Chapter 15: Air, Weather, and Climate15.1 The Atmosphere Is A Complex SystemSlide 3Atmospheric CirculationClimate Versus WeatherClimate is what you expect and weather is what you get15.2 Weather Events Follow General PatternsWhy It RainsThe Coriolis EffectSlide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Not a Manifestation of the Coriolis Effect!15.2 Weather Events Follow General PatternsFronts and Low Pressure SystemsWorld Hurricane Tracks 1995-200315.3 Natural Climate VariabilityPost Ice-Age Climate15.4 How Do We Know Recent Climate Change Is Human-caused?Slide 35Possible Effects of Global Warming15.6 Envisioning SolutionsWhat We Know and Don’t KnowThe Spectrum of SkepticismSlide 40Chapter 15: Air, Weather, and Climate15.1 The Atmosphere Is A Complex System•Absorbed solar energy warms our world –Mostly Stored in the Oceans•The greenhouse effect is energy capture by gases in the atmosphere–“A Little Greenhouse Effect is a Good Thing”•Evaporated water stores energy, and winds redistribute itAtmospheric CirculationClimate Versus WeatherClimate is what you expect and weather is what you get15.2 Weather Events Follow General Patterns•Why does it rain? •The Coriolis effect explains why winds curve •Ocean currents modify our weather •Billions of people rely on seasonal rain •Frontal systems create local weather •Cyclonic storms can cause extensive damageWhy It Rains•Water Evaporates Out of Oceans–Minor Contribution from Lakes, Rivers, Land–About 13,000 km3 of water in atmosphere (> Lake Superior)–Only 1 ppm of total surface water•Condenses as Clouds–A 1 km3 cloud contains a few million kg of water•Collision of Cloud Droplets is too Slow•Bergeron Process–Water Evaporates off Ice Crystals and Condenses on Water DropletsThe Coriolis EffectNot a Manifestation of the Coriolis Effect!•Too small scale for the Coriolis Effect to be significant15.2 Weather Events Follow General Patterns•Why does it rain? •The Coriolis effect explains why winds curve •Ocean currents modify our weather •Billions of people rely on seasonal rain •Frontal systems create local weather •Cyclonic storms can cause extensive damageFronts and Low Pressure SystemsWorld Hurricane Tracks 1995-200315.3 Natural Climate Variability•Climates have changed dramatically throughout history •Earth’s movement explains some cycles •El Nifio is an ocean-atmosphere cycle •Recent changes are unusually rapid •The IPCC assesses data for policymakersPost Ice-Age Climate•11,000 Younger Dryas Cooling•9,000-6,000 Mid-Holocene Warm Period (“Climatic Optimum”)•900-1300 AD – Medieval Warm Period•1300-1450 Little Ice Age I•1450-1550 Partial Recovery•1550-1800 Little Ice Age II15.4 How Do We Know Recent Climate Change Is Human-caused? •The IPCC finds overwhelming evidence of anthropogenic climate change –Argument from Authority–Read the Scientific Literature•CO2 is the most important of many factors•Most Important Greenhouse Gas is Water Vapor•Explain How Increasing Greenhouse Gases Will Not Cause Warming15.5 What Are The Effects Of Climate Change, And Should We Care? •Global warming will be costly; preventing it might not be •Flooding, drought, storms, and disease are key risks •Some People Argue for Benefits–Longer Growing Seasons–More Habitable Land–Reduced Energy CostsPossible Effects of Global Warming•More Heat Extremes•Drought•Rise in Sea Level•Temporary Severe Cold Spell?•Rapid Migration of Ecological Zones•More Biomass but Lower Nutritional Value15.6 Envisioning Solutions•The Kyoto Protocol called for a 5 percent reduction in carbon emissions •Stabilization wedges could work now •Alternative practices can be important •Regional initiatives are emerging •What Can You Do? Reducing Carbon Dioxide EmissionsWhat We Know and Don’t Know•Certain: Carbon Dioxide Increase•Nearly Certain: Climate is Warming•Debatable (Legitimately)–How much is of human origin?–Permanent or temporary warming?•Uncertain:–Can we do anything?–Will benefits exceed costs?–Risks of premature policy decisions?The Spectrum of SkepticismConcerns about failure to modeled features like cloud coverToo many assumptions have to be built into climate modelsConcerns about the way global climate data are measuredHow to link recent instrument data with older historical and prehistoric climate indicators?Concerns about the validity of computer modeling of climate in generalAre recent climate changes man-made, or natural?Claims that warming of the climate might actually be beneficialClaims that climatic change is too far along to reverse or mitigateClaims that attempts to control climate change would be too costlyClaims that human activities have no effect on climateClaims that no long term climate changes are occurring at allClaims that the earth is actually