1Climate and Climate ChangeWeather vs. Climate Natural Climate Variations:e.g. the Ice Ages 1Human Influences on Climate:Global WarmingWeather vs. ClimateWeather: Short-term variations in temperature, precipitation, wind, etc.Day to day, month to month, year to yearClimate: Essentially the average of weather over an extended period of time.i.e. What is typical or what is“normal”for a specific place2i.e. What is typical or what is normal for a specific placeIncludes both the mean values and the typical range of variabilityDescribed mainly by :• Temperature average, maximum, minimum, seasonal variations, etc.• Precipitationaverage, maximum, minimum, seasonal variations, etc.The 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 (oceans, rivers, lakes), solid Earth, biosphere, and cryosphere (ice and snow)3)Is highly dynamicInvolves many processes and factors that can affect each other in complex ways (e.g. feedbacks)Long-Term Climate Variations – The Ice Ages4Maximum extent of ice in the Northern Hemisphere during the last glacial periodGlacials and InterglacialsThe deep sea record5WarmerFig. 15.32 – Understanding EarthColder6Glacials and InterglacialsIce core recordfrom Box 15.2 – Understanding Earth27Glacials and InterglacialsGlacial lakes (pluvial record)Animations next:• expanding ice sheets during glacial time• rising sea level during interglacial time• Ice sheets + sea level change (and other animations):http://emvc.geol.ucsb.edu/forteachers/forteachers.htmCauses of the glacial-interglacial cyclesAny successful theory to explain the Ice Ages must account for • Overall cooling of Earth and widespread formation of glaciers• Glacial-Interglacial cyclesProposed possible causes for long-term climate changes:• Changes in the arrangement of the continents•Changes in oceanic circulation8Changes 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 orbitMilankovitch cyclesShape (eccentricity) of the Earth's orbit – 100,000 year cycleAngle of Earth's axis (obliquity or 9tilt) changes – 41,000 year cycleAxis wobble (precession) – 23,000 year cycleMilankovitch cycles10Fig. 15.32 – Understanding EarthAtmospheric CO2Concentrations With Time11Graphic modified from: Brook, 2005, Tiny Bubbles Tell All: Science v. 310 no. 25 pp. 1285-1287.12Increase 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 have resulted in dramatic increases in energy use over time.3Observed climate changes and effects: - Warmer average air temperatures, especially in the Arctic13- Melting tundra & permafrost (both alpine and arctic)Increasing concentrations of several heat-trapping gasses (“greenhouse gases”) results in a stronger greenhouse effect with a variety of consequences:py- Warmer oceans- Rising sea level- Shrinking glaciers- Less arctic sea ice- More extreme weather events including more heat waves- Stronger hurricanes?- Extinction of mountaintop speciesp)- Plants leafing and flowering earlier in the spring- Snow melt beginning earlier in the spring- Shifting distributions of many species- Changes in breeding and migration patterns of many species- Much more…Other effects: e.g. ocean acidification (from CO2dissolving in the oceans)Warming atmosphere• Average global temperatures have increased by ~1oC in the last 150 years.14Warming oceans and rising sea level15From: Moore et. al, 2005 New Tools for Analyzing Time Series Relationships and Trends EOS 86, 24 http://www.agu.org/pubs/eos/eo0524.shtmlTrend in global sea surface temperatures relative to 1961–1990 average.Change in mean sea level at Brest, France.Tan shading is the 95% confidence interval of the nonlinear trends. Shrinking glaciersMcCarty Fjord in Kenai Fjords National Park190916Photos by Bruce Molnia, U.S. Geological Survey2004 The glacier has retreated by more than 10 milesTime-lapse video of retreating Columbia Glacier in Alaska: http://environment.nationalgeographic.com/environment/global-warming/extreme-ice-survey-article.htmlShrinking and thinning sea iceExtend of artic sea ice at the end of summer17Image source: NASAhttp://www.agu.org/journals/eo/eo0937/2009EO370006.pdf#anchorClimate feed-back mechanisms Possible outcomes of altering the climate-systemTwo types • Positive-feedback mechanisms reinforce the initial change• Negative-feedback mechanisms produce results that are just the opposite of the initial change and tend to offset it Examples: 18p• Melting of snow and ice as a result of increased temperatures reduces the reflectivity (albedo) of the earth’s surface• The expansion of ice sheets during a cooler or wetter climate increases the albedo• Warming of arctic areas and oceans may release more methane• More evaporation of water into the air leading to more cloudsWhat type of feedback would result from each of these?4Future warming? Fig. 16.11 Keller, Environmental Geology• Globally averaged surface temperature is projected to continue increasing• By the year 2100, the total warming may be 1.4 to 5.8ºC• This magnitude of change is similar to the difference between glacial and interglacial periods19Red line = measured temperature variationsSome future consequences of global warming Temperature patterns will continue to change: Even though global temperatures would be warmer on average, some specific areas could become colder, and others will warm by much more than the average change.Glaciers and sea ice will continue to meltGlobal mean sea level will continue to rise20Distribution of the world’s water resources will change: Some places will become wetter, and others will become drier. This will change the productivity of agricultural regions potentially affecting global food supplies.Weather patterns will change: • Higher frequency and intensity of hurricanes??? • Shifts in the paths of large-scale storms• Changes in frequency and intensity of heat waves and droughtsWhat can we do?What should we do?1. Research to better understand