Solar Radiation• The Sun, with a surface temperature of nearly 6,000 degrees K, emits radiation in the ultra- violet(8%), visible(43%) and infra-red (49%) regions of the electro-magnetic spectrum.• The Earth intercepts about 0.5 billionth of the Sun’s total radiation• About half of the solar radiation reaching the lower atmosphere actually warms the Earth’s surface (15 degrees C average).• The remainder of the radiation is either reflected by clouds and oceans, or absorbed by gases in the atmosphere.
Solar Radiation• The solar constant is defined as the amount of solar energy per second that falls on an area of 1m2 of the upper atmosphere perpendicular to the suns’ rays• Another name for the solar constant is the sun’s energy flux• The solar constant has a value of 1.35 kWm-2• The solar constant varies due to the elliptical orbit of the Earth and age of Sun.• The total solar radiation reaching the top of the atmosphere is about 1.7 x 10 17 W which is 170 Wm-2 averaged over a day and night
Solar Radiation• The total solar radiation is 170 Wm-2 averaged over a day and night how much energy does 1km2 of the Earth receive in a day?
Albedo• Albedo at a surface is the ratio between the incoming radiation and the amount reflected …expressed as a % or coefficient• Albedo = reflected into space % incoming radiation• Recall solar radiation is mainly in the visible and infrared regions (we call the incoming short wave infrared insolation)
Variations in albedoSample albedos Surface Typical Albedo The albedo also varies withFresh asphalt 0.04 factors like season, latitudeConifer forest 0.08,0.09 to 0.15 and cloud cover(Summer)Worn asphalt 0.12Deciduous trees 0.15 to 0.18 The average value on EarthBare soil 0.17 is 0.3Green grass 0.25Desert sand 0.40New concrete 0.55Fresh snow 0.80–0.90
• Greenhouse gases absorb infra-red radiation strongly in the bands with wavelengths between 12,500 – 17,000 nm and 4,500 – 7,000 nm. In between these two bands more than 70% of the radiation is emitted from the Earth’s surface escapes through the atmosphere.• When infra-red radiation is absorbed the bonds in the molecules to vibrate, where the distances between bonded atoms increases and decreases in a rhythmical manner as if connected by springs.• It is possible for resonance to occur if the vibration frequency matches the molecules natural frequency (for greenhouse gases their natural f is in the infrared region)
IR absorption of greenhouse gases• Polyatomic molecules have more numerous vibrations, at least some of which are ‘infrared- active’. The main infrared absorbers in the atmosphere are water and carbon dioxide. At the long wavelengths of terrestrials radiation, the bending vibrations of these molecules are chiefly responsible for absorption.
AlbedoIncoming radiation will be INSOLATED, REFLECTED and RETRANSMITTED in various ways.• 30% reflected• 51% absorbed at surface(23% of which is used in the water cycle)• 19% absorbed in atmosphereAlbedo is affected by seasons, day, latitude.Global annual mean albedo is 0.3
What is the Greenhouse Effect? The greenhouse effect is a natural warming process. Put simply natural greenhouse gases absorb outgoing long wave radiation and re-radiate some of it back to Earth• The absorbed energy warms the earths surface which then emits heat energy back toward space as longwave (infra-red) radiation. This outgoing infra-red radiation is partially absorbed by greenhouse gases which then radiate the energy in all directions, warming the earths surface and lower atmosphere.• Without these greenhouse gases the earths average surface temperature would be about 33 degrees Celsius cooler, that is the same temperature as the Moon.
Greenhouse Gases• The main natural greenhouse gases are water vapour, carbon dioxide, methane, and nitrous oxide.• All except water vapour have increased in concentrations in the atmosphere since the 1950s.• Other greenhouse gases include ozone and halocarbons.• Most of the greenhouse effect is due to water, with carbon dioxide contributing about 1 degree to the warming effect.• Only polar molecules can absorb infra-red radiation so the most common gases in the atmosphere, oxygen (O2) and nitrogen (N2), do not contribute to the Greenhouse Effect.
