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 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 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 1995-2003

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”)• 900-1300 AD – Medieval Warm Period• 1300-1450 Little Ice Age I• 1450-1550 Partial Recovery• 1550-1800 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

• CO2 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 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 costly

Claims that human activities have no effect on climateClaims that no long term climate changes are occurring at allClaims that the earth is actually cooling