GC 170 1st Edition Lecture 14 Outline of Last Lecture I Mid Term Exam Outline 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 Lecture Review of past lectures Enhanced Greenhouse effect explains global warming o 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 records o Weather stations o Weather balloons o 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 years o Major warming over the past few decades 20th century warming is unpredictable o Small fluctuations in graph represent climate variability o 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 US o Arid and warmer across the western US o Several long and severe droughts lasting around 20 years in the Southwest o Large communities of Native Americans dispersed Hard to sustain 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 Ages o 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 sun o 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 Spots o Output of energy from the sun slightly varies over time Changes amount of incoming solar radiation that reaches the earth s surface o More sunspots means that the sun emits more solar radiation o 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 years o 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 pines o Cooler global temperatures for 1 2 years narrow rings o Cold snaps for 1 2 weeks Frost rings form The current climate is a combination of HUMAN and NATURAL forcings Fossil fuels deforestation Volcanoes and sunspots