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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
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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
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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