Chapter 23: The Atmosphere, Climate and Global Warming

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Transcript Chapter 23: The Atmosphere, Climate and Global Warming

Chapter 23: The Atmosphere,
Climate and Global Warming
The Origins of the Global
Warming Issue
• Concern arises from two kinds of evidence:
– Increase in average surface temperature of the
Earth from 1860 to the present
– Increase in carbon dioxide concentrations in the
atmosphere.
• Measured on Mauna Loa in Hawaii by Charles
Keeling
The Origins of the Global
Warming Issue
• Relationship between chemistry of planet’s
atmosphere and planet’s surface
temperature.
– Certain gases trap heat energy and warm the
plant
– Since this idea was first introduce has stirred
controversy
The Atmosphere
• Thin layer of gases that envelops Earth.
– Held near the surface by gravitation and pushed
upward by thermal energy.
– Primarily nitrogen (78%), oxygen (21%), argon
(0.9%), carbon dioxide (0.03%) and water
vapor.
– Trace amounts of other gases/pollutants
– Dynamic system
Structure of the Atmosphere
• Made up of several vertical layers
– Troposphere- bottom layer
• Where weather occurs
• Temperature decrease w/ elevation
• At the top is tropopause- acts as a lid
– Stratosphere- above the troposphere
• Stratospheric ozone layer just above the tropopause
• Protects again UV radiation
Atmospheric Processes
• Two important qualities of the atmosphere
are pressure and temperature.
• Pressure is force per unit area.
– Caused by the weight of overlying atmospheric
gases on those below
– Decreases w/ altitude
– Low pressure systems usually bring clouds
– High pressure systems usually bring clear skies
Atmospheric Processes
• Temperature is the relative hotness or
coldness of materials
– Measure of thermal energy
• Water vapor content another important
characteristic
– Varies from 1% to 4%
Atmospheric Processes
• Atmosphere moves because of the Earth’s
rotation and differential heating.
– Produce global patterns of prevailing winds and
latitudinal belts of high and low pressure
What Makes the Earth Warm
• Almost all the energy from the sun.
• Sunlight comes in a wide range of
electromagnetic radiation.
– Long to short wavelengths
– Most of the radiation that reaches the Earth is in
the infrared and visible wavelengths
What Makes the Earth Warm
• Under typical conditions Earth’s
atmosphere
– Reflects about 30% of the electromagnetic
energy that comes in from the sun
– The atmosphere absorbs about 25%
– The remaining 45% gets to the surface
• Radiates back to the atmosphere or into outer space
Weather and Climate
• Weather is what’s happening now w/ the
atmosphere near the ground.
– Its temperature, pressure, cloudiness,
precipitation, winds
• Climate is the average weather
– Usually refers to long periods of time
– Classified mainly by latitude and wet/dry
The Climate is Always Changing
• Climate has warmed and cooled may times
in Earth’s history
– Times of high temp involve relatively ice free
periods
– Times of low temp involve glacial events
Causes of Climate Change
• It wasn’t until the 19th century that scientists
began to understand that climate changed
greatly over long periods and included
times of continental glaciations.
– Evidence was debris at the edges of existing
glaciers which is the same kind found deposited
at lower elevations.
Causes of Climate Change
• Why does climate change?
– Explanation might have to do w/ the way the Earth
revolves on its axis and rotates around the sun.
• Earth is like a wobbling top following an elliptical
orbit around the sun.
• Three kinds of changes occur.
– (1) Earth is unable to keep its poles at a constant angle
in relation to the sun. The wobble makes a complete
cycle in 26,000 years.
Causes of Climate Change
– (2) The tilt of wobble also varies over a period
of 41,000 years
– (3) The elliptical orbit around the sun also
changes. Sometimes it is a more extreme
ellipse; other times it is closer to a circle and
this occurs over 100,000 years.
Causes of Climate Change
• The combination of these lead to periodic
changes in the amount of sunlight reaching
the Earth.
– Milankovitch showed that these variations
correlated w/ the major glacial and interglacial
periods.
– Called Milankovitch cycles
– Don’t account for all climate variations
Solar Cycles
• The Sun Goes Through Cycles Too
– Sometimes hotter, sometimes cooler
– Documented by differing amounts of isotopes
trapped in glacial ice
• Appears that variability of solar input of
energy explains some of the climatic
variability too.
