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MET 112 Global Climate Change - Lecture 2: Energy Balance
Energy of Earth
Professor Menglin JinSan Jose State University, Department of Meteorology
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
Class Participation
What is today’s minimum temperature? How much is it in °C ?
99°F | 61°F
Thursday
http://earthguide.ucsd.edu/earthguide/diagrams/energybalance/index.html
Useful link on energy balance:
Average Earth surface temperature
Anthropogenic Methane Sources
• Leakage from natural gas pipelines and coal mines
• Emissions from cattle
• Emissions from rice paddies
Methane (CH4) is produced by anaerobic decay of organic material in landfills, wetlands, and rice fields; enteric fermentation in the digestive tracts of ruminant animals such as cattle, goats, and sheep; manure management; wastewater treatment; fossil fuel combustion; and leaks from natural gas transportation and distribution systems and abandoned coal mines.
anaerobicDescribes an organism that is able to live without oxygen. Also used to describe environments that are devoid of gaseous or dissolved molecular oxygen.
Question from last class: Why rice paddies produce Methane?
http://www.learner.org/channel/courses/envsci/unit/text.php?unit=2&secNum=4
http://en.wikipedia.org/wiki/Solar_radiation#Climate_effect_of_solar_radiation
Importance of human-produced greenhouse gases
Source: Courtesy Marian Koshland Science Museum of the National Academy of Sciences http://www.koshland-science-museum.org.
Balance: IN OUT
Earth
At earth surfaceAt top of atmosphere
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
Class Participation
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
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
Absolute zero (see next page)
Temperature Definition
•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.
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)
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
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 size of the degree is the same as on the Celsius scale
SI unit of temperature is K
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 Surface Temperature
July
January
Sea Breeze: determined by air-surface temperatures
Source: Adapted from graphic by National Oceanic Atmospheric Administration, Jet Stream.
Example of Importance of surface temperature
Skin Temperature
May
July
seasonality
Diurnal Variation of Surface Temperature
NASA EOS MODIS Observed Surface Temperature
NighttimeMODIS 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
Source: Vimeux, F., K.M. Cuffey, and Jouzel, J., 2002, "New insights into Southern Hemispheretemperature changes from Vostok ice cores using deuterium excess correction", Earth and PlanetaryScience Letters, 203, 829-843.
CO2, CH4 and temperature records from Antarctic ice core data