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Introduction to Global Warming and Climate Change APES/MOC/2007-2008 Factors That Affect Climate Changes • Ice core data shows that Earth’s temperature varies over time – Earth’s energy balance and albedo surfaces – Variation in insolation – Milankovitch cycles – Volcanoes, dust – Ocean currents – El Nino/La Nina cycles Earth’s Energy Balance Incoming solar radiation = energy reflected +energy absorbed Scientists from the National Aeronautics and Space Administration (NASA), The Earth Institute at Columbia University, and Lawrence Berkeley National Laboratory have confirmed that more energy is being absorbed from the Sun than is emitted back to space, throwing the Earth's energy "out of balance" and warming the planet. ( Using satellites, data from buoys and computer models . ) Albedo: a measure of how much solar energy is absorbed by a surface Reds and oranges show high albedo where the surface is very absorbing radiation, while blues and purples show surfaces that reflect more light. Insolation Varies • Normal variations in the sun’s radiation • Known from ice core data Q: Could reduced reflectivity, rather than greenhouse gases, explain the Earth's warming? A: Scientists have concluded: after monitoring the Earth's reflectivity for decades, changes in our planet's reflectivity can't explain the warming trend we currently are experiencing Milankovitch Cycles • Earth’s rotation and revolution combine to make the planet “wobble” in its orbit • This changes the position of the earth and affects seasonal temperatures and albedo • Such changes are believed to be principally responsible for the waxing and waning of glacial periods (100,000 yr. time spans) and normal climate cycles (20,000 – 40,000 year cycles) • Milankovitch cycles have tremendous value as a theory to explain ice-ages and long-term changes in the climate • they are unlikely to have very much impact on the decade-century timescale of global warming phenomenon • http://apollo.lsc.vsc.edu/classes/met130/note s/chapter16/graphics/71_Orbital_Fluctuations /A_71.swf Volcanoes and Dust • Volcanic dust blasted into the atmosphere causes temporary cooling. The amount of cooling depends on the amount of dust put into the air, and the duration of the cooling depends on the size of the dust particles • dust thrown up by windstorms or human activity can affect the passage of heat and light through the air ENSO • Climate “variability” are smaller-scale changes in the energy balance • Climate “change” may affect the intensity and frequency of ENSO events Ocean Currents Because freshwater is less dense than seawater, increased precipitation, melting of polar glaciers and ice caps could block the system by reducing the amount of cold water that sinks downwards. Models currently predict a 25% slow down of the Gulf Stream. There is no doubt that climate has natural variability over long periods of time HOWEVER: The most significant factor attributing to global warming and climate change at this time is believed to be the rising amount of greenhouse gases, such as carbon dioxide and methane, in the atmosphere... Greenhouse Effect: Natural Process that moderates our climate and makes life possible on earth. The Effect of Carbon Dioxide on Warming: The greenhouse effect refers to circumstances where the short wavelengths of visible light from the sun pass through the atmosphere and are absorbed by the earth’s surface. •The longer wavelengths of the infrared re-radiation from the heated surfaces are unable to pass through the atmosphere. •The trapping of the long wavelength radiation leads to more heating and a higher resultant temperature. •Carbon dioxide strongly absorbs infrared radiation, so the greater the carbon dioxide the more infrared absorption. •This leads to greater heat retention in the atmosphere. Human Impact on the Greenhouse Effect These are sketches of the graphs produced in the IPCC 2007 report of the increase in key greenhouse gases. They make clear that most of the increase of the last thousand years has occurred in the past 200 years. From 1980 to the end of the 21st century, temperatures are projected to increase by 1.8°C to 4.0°C. IPCC Conclusions • • • • Current warming trends are unequivocal. It is very likely that greenhouse gases released by human activities are responsible for most of the warming observed in the past fifty years. The warming is projected to continue and to increase over the course of the 21st century and beyond. Climate change already has a measurable impact on many natural and human systems: snow and ice are melting and frozen ground is thawing, hydrological and biological systems are changing and in some cases being disrupted, migrations are starting earlier, and species' geographic ranges are shifting towards the poles. Effects are projected to increase in the future and to be more severe with greater increases in temperature. Adaptation measures are already being implemented, and will be essential in order to address the projected consequences. There is, however, a limit to adaptation; mitigation measures will also be needed in order to reduce the severity of impacts. (NOTE: difficult to separate natural variability from climate change effects, more research needed). Mitigation measures that aim to reduce greenhouse gas emissions can help avoid, reduce or delay many impacts of climate change. Policy instruments could create incentives for producers and consumers to significantly invest in products, technologies and processes which emit less greenhouse gases. Without new mitigation policies, global greenhouse gas emissions will continue to grow over the coming decades and beyond. Rapid world-wide investments and deployment of mitigation technologies, as well as research into new energy sources will be necessary to achieve a stabilization of the concentration of greenhouse gases in the atmosphere. Additional research addressing gaps in knowledge would further reduce uncertainties and thus facilitate decision-making related to climate change. ADAPTATION and MITIGATION ADAPT: coastal defenses, government response to heat waves and flooding, technology solutions, modify consumption habits MITIGATE: reduce greenhouse gas emission • Kyoto (international cooperation); individual government policies to reduce emissions