Transcript Ozone Hole
Ozone Hole • 1985, British scientists reported a sudden large depletion in the Ozone over the south pole • Simultaneous satellite measurements confirmed the decrease, but were rejected by the processing software-the decrease seen was so large it was rejected by the data quality control algorithms. • When the data were re-run through the processing programs without the data quality flags, the ozone hole had been seen all the way back to 1976! Causes • Unique set of conditions in the atmosphere at the south pole. • Polar Stratospheric Clouds (PSC) are clouds in the winter polar stratosphere at altitudes of 15,000–25,000 meters (50,000– 80,000 ft). • Due to their high altitude and the curvature of the surface of the Earth, these clouds will receive sunlight from below the horizon and reflect it to the ground, shining brightly well before dawn or after dusk. • PSCs form at very low temperatures, below −78 °C. PSCs and Ozone • Ordinarily, most of the chlorine in the stratosphere resides in stable "reservoir" compounds, primarily hydrochloric acid (HCl) and chlorine nitrate (ClONO2). • During the Antarctic winter and spring, reactions on the surface of the polar stratospheric cloud particles convert these "reservoir" compounds into reactive free radicals (Cl and ClO). • The clouds can also remove NO2 from the atmosphere by converting it to nitric acid, which prevents the newly formed ClO from being converted back into ClONO What is being done • 1976 Report by the National Academy of Science that there was credible scientific evidence for ozone depletion – US and several other countries banned the use of CFC in aerosol spray cans • 1985 Vienna Convention for the Protection of the Ozone Layer signed – Established a framework for the negotiation of international agreements regulating ozone depleting substances • 1987 Montreal Protocol is signed by 43 nations – Froze CFC production at 1986 levels and reduce it to 50% by 1999 – Follow up meeting in London modified it to to phase out CFCs entirely by 2000 – This date was moved up to 1996 in 1992 • CFCs replaced now by HCFCs or HFC (which are greenhouse gases) – Most commonly used in the US is HFC-134a (R-134a) which has replaced CFCs in automobile air conditioners Effect of these initiatives • Atmospheric concentrations have been declining • Antarctic Ozone hole will continue for decades • Expected to see Ozone concentrations increase by 5-10% in the lower stratosphere by 2020 • A return to pre 1980 levels is expected by 20602075. • Eventual complete recovery of the ozone will occur • Delays will be the result of developing countries which employ CFCs Global Warming • • The name given to the increase in the average temperature of the Earth’s near surface temperature and oceans that has occurred since the middle of the 20th century. In the graph to the right, panel a gives the Earth's surface temperature is shown year by year (red bars) and approximately decade by decade (black line, panel b gives 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. Greenhouse effect • Main culprit behind global warming • Sunlight enters the atmosphere and warms the Earth (UV, visible, IR) • At night, Earth radiates heat energy it gained during the day(mostly at IR wavelengths) • Not all of this energy escapes the atmosphere-some of it is absorbed and re-emitted back into the atmosphere, warming the atmosphere and the Earth. • Not necessarily a bad thingwithout it the Earth would be cold and life (a least as we know it) would not be possible Venus • Hottest planet in the solar system • But not the closest to the sun • Atmosphere is 96.5% carbon dioxide • Venus once had immense amounts of water, but no ozone layer-the UV radiation broke up the water molecules • Unfortunate, water absorbs carbon dioxide wand mitigates the greenhouse effect • Resulted in an extreme greenhouse effect Greenhouse effect-What could happen • Global temperatures rise until boiling point of water is reached • As water boils away, it becomes water vapor in the atmosphere, accelerating the heat rise (called positive feedback). • At a few hundred degrees celsius, carbon dioxide would be released from the rocks (sublimation), accelerating the heating again • Eventually the Earth would stabilize at surface temperatures similar to Venus (T=860F) • Worst case, not realistic scenario Greenhouse Gasses –in order of importance • • • • • • water vapor carbon dioxide methane nitrous oxide ozone CFCs Changes in greenhouse gas concentrations Gas Carbon dioxide Methane Nitrous oxide CFC-12 Preindustrial Level 280 ppm 700 ppb 270 ppb 0 Current Level 387ppm 1,745 ppb 314 ppb 533 ppt Increase since 1750 104 ppm 1,045 ppb 44 ppb 533 ppt • Historical variations can be tracked via analysis of ice cores – Ice core - a core sample (a cylindrical section of a naturally occurring medium consistent enough to hold a layered structure) from the accumulation of snow and ice over many years that have recrystallized and have trapped air bubbles from previous time periods. – The composition of these ice cores provides a picture of the climate at the time. – Record for over 800,000 years What do the ice cores tell us? • Natural variations occur in the greenhouse gas concentrations Post industrial revolution Man made sources of greenhouse gasses • Also called Anthropogenic, which designates an effect or object resulting from human activity • burning of fossil fuels and deforestation leading to higher carbon dioxide concentrations. – Account for one third of total anthropogenic CO2 emissions. • livestock enteric fermentation and manure management, paddy rice farming, land use and wetland changes, pipeline losses, and covered vented landfill emissions leading to higher methane atmospheric concentrations. Many of the newer style fully vented septic systems that enhance and target the fermentation process also are sources of atmospheric methane. • use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs and halons in fire suppression systems and manufacturing processes. • agricultural activities, including the use of fertilizers, that lead to higher nitrous oxide (N2O) concentrations. What are we seeing? • Since 1860-1900, global surface temperatures have increased by 1.35 F • Urban heat island effect only accounts for 0.02 C rise • Since 1979 land T have increased twice as fast as ocean temperatures • Temperatures on the lower troposphere have have increased by 0.62 between 1979 and 2000. Hold on, could it be the sun? • No overall increase in solar brightness in over 1000 years • Solar cycles do cause small variations in brightness, but not enough to account for what has been seen • No its not the sun Feedback-making the problem worse (or better) • Positive feedback-when the warming induces further warming • Negative feedback – when the warming induces a cooling