Source of GasesGreenhouse Main Human ActivityGas SourceCarbon Combustion of Transport, power and fossil fuels energy production,dioxide burning of rainforests.Methane Anaerobic Rice growing, cattle and breakdown of sheep farming plant matterNitrous Oxide Denitrification Use of nitrogenous of nitrates by fertilizers in microbes agriculture
Black body radiation• A black body is an object that absorbs all electromagnetic radiation that falls on it. No electromagnetic radiation passes through it and none is reflected. Because no light (visible electromagnetic radiation) is reflected or transmitted, the object appears black when it is cold. If the black body is hot, these properties make it an ideal source of thermal radiation.• From the measured values for the Sun, Ts=5778K Rs=6.96 * 108m D=1.496*1011 albedo=0.367 well find the effective temperature of the Earth to be Te=248.53K This is the black body temperature that would cause the same amount of energy emission, as measured from space, while the surface temperature is higher due to the greenhouse effect.
Black body radiation• Graph of light emission at different Temperatures
Black body radiation• Stefan BoltzmannThe energy radiated by a blackbody radiator per second per unit area is proportional to the fourth power of the absolute temperature and is given by
Emissivity• The Earth is not a perfect Black Body radiator• The emissivity is defined as power − radiated − by − object Power − from − black − body − at − same − tempTherefore the Earth is not a perfect absorber or emitter ofheat. Black objects have a high emissivity, white low.
Values of emissivityAluminium: anodised 0.77Aluminium: polished 0.05Asbestos: board 0.96Asbestos: fabric 0.78Asbestos: paper 0.93Asbestos: slate 0.96Brass: highly polished 0.03Brass: oxidized 0.61Brick: common .81-.86Brick: common, red 0.93Brick: facing, red 0.92Brick: fireclay 0.75Brick: masonry 0.94Brick: red 0.90Carbon: candle soot 0.95Carbon: graphite, filed surface 0.98
Surface heat capacityAlso known simply as specific heat, is the measure of the heat energy required to increase the temperature of a unit quantity of a substance by a certain temperature interval.More heat energy is required to increase the temperature of a substance with high specific heat capacity than one with low specific heat capacity.Molecules have internal structure because they are composed of atoms that have different ways of moving within molecules. Kinetic energy stored in these internal degrees of freedom contributes to a substance’s specific heat capacity and not to its temperature.
Surface Heat capacity CsSurface heat capacity is the energy required to raisethe temperature of unit area of a planet’s surface byone degree, and is measured inJ m–2 K–1.
Climate change modelStudents should appreciate that the change of aplanet’s temperature over a period of time is givenby:(incoming radiation intensity – outgoing radiationintensity) × time / surface heat capacity.
Energy balance modelsThere are four main categories of model:• EBM – use spreadsheets to study incoming/outgoing global radiation, using different latitudes from equator to pole• RCM – simulate atmospheric environments, only radiation balance and convection heat transfer• STM – combination of energy balance and radiative-convective models• GCM – 3D general circulation model simulating global climate
Global Warming?• The natural greenhouse effect has been significantly intensified by human activities that increase the concentrations of greenhouse gases (mostly carbon dioxide, methane and nitrous oxide) in the atmosphere.• These greenhouse gases increase the retention of heat in the troposphere and contribute toward (cause) global warming or, more accurately, climate change. (Note: Not all parts of the Earth may experience increases in temperatures e.g. UK temperatures may decrease.)
Global WarmingChange in composition of greenhouse gasesIncreased solar flare activityCyclical change in Earths orbitVolcanic activityContinental drift affecting ocean currentsWhich is responsible???
Enhanced greenhouse effect• Among the most significant causes of increased concentration of greenhouse gases are power generation using fossil fuels and the destruction of forests.• Global temperatures have been increasing dramatically throughout the 20th century and, according to the Australian Greenhouse Office publication Climate Change: An Australian Guide to the Science and P : "the 1990s were the warmest decade and 1998 the warmest year of the millennium".• In the past 50 years, for example, South Australias average temperature has risen by 0.84°C and the CSIRO projects that it will rise between 1° to 6°C by 2070.
