1Climate and Climate ChangeWhat is weather? What is climate? Natural Climate Variations:Ice Ages 1Human Influences on Climate:Global WarmingWeatherDay-to-day variations in temperature, precipitation, wind, etc.Also includes variations that can persist for one to a few years:th t i ld th2e.g. a year that is colder than averagea year that is warmer than averagea year that is wetter or drier than averageClimateA long-term average (5-10 years or more)The most important elements used to describe climate are • Temperature (average, maximum, minimum, seasonal variations, etc.)P i it ti(iii lii)3•Precipitation (average, maximum, minimum, seasonal variations, etc.)So, climate is the average of weather over an extended period of time.It includes both the mean and the typical range of variabilityThe Climate SystemIncludes a lot more than just the atmosphereThe climate system as a whole involves the exchanges of energy and moisture among the atmosphere, hydrosphere, solid Earth, biosphere, and cryosphere (ice and snow)4Is highly dynamicInvolves many processes and factors that can affect each other in complex waysTypes of Climates: ClassificationEvery place on Earth has a unique climate.Climates often are grouped and classified using monthly and annual average values of temperature and precipitation• Five principal climate groups• Humid tropical – includes tropical rain forest•Dry –includes deserts5y• Humid middle-latitude with mild winters• Humid middle-latitude with severe winters•Polar• Precipitation is the key distinguishing factor for dry climates. The others are defined on the basis of temperature characteristics.• Mapped boundaries were originally based largely on the distribution of groups of plants since vegetation is a good indicator of typical conditions.Climates of the world62Long-Term Climate Variations – The Ice Ages• The most recent Ice Age period began 2 to 3 million years ago • Most of this time is included in the Pleistocene epoch (about 1.8 million to 10,000 years ago)• The Ice Ages include glacial and interglacial periods:• Glacials: wide-spread ice7• Interglacials: less ice –Today’s climate is that of an interglacial• During the last glacial maximum:• ice covered 30% of Earth's land area• sea level was about 100 meters (330 feet) lower than todayMaximum extent of ice in the Northern Hemisphere during the Ice AgeGlacials and InterglacialsThis figure illustrates the relative changes in the oxygen isotope composition (varying proportion of the heavier and rarer oxygen-18 isotope relative to the more common oxygen-16 isotope) of foraminifera from deep sea sediment cores. The changes reflect both ocean surface temperature variations and variations in the oxygen isotope composition of sea water.8Fig. 15.32 – Understanding EarthIce Core RecordsIce cores taken from thick continental ice sheets in Greenland and Antarctica reveal important information about ice age climate variations. Changes in the isotopic composition of precipitation, changes in the composition of the atmosphere (e.g. carbon dioxide content), and volcanic activity are important parts of the ice core records.9from Box 15.2 –Understanding EarthPluvial Lakes during the last glacial maximum• Lake Bonneville, the largest Pluvial lake in the Great Basin, was at a maximum depth of more than 300 meters (1000 ft) roughly 15,000 years ago• These lakes reflect a somewhat cooler and wetter ice age 10climate in this region compared to the modern climate• Sediments deposited in these lakes record changes in lake level, and are an important part of the world record of climate changeClimate Variations – The Ice AgesAnimations:• expanding ice sheets during glacial time11• rising sea level during interglacial time• Ice sheets + sea level change (and other animations):http://emvc.geol.ucsb.edu/forteachers/forteachers.htmCauses of the Ice Ages Any successful theory to explain the Ice Ages must account for • Overall cooling of Earth and widespread formation of glaciers• Glacial-Interglacial cyclesProposed possible causes • Changes in the arrangement of the continents•Changes in oceanic circulation12Changes in oceanic circulation • Variations in Earth's orbit • Milankovitch hypothesis • Shape (eccentricity) of Earth's orbit varies • Angle of Earth's axis (obliquity) changes • Axis wobbles (precession)Changes in climate during the last several hundred thousand years are closely associated with variations in Earth's orbit3Milankovitch cyclesShape (eccentricity) of the Earth's orbit – 100,000 year cycleAngle of Earth's axis (obliquity or 13tilt) changes – 41,000 year cycleAxis wobble (precession) – 23,000 year cycleGlobal Climate Change (a.k.a. Global warming)• Greenhouse gases in the atmosphere are increasing, and this makes the natural greenhouse effect stronger• Water vapor and carbon dioxide absorb heat and are responsible for most of the greenhouse effect• Burning fossil fuels has released great quantities of carbon dioxide • Other trace gasses including methane, nitrous oxide, and some chlorofluorocarbons (CFCs) also add to the greenhouse effect.khhifffhh bl14•Taken together, the warming effects of these other gases may be nearly as great as carbon dioxide.• “Global warming” is often used in reference to the changes that result from the stronger greenhouse effect, but more is going on than just increasing temperatures.The significant impact of human activities that we see today is nothing new. People have been modifying the environment over large areas for thousands of years. However, the extent and magnitude of the changes continues to increase.Atmospheric CO2Concentrations With Time15Graphic modified from: Brook, 2005, Tiny Bubbles Tell All: Science v. 310 no. 25 pp. 1285-1287.16Increase in Atmospheric CO2Concentrations With TimeSee also: http://www.eia.doe.gov/emeu/aer/eh/frame.htmlU.S. Energy Consumption by Source, 1635-2000Industrialization and population growth resulted in dramatic increases in energy use in the U.S. over time.Why are levels of greenhouse gases rising? Carbon dioxide - CO2• Burning massive quantities of fossil fuels (coal, oil, natural gas) which has put billions of tons of CO2into the atmosphere• Clearing (and sometimes burning) of millions of acres of forests every year• Loss of organic matter from soils due to agricultural practicesMethane – CH4• Release of methane from the ground due