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Fundamentals • • • • • • • • • Atmosphere Climate Variation Greenhouse Effect Climate Drivers Carbon Cycle Energy Balance System Inertia Geologic time Causes of Climate Change Earth’s Atmospheric Composition, Temperatures and Pressure Composition Percent Nitrogen (N2) 78 Oxygen (O2) 21 Argon (Ar) Carbon Dioxide (CO2) Water Vapor (H2O) Sea level Surface Pressure (Bars) Extreme Surface Temperatures (°C) 0.93 0.038 0-4 1 60 to −130 (Global Mean = 14.6) Atmospheric Abundance of CO2 and Global Temperatures CO2 Percent Average Global Temperature (°C) 0.018 9 Last Ice Age Maximum 0.028 13 Interglacial Period (Holocene) 0.038 14.6 0.045 16 Critical for Humans and Other Species 0.065 18 Catastrophic for Humans and Other Species ~0.15 25 Hot House Maximum 96.5 480 Venus Surface Event Today Climate Shift and Temperature Natural Variations of Climate during Warming One Way of Causing Short-term Climate Variations The Greenhouse Effect changes in the global average temperature result in Small large climate changes • A 5° C drop in the global average temperature places us in the depths of an Ice Age. • An 8° C rise in the global average temperature places us near the top of a Hot House. Greenhouse Gases and Percent Warming • Carbon Dioxide - CO2 (56%) • Methane - CH4 (16%) • Tropospheric Ozone - O3 (12%) • Halocarbons (11%) • Nitrous Oxide - N2O (5%) Climate Drivers Change in Temperature with Height for 2 Amounts of CO2 Continental Absorption of CO2 Energy Balance of the Earth INERTIA • General Physics…the resistance to change in some physical property of a body or system. • Global Warming…the resistance to change in direction of various elements of the climate system, such as rising atmospheric CO2, rising temperatures and melting ice. Inertia in Action • CFCs have decreased dramatically during the past 20 years. • The ozone hole in 2006 was as large as ever because of the long lifetime of CFCs in the stratosphere and continuing emissions. • It will take about 70 years for the ozone hole to disappear. Other Climate Basics • Feedbacks can cause the climate to move in one direction or the other independent of the original cause. • Abrupt climate changes can drive the climate very rapidly; up to 8° C in 10 years or less. • Uncertainties Geologic Time and Natural Causes of Climate Change Geologic Timescale Red and blue areas indicate hot (Hot House) and cold (Ice House) periods The Geologic Time Scale Relative to One Year Absolute Time Eon or Era Duration Percent (million years) Geologic time Relative to a year Starting time Duration Precambrian 3,996 88.0 January 1 10 mo. 17 d Paleozoic 296 6.5 November 18 24 days Mesozoic 183 4.1 December 12 15 days Cenozoic 65 1.4 December 26 5 days Major Human Events Relative to One Year December 31 Years before present Starting time Duration* Human development begins ~7 million 10:30 a.m. 13 hr., 30 min. Homo species begins 2.3 million 7:34 p.m. 4 hr., 26 min. Early Homo Sapiens 400,000 11:14 p.m. 46 min. Homo Sapiens Sapiens (us) 125,000 11:46 p.m. 14 min. 12,000 11:58:21 p.m. 1 min., 21 sec. Bonze Age begins 5000 11:59:34 p.m. 35 sec. Early writing 4000 11:59:32 p.m. 28 sec. 250 11:59:58.3 p.m. 1.7 sec. Average human lifetime 75 11:59:59.4 p.m. 0.6 sec. Current rapid climate warming 25 11:59:59.9 p.m. 0.1 sec. Major Event Civilization begins (Agriculture) Industrial Revolution (technology) *Starting time to the present. The Anthopocene Epoch • The Anthopocene is a new Epoch characterized by human-caused major global changes that have altered the Earth in fundamental ways. • It starts near the beginning of the Industrial Revolution in 1751. • We are no longer in the Holocene. Some Major Changes to Earth by Humans • • • • Changed Carbon Cycle Climate Change Ocean Acidification Urbanization and Habitat Encroachment • Deforestation • Major Depletion of Marine Food Fish • Major Disruption of Land Surfaces Beginning of the Anthropocene • The diagram shows some of the criteria that defines the Anthropocene. • The effects of these changes will leave a distinct stratigraphic marker. Mass Extinctions • The K/T extinction was probably due to a large impact that radically changed the climate. • The other extinctions appear to be due to natural climate changes. • The greatest mass extinction (P/T) was due to a climate change from an Ice House to a Hot House. Causes of Climate Change • Abundance of Greenhouse Gases • Major Volcanic Eruptions • Large Asteroid or Comet Impact • Change in Sun’s Irradiance • Change in Ocean Circulation • Continental Drift • Change in Earth’s Motions Red = main cause of current global warming Past Oxygen and CO2 Abundances Major Volcanic Eruptions • Large volcanic eruptions can cool the climate for a few years by injecting ash into the stratosphere to reflect the Sun’s radiation back to space. • Enormous eruptions over long periods can emit large amounts of CO2 to warm the climate. Mt. Pinatubo eruption lowered the global average temperature between 0.2 and 0.6° C from mid-June 1991 and about 1995 Large Asteroid or Comet Impacts • Large impacts cool the climate by injecting dust into the stratosphere to reflect sunlight back to space. • If the impact is in limestone a large impact will first cool the climate and then heat it up by releasing large amount of CO2 from the limestone. Changes in the Ocean’s Thermohaline Circulation Can Change the Climate Continental Drift due to Plate Tectonics can Change Climate over Millions of Years Changes in Earth’s Motions can Change the Climate Variations in the Earth’s Insolation with Time Changes in the Sun’s Irradiance Soar irradiance through September 2008. Reference: Fröhlich, C. and J. Lean, Astron. Astrophys. Rev., 12, pp. 273--320, 2004. http://www.pmodwrc.ch/pmod.php?topic=tsi/composite/SolarConstant Solar Irradiance Does Not Correlate with Human-caused Temperature Increase Measurements of Surface Temperature and Sun’s Energy Solar Irradiance, Temperature, and Atmospheric CO2 Solar Irradiance, Temperature, and Human-Caused CO2 Emissions Conclusions • Only two causes can operate on time scales short enough to account for today’s rapid warming: 1) increase in solar irradiance, or 2) increase in greenhouse gases. • The increase in solar irradiance is not enough to account for the present warming, and does not correlate with its rapid rise. • The increase in greenhouse gases must be the primary cause of global warming. • This is consistent with the observed rapid rise in both greenhouse gases and their emission by human activities.