Global Climate Change Dr Craig Clements San Jos State University MET 10 Global Climate Change Chapter 14 Review Why is CO2 So Important Carbon Dioxide is a greenhouse gas Greenhouse gases are those gases that cause the greenhouse effect The greenhouse effect makes a planet s surface temperature warmer than it would otherwise be The stronger the greenhouse effect the warmer the surface other factors being equal Consider the blanket analogy Earth s Energy Balance Energy entering top of atmosphere Energy leaving top of atmospher Energy entering the Earth s surface Energy leaving Earth s surface Conservation of Energy Absorption of Radiation in the Earth s Atmosphere Incoming solar radiation Each beam of incoming sunlight can be either Reflected back to space Albedo Clouds Atmosphere Surface Or absorbed either by atmosphere e g clouds or ozone or Earth s surface Some surface radiation escapes to space Most outgoing longwave is absorbed in atmospher e by greenhou se gases Longwave radiation is emitted from surface Some atmospheric radiation escapes to space Greenhous e gases emit longwave upward and downward Some atmospheric radiation is absorbed at the surface Greenhouse Effect Sequence of steps 1 Solar radiation absorbed by earth s surface 2 Earth gives off infrared radiation 3 Greenhouse gases absorb some of the Earth s infrared radiation 4 Greenhouse gases water and CO2 give off infrared radiation in all directions 5 Earth absorbs downward directed infrared radiation Result warmer surface temperature 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 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 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 Result A Very Cold Planet 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 Earth s Greenhouse Effect Without the greenhouse effect the surface temperature of Earth would be Way Cold 18 C Greenhouse gases play an important role in shaping climate More GHGs warmer climate Less GHGs cooler climate Recent Climate Change Modeled temperature changes IPCC 2007 b Additionally the year by year blue curve and 50 year average black curve variations of the average surface temperature of the Northern Hemisphere for the past 1000 years have been reconstructed from proxy data calibrated against thermometer data see list of the main proxy data in the diagram The 95 confidence range in the annual data is represented by the grey region These uncertainties increase in more distant times and are always much larger than in the instrumental record due to the use of relatively sparse proxy data Nevertheless the rate and duration of warming of the 20th century has been much greater than in any of the previous nine centuries Similarly it is likely7 that the 1990s have been the warmest decade and 1998 the warmest year of the millennium Latest global temperatures Over the last 140 years the best estimate is that the global average surface temperature has increased by 0 6 0 2 C IPCC 2001 So the temperature trend is 0 6 C 0 2 C What does this mean Temperature trend is between 0 8 C and 0 4 C The Uncertainty 0 2 C is critical component to the observed trend CO2 Concentration in Atmosphere Short Term Carbon Cycle One example of the short term carbon cycle involves plants Photosynthesis is the conversion of carbon dioxide and water into a sugar called glucose carbohydrate using sunlight energy Oxygen is produced as a waste product Plants require Sunlight water and carbon from CO2 in atmosphere or ocean to produce carbohydrates food to grow When plants decay carbon is mostly returned to the atmosphere respiration During spring more photosynthesis atmospheric CO2 levels go down slightly During fall more respiration atmospheric CO2 levels go up slightly Current CO2 387 ppm What Changed Around 1800 Industrial Revolution Increased burning of fossil fuels Also extensive changes in land use began the clearing and removal of forests Burning of Fossil Fuels Fossil Fuels Fuels obtained from the earth are part of the buried organic carbon reservoir Examples Coal petroleum products natural gas The burning of fossil fuels is essentially A large acceleration of the oxidation of buried organic carbon Land Use Changes Deforestation The intentional clearing of forests for farmland and habitation This process is essentially an acceleration of one part of the short term carbon cycle the decay of dead vegetation Also causes change in surface albedo generally cooling Climate Feedbacks Earth s Climate The Earth s climate is fairly stable in terms of temperature This can be visualized using in the following system diagram The idea is that even though the system may change away from it s initial point it will have the tendency to go back to normal eventually 2 3 1 Stable Stable Stability versus instability Stable Given a perturbation the system tends to return to original state Instability Given a perturbation the system moves to another state Stable equilibrium Unstable equilibrium States of equilibrium The system may have multiple states of equilibrium 2 3 1 Stable to small perturbations until a big force perturbs the system into a new equilibrium Climate Stability The Earth s climate changes as a result of internal external forcing Changes in solar radiation Changes in the earth s orbit Plate tectonics Volcanoes Human pollution etc These forcings can be thought of as a perturbation or push to climate stability These changes can be enhanced or diminished by positive or negative feedbacks Climate Stability Internal Forcing mechanisms processes that are internal to the climate system that involve the various elements ice water vapor CO2 External Forcing mechanisms some forcing that can alter the system without itself being altered solar variability axis wobble etc Climate