ATMO 336 1st Edition Lecture 27 Outline of Last Lecture II. Climate model forecastsIII. Predictions of equilibrium temperature after doubling CO2IV. Model predictions of temperature changes for the 21st centuryI. Climate model predictions for extreme weather events Outline of Current Lecture V. Were climates of earth always as they were today?VI. Why do we need to understand the climates of the pastVII. How do we know what climate was like in the pasta. Proxy recordsb. Environmental indicatorsVIII. Before the PleistoceneIX. The Pleistocenea. The pastb. Connection to present day climatec. Important points from the PleistoceneX. Slight variations in the earths orbital parametes have resulted in significant climate changea. Paleoclimate perspectiveb. Cycles in earths orbital parametersi. Eccentricityii. Obliquityiii. Precessionc. Milutin milankovich and his discoverysCurrent Lecture- Where climates of earth always as they were today?o Enough evidence in historic geologic records that say noo Glaciers cover 10% of earths surface today If temps were to rise enough and this ice would melt, level of ocean would rise 65m (213ft)- Why do we need to understand the climates of the pasto Give us idea about magnitude and speed of natural climate changes throughout earths historyo Help us understand present day climate and how it might change in the futureo Test hypotheses about the causes of climate changeThese 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.- How do we know what climate was like in the pasto Proxy records= inferred records of past climate that are not based on direct measurements. Include archeological information about past human civilizations , written accounts, and environmental indicators = decent reconstructions of medieval times and back a few thousand yearso wide range of scientific techniques can be applied to different kinds of environmental evidence to provide a picture of climatic variation. Na few of these are: (environmental indicators) plant and animal residues ( fossil records) glacier fluctuations (advance and retreat of glaciers) fluctuations in lake levels dedroclimatology (tree rings) oxygen isotope data ice cores ocean/lake sediment cores- before the Pleistoceneo global climate much warmer than now (8-15 degrees C warmer)o polar regions free of iceo interrupted with glacial period about 700million years ago - the Pleistoceneo most recent glacial period (2 million years before present)o not a period of continuous glaciation but a time when glaciers alternately advanced and retreated over large portions of North America and Europeo most important environmental event since the human species has been on earth (oscillation between glaciation and interglacial periods)o at least 20 glacial/interglacial cycles during the Pleistoceneo glaciers can extend as far south as the northern parts of US, but do not reach into the tropics (tropics still warm during ice age)o sea level fluctuated almost continuously between interglacial levels Bering shelf exposed at the time of the last glaciation 9siberia connected to Alaska by a land bridge where early humans walked across)o today, we are in a interglacial period where sea level is more than 100 meters higher than it was during the glacial period (land bridge now covered)o in areas of earth not covered by glaciers, climate differences during ice age cycles include: many inland areas had much wetter climates evidence of large inland lakes in present basin areas (great basin in US and parts of Africa) shifts in rainfall belts; reduced evaporation and increased cloudinesso Pleistocene reached max 22,000-14,000 yBP Two large ice sheets in northern hemisphere (laurentide icea sheet in eastern North America, Scandinavian ice sheet in Northern Europe) Max areas of northern hemisphere ice sheets= 90% Sea level dropped by 85 meters and sea surface temp fell by 10 degrees C in mid latitudes, 3 degrees C in Caribbean.o Evidence suggests that temperature causes carbon dioxide and methane concentrations to change ( not the other way around) This was discovered by using more precise tech. in ice cores It was found that changes in the greenhouse gases carbon dioxide and methane actually lag (come after) the changes in temp. by hundreds of years, which would seem to refute the hypothesis that increases in greenhouse gases caused temperature changes. Physical reason why= feedback mechanism in which as oceans warm, the amount of dissolved gases they can hold decreases. Thus CO2 and methane are released from oceans into the atmosphere and levels of these greenhouse gases in the atmosphere increases- Points to make from the Pleistocene epoch:o We are still in a glacial period in which earth in oscillating between glacial and interglacial conditionso Peaks of glaciates occurring every 100,000 years or soo During peak glacial periods, global avg temps 5-10 degrees C than today, vast portions ofnorthern continents covered by ice sheets, atmospheric CO2 concentrations= 200ppmo Cold intervals separated by warmer, shorter intervals (interglacial’s) where average temperatures warmer, and continental glaciation limited to Greenland and antartica, atmospheric CO2 concentrations= 280ppm. (due to human activity CO2 concentration is now 400ppm which is much higher)o We are currently in warmer interglacial period (Holocene epoch) began 15,000 years agoo If glacial cycle continues, peak glaciations of next ice age expected to occur in 85,000 yearso Current ice age cycles triggered by small, regular changes in the way earth orbits the sun(however are insufficient to explain ice ages, must be positive feedback that amplify the effects of the slight orbital changes)- Slight variations in the earths orbital parameters have resulted in significant climate changeso Paleoclimates perspective= climate change is normal and part of the earths natural variability related to interactions among the atmosphere, ocean, and land as well as changes in the amount of solar radiation reaching earth.o Major cycles in earths orbital parameters: Eccentricity= variations in shape of the orbit from less elliptical to more elliptical (period of about 100,000 yrs)- The more elliptical, the larger the difference in solar radiation between farthest and closest approach of the sun- Varies between circular to 6%