Atmospheric Transparency
Affects Climate and Weather
• How transparent the atmosphere is to
radiation coming into it affects the temp of
the Earth
– From the sun and from the Earth’s surface
• Dust and aerosols absorb light
– Volcanoes, forest fires and farming put dust
into the atmosphere
– Chemical and physical comp of atmosphere can
make it warmer or cooler
The Green House Effect
• Each gas in the atmosphere has its own
absorption spectrum
– Certain gases are especially strong absorbers in
the infrared
– They absorb radiation emitted by the warmed
surfaces of the Earth
– They then re-emit this radiation
– Making the Earth’s surface warmer
The Green House Effect
• Effect called the greenhouse effect
– Natural phenomenon
• Major green house gases are
–
–
–
–
–
Water vapor
Carbon dioxide
Methane
Some oxides of nitrogen
CFCs
The Roles of Major Greenhouse
Gases In Affecting Climate
• Nobody doubts that the greenhouse effect exists
and affects planets.
• The puzzle arises on the Earth about relative
importance of greenhouse gases in affecting
climate.
• Evidence indicates that carbon dioxide, methane,
and temperature rise and fall together.
– From this most scientists conclude that greenhouse
gases are causing climate change.
Positive and Negative Feedbacks
• The atmosphere and its interactions w/ the
ocean and land surfaces experience positive
and negative feedbacks.
• Negative feedback
– Warms temps warm air and lead to increased
evaporation
– Evaporation leads to more cloud formation
which reflects more sunlight which could cool
the surface.
Positive and Negative Feedbacks
• Positive feedback
– Warms temps warm air and lead to increased
evaporation but instead of clouds forming
remain as water vapor.
– Water vapor is a greenhouse gas. The warmer it
gets the more water vapor, and the process
continues.
The Ocean’s Effect on Climate
Change
• Water has the highest heat capacity of any
compound.
– Large amount of heat energy can be stored in
oceans
• Ocean can absorb CO2
– As CO2 increases in atmosphere it also
increases in the oceans
The Ocean’s Effect on Climate
Change
• Part of what drives the climate system is the
ocean conveyor belt.
– A global circulation of ocean waters
– If the conveyor was shut down, major changes
in climate would occur.
El Niño and Climate
• El Niño refers to a certain kind of periodic
variation of currents in the Pacific Ocean.
• Under non-El Niño conditions
– Trade-winds blow west across the tropical
Pacific
– Warm surface water pile up in W. Pacific
El Niño and Climate
• During El Niño years
– Trade winds weaken
– Western moving current weakens or reverses
– As a result eastern equatorial ocean unusually
warm
– High rates of precipitation and flooding in Peru
• Changes global atmospheric circulation
– Causes changes in weather in regions that are far
removed from tropical Pacific
El Niño and Climate
• Rise in temp of sea surface waters off the
SA coast inhibits the upwelling of nutrientrich cold water from deeper levels.
– Upwelling releases carbon dioxide
– El Niño events reduce the amount of oceanic
carbon outgassing
Predicting the Future of the
Climate
• For climate and its effects on living things ,
there are two ways to forecast the future:
– Empirical and theoretical
• Empirical approach is to go back to the
geological idea of uniformitarianism
– Has led to the extensive research on climates
and atmospheric conditions of the past
Predicting the Future of the
Climate
• Empirical problem we face is temperature
records recent and not widespread.
– Expects have to find ways to extrapolate,
interpolate and estimate
– Places like Hadley Meteorological Center in
Great Britain
• Reconstructing temp records
Predicting the Future of the
Climate
• Computer simulation
– The second method to forecast climate changes
is to develop computer models of the world
climate.
– All based around the atmosphere being divided
into rectangular solids
• Each a few km high and several km N or S
• For each the flux of energy and matter is calculated
to each adjacent cell
Predicting the Future of the
Climate
• These global climate models are called
“general circulation models” (GMCs) by the
climatologist that develop them.
– Crude compared to real world
– And determining how well they work is a major
challenge
What a Global Warming World
Might be Like
• Global surface temp has increased
0.2°C/ decade in the past 30 years.
– Since 1998, the eight warmest years have
occurred.
– Continued warming of 0.2°C /decade is
projected.
What a Global Warming World
Might be Like
• By 2030 the concentration of CO2 in the
atmosphere will have doubled from pre–
Industrial Revolution concentrations.
– The average global temperature will have
risen approximately 1° to 2°C
– W/ greater temperature increases toward
the poles.
• Polar amplification
Potential Environmental, Ecological,
and Human Effects of Global
Warming
• Changes in River Flow
– Melting of glacial ice and reductions in snow
cover are anticipated to accelerate throughout
the twenty-first century.
– Rainfall will likely increase, but runoff will be
more rapid than if snow slowly melts.
• Reservoirs will fill sooner and more water will
escape to the ocean.