Major Impacts• A Rise in Temperature varying with latitude & season, with longer summers and shorter winters.• Change in Climate with small temperature changes resulting in large impacts on climate.• Higher Evaporation Rates and increased, but uneven, global rainfall (drier South Australia, wetter Northern Territory).• Change in Natural Ecosystems with increasing extinction of native flora and fauna.• Increase in Photosynthesis with domination of weed species.• Rises in Sea Level due to warming and expansion of oceans and melting of land-based ice.• Weather Extremes during the transition to an enhanced greenhouse Earth.
Major ImpactsWhat evidence do we have for global warming?• Ice core data• Tree ring data• Sedimentary records• Glacial melting
Coefficient of Volume Expansion.Basically what it is, is the measurement of the change in volume per degree change in temperature. It measures volume change with respect to temperature change. ∆V is the change in volume, V0 is the original volume (initial volume) and ∆T is the change in temperature.
Coefficient of Volume Expansion.If heat increases the volume increases, if the volume increase the heat must increase as well.Applicable to all materials as every different material expands and contracts with temperature change, but just to different degrees of expansion and contraction.
Coefficient of Volume Expansion.eg. Railway lines buckling due to heat, an air balloon being shrunk and expanding with the change in temperature, heat switches which switch on and off at This is a useful measurement as we can then predict the rise and fall of the water levels due to the increase of heat or the decrease of heat.
Mechanisms for global warming• Rise in mean sea level• Change in temp• Change in snow/ice• Change in earth vegetation – deforestation• Gridlock cities – more pollution• Use of non-renewable energy
IPCC• The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body formed to evaluate the risk of climate change caused by human activity.• Established in 1988• Does not carry out research• Instead publishes reports relevant to the UN Framework Convention on Climate Change• Reports based on scientific evidence and is a reflection of viewpoints within the scientific community• Working group 1 deals with "The Physical Science Basis of Climate Change"• Working group 2 deals with "Climate Change Impact, Adaptation and Vulnerability"• Working Group 3 deals with "Mitigation of Climate Change"• There is also the Taskforce on National Greenhouse Gas Inventories, which is tasked with developing a method of measuring GHG emissions
Kyoto Protocol• major international agreement regarding environmental damage• intended to achieve "stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system"• signed and ratified by most nations - all the worlds powers, with the exception of the USA• suggests "common but differentiated responsibility" – developing countries exempt from emission targets – despite this, it is still the responsibility of developing countries to reduce emissions• implements emissions trading by which countries with emissions below the target can gain financially, and countries who exceed the limit are punished
• The targets cover emissions of the six main greenhouse gases: – Carbon dioxide (CO2) – Methane (CH4) – Nitrous oxide (N2O) – Hydrofluorocarbons (HFCs) – Perfluorocarbons (PFCs) – Sulphur hexafluoride (SF6)
• Under Kyoto, industrialized countries agreed to reduce their collective GHG emissions by 5.2% compared to the year 1990 – Highest National target reduction: 8% for EU – Calls for no change in Russian emissions – The treaty permitted an increase in greenhouse emissions of 8% for Australia and 10% for Iceland to permit further industrialisation for those countries
APPCDC• Asia-Pacific Partnership on Clean Development and ClimateMembers:• Australia• Canada• China• India• Japan• South Korea• USAUnlike the Kyoto Protocol, the APPCDC does not impose mandatory emissions reductions, it allows member country to set their own targets. This has been criticised as worthless, but unlike Kyoto protocol, it attempts to have China and India reduce their emissions.
Further InformationThe Australian Greenhouse Office website includes two excellent resources for learning more about Climate Change.• The following frequently asked questions provide introductory information. http://www.greenhouse.gov.au/science/faq/index.html• Climate Change: An Australian Guide to the Science and Potential Impact, a new CSIRO publication details global and Australian climate change science. Youll find it on the Australian Greenhouse Office website at http://www.greenhouse.gov.au/science/guide/• The British Broadcasting Commission (BBC) has an excellent Guide to Climate Change, complete with graphics and accessible explanations at http://news.bbc.co.uk/1/shared/spl/hi/sci_nat/04/climate_change/html/climate.s . However, there is an inevitable UK/European emphasis