Download 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
Structure of the Atmosphere
• Made up of several 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
• Pressure and temperature – These
components of atmosphere are physically
related to one another.
• 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
• 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
Weather and Climate
• Weather is what’s happening now w/ the
atmosphere near the ground.
– Its temperature, pressure, cloudiness,
precipitation, winds – Very LOCAL
• Climate is the average weather – GLOBAL
and Regional
– Usually refers to long periods of time
– Classified mainly by latitude and amount of
precipitation
The Climate is Always Changing
• Climate has warmed and cooled many 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
• Three kinds (non-anthropogenic) of changes occur
to cause climate change:
– (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.
– (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 composition 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
• Coined because of the way a greenhouse
traps heat
• 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 warmer it gets, the more people use their
AC – thus increasing demand for electricity that
increases CO2 levels and temperature
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 (increasing acidity – or
“lowering” the pH)
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 because of the capacity
the ocean have to “move” heat from one part of
the planet to another
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 being
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 (west side near Peru and Ecuador)
inhibits the upwelling of nutrient-rich cold
water from deeper levels.
– Upwelling releases carbon dioxide
– El Niño events reduce the amount of oceanic
carbon out-gassing
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 ten 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
Artic sea ice coverage receding sequentially
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 (a
physical relationship)
• 2. Melting of ice sheets on LAND whose waters
then flow into the ocean. (This is unlike sea ice
melt)
– 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 its been as much as 250 km from the island
• As a result, birds 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.
(United States and much of Brazil)
– In addition, lands in the southern part of the
Northern Hemisphere may become more arid.
• soil moisture 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 (Dysentery)
• 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 were 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
– US did not want to sign because it allowed
developing countries to pollute “at will”
without penalty