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Google Groups Help http://groups.google.com/group/met-10 Other available help Office hours 8:15 – 9:00 a.m. Monday/Wednesday Email at [email protected] Call me at (415) 205-2083 Meteorology department help on 6th floor Chapter 14: Climate Change The earth’s changing climate Possible causes of climatic change Global warming Why Climate Change Matters Why should you be aware of climate change? Climate is changing and your generation will be the one to make or break it Climate change (whether nature or manmade) will directly affect you! Determining Past Climates How do we know what past climates were like? Fossil evidence Fossils of tundra plants in New England suggest a colder climate Ocean sediment cores Certain animals must have lived in a range of ocean temperatures Oxygen isotope ratios Differing isotope counts mean differing temperatures Determining Past Climates How do we know what past climates were like? Ice cores Sulfuric acid in ice cores Oxygen isotopes (cold the air, the more isotopes) Bubbles in the ice contain trapped composition of the past atmospheres Dendrochronology Examining tree rings to see growth patterns Climate Through the Ages Much of Earth’s history was warmer than today by as much as 15°C Ice age Most recently 2.5 m.y.a. Beginning marked by glaciers in North America Interglacial periods (between glacial advances) When glaciers were at their max (18,000 – 22,000 years ago) sea level 395 feet lower than today This is when the sea bridge was exposed • 20,000 years ago the sea level was so low that the English Channel didn’t even exist. Climate Through the Ages Climate Through the Ages Temps began to rise 14,000 years ago Then temps sank again 12,700 years ago This is known as the Younger-Dryas Climate Through the Ages Temps rose again to about 5,000 years ago (Holocene Maximum). Good for plants Climate During the Past 1000 Years At 1000, Europe was relatively warm. Vineyards flourished and Vikings settled Iceland and Greenland Climate During the Past 1000 Years From 10001300 Huge famines due to large variations in weather. Crops suffered. Floods and great droughts Climate During the Past 1000 Years From 14001800 Slight cooling causes glaciers to expand Long winters, short summers. Vikings died Known as the Little Ice Age Climate During the Past 1000 Years Little Ice Age 1816 – “Year Without A summer” Very cold summer followed by extremely cold winter Temperature Trend During the Past 100-plus Years Warming from 1900 to 1945 Cooling to 1960, then increasing to today Temperature Trend During the Past 100-plus Years Sources of temperature readings Over land, over ocean, sea surface temps Warming in 20th century is 0.6°C Is global warming natural or manmade? External Causes of Climate Change How can we change the climate? Changes in incoming solar radiation Changes in the composition of the atmosphere Changes in the earth’s surface • Emissions of CO2 and other greenhouse gases are by no means the only way to change the climate. Climate Change and Feedback Mechanisms Water vapor-greenhouse feedback Explain it (is it positive or negative?) Runaway greenhouse effect Negative feedback mechanisms Increase in temp…increase in radiant energy to space What planet as a runaway greenhouse effect? Snow-albedo feedback (what kind is it?) Climate Change, Plate Tectonics, and Mountainbuilding Theory of plate tectonics – moving of plates like boats on a lake Evidence of plate tectonics Glacial features in Africa near sea level Fossils of tropical plants in high latitudes Climate Change, Plate Tectonics, and Mountainbuilding Landmasses at high latitude create glaciers Arrangements of landmasses disturb ocean currents Mountain building by plates running into each other Climate Change and Variations in the Earth’s Orbit Milankovitch theory As Earth moves around the sun, three different movements affect solar radiation Climate Change and Variations in the Earth’s Orbit Eccentricity Change in the shape of the orbit (from circular to elliptical Cycle is 100,000 years More elliptical, more variation in solar radiation Presently in Low eccentricity Climate Change and Variations in the Earth’s Orbit Obliquity Change in the tilt of Earth’s axis Cycle is 41,000 years Smaller the tilt, the less seasonal variation Axis tilts from 22° to 24.5° What is our current tilt Climate Change and Variations in the Earth’s Orbit Procession Wobble of the Earth as it spins The Earth wobbles like a top Currently, closest to the sun in January In 11,000 years, closest to the sun in July Climate Change and Variations in the Earth’s Orbit Climate Change and Atmospheric Particles Sulfate aerosols Put into the atmosphere by sulfur fossil fuels and volcanoes • Sulfate aerosols are thought to cool the climate and therefore counteract global warming to some extent. Climate Change and Atmospheric Particles Volcano aerosols May get into the stratosphere and absorb and reflect sunlight Thus, warms the stratosphere and cools the troposphere Climate Change and Atmospheric Particles Volcanic eruptions may be responsible for many of the climate’s cooling periods (Little Ice Age) Eruptions were larger 2.5 m.y.a and may be responsible for the Ice Age Climate Change and Variations in Solar Output Sunspots – magnetic storms on the sun that show up as dark region Maximum sunspots, maximum emission (11 years) Maunder minimum – 1645 to 1715 when few sunspots happened The Recent Warming Radiative forcing agents – greenhouse gases that can disturb the radiative equilibrium • Climate models are used to see the future • They use data from Carbon dioxide, other greenhouse gases, aerosols, and more Future Warming - Projections, Questions and Uncertainties Questions and uncertainties How fast will Carbon dioxide increase? Can we stop deforestation? Can we stop burning fossil fuels? Future Warming - Projections, Questions and Uncertainties Uncertain effect of clouds More clouds, more reflection to space? More clouds, more longwave radiation absorbed? Possible Consequences of Global Warming Projected temperatures Temperatures will rise most in high latitudes Expanding boreal forest will increase temps Plants and animals will die Precipitation will increase worldwide Possible effects on global circulation Weather shifts from normal pattern More rain than snow in the West Rise in sea level Melting glaciers Contamination of groundwater Possible Consequences of Global Warming Possible Consequences of Global Warming Fig. 14-20, p. 407 Global Warming and Human Impact on the Earth’s Surface Desertification – process of overgrazing and excessive cultivation of grasslands, causing desert conditions An interesting theory Plagues could be nature’s way of “curing” the Earth of Global Warming Plagues kills us and our effects, allowing the Earth to heal (Gaia Hypothesis) Curbing Global Warming Kyoto Protocol A format agreement by hundreds of nations to curb greenhouse emissions Try to reduce emissions by 5% below 1990 levels by 2012 Geoengineering Trying to fix the atmosphere with technology Idea to put sulfate aerosols into atmosphere to cool it