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UA GC 170A1 - Climate Change
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GC 170 1st Edition Lecture 14 Outline of Last Lecture I. Mid-Term ExamOutline of Current Lecture 1) Climate change over the past 1,000 years a. Medieval Warm Period b. Little Ice Age 2) Natural forcings on climate a. Sunspots b. Volcanoes Current LectureReview of past lectures- Enhanced Greenhouse effect explains global warmingo Rising CO2 levels and temperature correspondence o Global warming: Increasing temperature trend recorded since 1880- Definitions: o Climate change: Significant change in measures of climate (temp, precipitation) that lasts for an extended period of time o Global warming: Average increase in temperature in the atmosphere. It is only a PART of climate change (a big one).  Climate change that is related to human activities (fossil fuel emissions)o Greenhouse effect: Longwave radiation absorbed and remitted back to earth by the greenhouse gases (CO2, H2O, CH4, N2O) in the troposphere o Enhanced Greenhouse effect: Increased greenhouse gases from fossil fuel emissions have increased the amount of longwave radiated back to earth o Climate: Average of many year’s worth of weather for a location/region (average rainfall) o Climate Change: Long-term changes in the regional climate or earth’s average temperature occurring over decades to centuries o Climate variability: Short-term changes in the climate occurring over years to decades, usually related to natural climate forcings/influences- Instrumental recordso Weather stationso Weather balloonso Satellites These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Paleoclimate reconstructions: thousands of years are developed from proxy records (tree-rings, ice cores, pollen records)o Key to future: understanding past o Historical information provides a context for recent warming o Help us to predict the future environmental conditions- Climate over the past 1000 yearso Major warming over the past few decades  20th century warming is unpredictableo Small fluctuations in graph represent climate variabilityo Big climate changes that occur over centuries Medieval warm period- A period from 900 – 1300 AD- When average temperature in the northern Hemisphere was warmer (~ 0.5 degrees) than the 20th century- Evidence from Northern Europe (Vikings in Europe settled in Greenland for 400 years)- Western USo Arid and warmer across the western US o Several long and severe droughts lasting around 20 years inthe Southwesto Large communities of Native Americans dispersed (Hard tosustain large communities)- Medieval Period in Europe was a time of growth, many castles were built during the MWP Little Ice Age- Cool period from 1400 – 1800 AD- Glaciers more advanced in some places than they are today - Holland had a lot of continuous Ice- Periods of cooler temperatures, glacial advances and more freezing temperatures- Ice Ageso Large climate changes over thousands of years results in ice ages o Ice ages: related to changes in the earth’s orbit and the relationship between the earth and suno Holocene: Small climate change o Last ice age happened 15,000 to 20,000 years ago What causes Climate change & Climate variability without humans?- Sun Spotso Output of energy from the sun slightly varies over time  Changes amount of incoming solar radiation that reaches the earth’s surfaceo More sunspots means that the sun emits more solar radiationo Fewer sunspots during little ice age- Volcanic eruptions inject large amounts of ash into atmosphere o Blocks amount of incoming solar radiation reaching the earth surface and cools the climate. Explosive volcanic eruptions emit black ash & SO2 gas,  reaches the stratosphere SO2 converts to sulfate aerosols (Fine particles that reflect incoming solar radiation) remain in the stratosphere for 1 – 2 years (stratosphere is dry& sulfate aerosols are not rained out)o Cool the global climate for 1 – 2 yearso Volcanoes near equator cool more effectively Upper-level winds transport volcanic gases and ash to cover both hemispheres Higher latitudes winds transport the ash and gases to cover a smaller area (ex: only within the northern hemisphere)- Bristlecone pineso Cooler global temperatures for 1 – 2 years = narrow ringso Cold snaps for 1 – 2 weeks = Frost rings formThe current climate is a combination of HUMAN and NATURAL forcings: Fossil fuels, deforestationVolcanoes and


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UA GC 170A1 - Climate Change

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