Potential Effects of Global Warming
• Rise in Sea Level
– A major warming could increase sea levels
because of
• 1. Expansion of liquid water as water warms
• 2. Melting of ice sheets on land whose waters then
flow into the ocean.
– About half the people on Earth live in the
coastal zone.
– Sea level and population rising, the number of
people vulnerable to coastal flooding increases.
Potential Effects of Global Warming
• Rise in sea level could:
– Threatens island nations
– Increase coastal erosion on open beaches and
cause property loss.
– Cause landward progression of estuaries and
salt marshes
– Lead to lost of coastal wetlands
– Threaten ground water supply in coastal
communities
Potential Effects of Global Warming
• Glaciers and Antarctic Ice Cap
– Many more glaciers in the world are retreating
than advancing.
– Not all due to global warming
• E.g. Mt. Kilimanjaro
– Northern Hemisphere sea ice coverage has
declined an average of 10.7% / decade since
1970s
Potential Effects of Global Warming
• The central ice cap on Antarctica is growing
– This is consistent w/ prediction of global
climate change models.
– As Earth warms, more snow falls on Antarctica.
• The rate of melting of the Greenland ice
sheet has doubled since about 1998.
Potential Effects of Global Warming
• Changes in Biological Diversity
– The Intergovernmental Panel on Climate
Change (IPCC) report states that
• “approximately 2–20% of species assessed so far are
likely to be at increased risk of extinction as global
mean temperatures exceed a warming of 2 to 3°C
above preindustrial levels.”
Potential Effects of Global Warming
• Black guillemots
– Birds that nest on Cooper Island, Alaska,
• The abundance of this species has decreased.
– Recession of sea ice occurred before chicks were
mature enough to survive on their own.
– Parent birds feed on Arctic cod found under the sea ice.
• Distance from feeding grounds to nest must be <30 km
• In recent years, been s much as 250 km from the island
• As a result, lost an important source of food.
Potential Effects of Global Warming
• Agricultural Productivity
– Globally, agriculture production is likely to
increase in some regions and decline in others.
– A climate shift could have serious negative
effects on mid-latitude food production.
– In addition, lands in the southern part of the
Northern Hemisphere may become more arid.
• soil moisture relationships will change.
Potential Effects of Global Warming
• Human Health Effects
– Health status of millions of people could
potentially be affected through
• Increases in malnutrition
• Increased deaths, diseases, and injury due to
extreme weather events
• Increased burden of diarrhoeal diseases
• Increased frequency of cardio-respiratory diseases
Adjusting to Potential Global
Warming
• There are two kinds of adjustments people
can make to the threat of global warming:
– Adapt: Learn to live with future global climatic
change.
– Mitigate: Work to reduce emissions of
greenhouse gases.
Adjusting to Potential Global
Warming
• How can carbon dioxide emissions be
reduced?
– Energy planning that relies heavily on energy
conservation and efficiency
– Use of alternative energy sources, use of natural
gas
– Use of mass transit
– Greater economic incentives to energy-efficient
technology, higher fuel-economy
Adjusting to Potential Global
Warming
• Burning forests to convert land to agricultural
– Accounts for about 20% of anthropogenic emissions of
carbon dioxide into the atmosphere.
– Minimizing burning and protecting the world’s forests
would help reduce the threat of global warming.
• Reforestation
– Planting more trees
– Increase biospheric sinks for carbon dioxide.
Adjusting to Potential Global
Warming
• Geologic sequestration of carbon is another
possible mitigation measure.
– The idea is to capture carbon dioxide from
power plants and industrial smokestacks.
– Compressing the gas and changing it to a
mixture of both liquid and gas and then
injecting it deep underground.
– Have the potential to sequester as much as
1,000 gigatons of carbon.
International Agreements to
Mitigate Global Warming
• Two major approaches are:
– international agreements in which each nation
agrees to some specific limit on emissions
– Carbon trading
International Agreements to
Mitigate Global Warming
• In carbon trading, a nation or nation agrees
to a cap of carbon emissions.
– Then corporations and other entities are issued
emission permits, allowing a certain quantity of
emissions.
– These can be traded.
International Agreements to
Mitigate Global Warming
• First international meeting to discuss
limiting greenhouse gases held in Toronto,
Canada in 1988.
• In 1992, Earth Summit in Rio de Janeiro,
Brazil.
– General blueprint for reduction of global
emissions suggested
– US thought it would be to costly and no legally
binding limits set.
International Agreements to
Mitigate Global Warming
• In 1997, legally binding limits discussed in
Kyoto, Japan.
– US eventually agreed to cut emissions to 7%
below 1990 levels (leading scientists
recommend cuts 60-80% below)
– Became a formal treaty in 2006