Chapter 15: Air, Weather, and Climate

15.1 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 it

Atmospheric Circulation

Climate Versus Weather

Climate is what you expect and weather is what you get

15.2 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 damage

Why It Rains Water Evaporates Out of Oceans – Minor Contribution from Lakes, Rivers, Land – About 13,000 km 3 of water in atmosphere (> Lake Superior) – Only 1 ppm of total surface water Condenses as Clouds – A 1 km 3 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 Droplets

The Coriolis Effect

Not a Manifestation of the Coriolis Effect! Too small scale for the Coriolis Effect to be significant

15.2 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 damage

Fronts and Low Pressure Systems

World Hurricane Tracks

15.3 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 policymakers

Post Ice-Age Climate 11,000 Younger Dryas Cooling 9,000-6,000 Mid-Holocene Warm Period (“Climatic Optimum”) AD – Medieval Warm Period Little Ice Age I Partial Recovery Little Ice Age II

15.4 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 CO 2 is the most important of many factors Most Important Greenhouse Gas is Water Vapor Explain How Increasing Greenhouse Gases Will Not Cause Warming

15.5 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 Costs

Possible 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 Value

15.6 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 Emissions

What 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 Skepticism Concerns about failure to modeled features like cloud cover Too many assumptions have to be built into climate models Concerns about the way global climate data are measured How to link recent instrument data with older historical and prehistoric climate indicators? Concerns about the validity of computer modeling of climate in general Are recent climate changes man-made, or natural? Claims that warming of the climate might actually be beneficial Claims that climatic change is too far along to reverse or mitigate Claims that attempts to control climate change would be too costly Claims that human activities have no effect on climate Claims that no long term climate changes are occurring at all Claims that the earth is actually cooling