher surface temperature. Note that the total rate at which energy leaves Earth(107 W/m2 of reflected sunlight plus 235 W/m2 of infrared] radiation) is equal to the 342 W/m2 of incident sunlight. Thus Earth is in approximate energy balance in this analysis.

The Transfer Of Heat

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

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. 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

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 was today’s low temperature in ºC?

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

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. (http://amsglossary.allenpress.com/glossary)

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 273.16K

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.

The size of the degree is the same as on the Celsius scale

SI unit of temperature is K

Absolute zero is where all kinetic motion in the particles comprising matter ceases and they are at complete rest in the “classic” (non-quantum mechanical) sense

the triple point of water is defined as being precisely 273.16 K and 0.01 °C.

In physics and chemistry, the triple point of a substance is the temperature and pressure at which three phases (gas, liquid, and solid) of that substance may coexist in thermodynamic equilibrium

Atmosphere Temperature is a measure of air molecules the kinetic energy of their move

temperature being an average energy per particle can only be defined at thermodynamic equilibrium, or at least local thermodynamic equilibrium (see below).

As a system receives heat, its temperature rises; similarly, a loss of heat from the system tends to decrease its temperature

When two systems are at the same temperature, no heat transfer occurs between them. When a temperature difference does exist, heat will tend to move from the higher-temperature system to the lower-temperature system, until they are at thermal equilibrium.

This heat transfer may occur via conduction, convection or radiation or combinations of them

The role of Temperature in nature

What is air temperature in this image?

the frost shown here is at -17 °C.

Many physical properties of materials including the phase (solid, liquid, gaseous or plasma), density, solubility, vapor pressure, and electrical conductivity depend on the temperature.

What weather conditions depend on air temperature?

Temperature also plays an important role in determining the rate and extent to which chemical reactions occur

MODIS daytime (10:30am) Tskin in October

Global surface temperature vary with location

(Jin and Dickinson 2008)

MODIS7 year averaged(2000-2007)

Improve Understanding of Tskin

July

January

Skin Temperature

May

July

seasonality

Diurnal Variation of Tskin

4. Evaluate NOAA GFS Tskin Simulation

Nighttime

Up to 5 degree higher in GFS than in MODIS along coast and high elevated area

GFS Tskin Oct 2007 (10:30 pm) MODIS Tskin Oct 2007 (10:30 pm)

Daytime

Higher Tskin in GFS than MODIS at the western part and mountain peaks

GFS Tskin Oct 2007 (10:30 am) MODIS Tskin Oct 2007 (10:30 am)

4. Evaluate NOAA GFS Tskin Simulation Using MODIS

Temperature controls many things, including the availability of water. In fact, a temperature increase of 5 to10 °F (3 to 6 °C) in the United States could result in a decrease in soil moisture of 10 to 30 percent during the summer. A decrease in soil moisture could cause natural vegetation and crops to dry out. This could severely impact the environment as well as the economy

Temperature and Water

Atmospheric carbon dioxide concentration(ppmv) and temperature change (°C) observed during the past 160 thousand years and predicted during the next 10 thousand years. Historical carbon dioxide data was collected from Antarctic ice cores; temperature changes through time are relative to the present temperature. Graph adapted from the Whitehouse Initiative on Global Climate Change. 

As concentrations of CO2 in the air decrease, so does the temperature.

As concentrations of CO2 in the air increase, so does the temperature.

Concentrations of atmospheric CO2 are expected to increase dramatically in the future. Even if emissions of CO2 stay the same as they are now, concentrations of atmospheric CO2 will increase to 700 ppm by 2100 (see Remote Sensing: Carbon Dioxide. As a result, mean global temperatures will increase by 3.5 °F (1.9 °C) over the next 100 years. 

CO2 vs Temperature