Ch 4. The three modern global change problems.

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Ch 4. The three modern global change
problems.
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• Earth has been changing and will continue to do
  so. It is changing faster today than it ever has.
  The major reason is human activity.
• Ozone depletion Ozone hole in South Pole
• deforestation
• Greenhouse gases and global warming

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• Ozone
• source O and O2 makes it through chemical
  process.
• Location in middle-layer atmosphere
  (stratosphere).
• roles absorb ultraviolet radiation from
  Sun.

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Vertical Structure of the Atmosphere
4 distinct layers determined by the change
of temperature with height
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• Ozone depletion describes two distinct, but
  related observations
• (1) a slow, steady decline of about 4 per
  decade in the total volume of ozone in Earth's
  stratosphere (ozone layer) since the late 1970s,
• (2) a much larger, but seasonal, decrease in
  stratospheric ozone over Earth's polar regions
  during the same period.

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• Ozone ( ) is a form of oxygen, and protects
  the earths surface from Suns harmful
  ultraviolet radiation. Ozone depletion is the
  result of a complex set of circumstances and
  chemistry .

• Antarctic Ozone Levels in Fall 2003
• The ozone hole is represented by the purple, red,
  burgundy, and gray areas that appeared over
  Antarctica in the fall of 2003. The ozone hole is
  defined as the area having less than 220 Dobson
  units (DU) of ozone in the overhead column (i.e.,
  between the ground and space).

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Image of the largest Antarctic ozone hole ever
recorded (September 2006).
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Ozone over Antarctic during Oct.
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• Mean total ozone over Antarctica during the month
  of October

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• It shows a sharp drop beginning in the early
  1970s. The graph to the left shows long-term
  ozone levels over Arosa, Switzerland. Although
  ozone levels rise and fall in natural cycles, the
  average level remained constant from 1926 until
  1973. Beginning in 1973, however, and continuing
  through 2001, ozone levels have dropped at a rate
  of 2.3 percent / decade.

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• Too much ultra-violet light can result in
• Skin cancer
• Eye damage such as cataracts
• Immune system damage
• Reduction in phytoplankton in the oceans that
  forms the basis of all marine food chains
  including those in Antarctica.
• Damage to the DNA in various life-forms. So far
  this has been as observed in Antarctic ice-fish
  that lack pigments to shield them from the
  ultra-violet light (they've never needed them
  before)
• Probably other things too that we don't know
  about at the moment.

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• Global warming is the serious problem because
• It affects the greatest number of people
• Migration of marine animals could result
• Rising sea level could result
• Cold climate species might die
• Ozone depletion and deforestation are both
  confined to particular areas whereas global
  warming is truly global

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• Global warming is the serious problem because
• It affects the greatest number of people
• Migration of marine animals could result
• Rising sea level could result
• Cold climate species might die
• Ozone depletion and deforestation are both
  confined to particular areas whereas global
  warming is truly global

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• Why does a ozone hole form over Antarctica?
• The ozone hole is caused by the effect of
  pollutants in the atmosphere destroying
  stratospheric ozone. During the Antarctic winter
  something special happens to the Antarctic
  weather.
• Firstly, strong winds blowing around the
  continent form,
• this is known as the "polar vortex" -  this
  isolates the air
• over Antarctica from the rest of the world.
• Secondly, clouds form called Polar
  Stratospheric
• Clouds. Clouds turn out to have the effect
  of
• concentrating the pollutants that break down
  the ozone,
• so speeding the process up.

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Deforestation
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Deforestation affects Carbon balance Hydrological
cycle Radiative energy balance Biodiversity
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Statistics
It has been estimated that about half of the
earth's mature tropical forests between 7.5
million and 8 million km2 of the original 15
million to 16 million km2 , have now been
cleared since 1947.

• North America and Europe already done

• 85 of old growth forests in US destroyed by
  settlers most replanted

• Parts of Pacific NW and Alaska deforesting now
  as fast as Brazil

Canada One case of deforestation in Canada is
happening in Ontario's boreal forests, near
Thunder Bay, where 28.9 of a 19,000 km² of
forest area had been lost in the last 5 years
and is threatening woodland caribou. This is
happening mostly to supply pulp for the facial
tissue industry. In Canada, less than 8 of the
boreal forest is protected from development and
more than 50 has been allocated to logging
companies for cutting.
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Tropical Rainforest
Earth's most complex biome in terms of both
structure and species diversity abundant
precipitation and year round warmth. Climate
Mean monthly temperatures are above 64F
precipitation is often in excess of 100 inches a
year. Vegetation 100 to 120 feet tall
canopy. Soil infertile, deeply weathered and
severely leached. Red color because of high iron
and aluminum oxides. Fauna Animal life is highly
diverse Distribution of biome 10N and 10S
latitude. Neotropical (Amazonia into Central
America), African (Zaire Basin with an outlier in
West Africa also eastern Madagascar),
Indo-Malaysian (west coast of India, southeast
Asia)
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• Tropics

• Rainforests 50 years ago covered 14 of the
  world's land surface and have been reduced to 6,
  and that all tropical forests will be gone by the
  year 2090

• Brazil slash and burn Amazon 200 increase
  in deforested area from 1979 - 1988

Some scientists have predicted that unless
significant measures (such as seeking out and
protecting old growth forests that have not been
disturbed) are taken on a worldwide basis, by
2030 there will only be ten percent remaining.
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The problem

• Disappearing at a rate of tens of thousands of
  square miles per year

• Land clearing in developing countries for
  farming and ranching (e.g., Brazil)

• Wood as a fuel (e.g., 90 of Africans use wood
  as primary fuel)

• Ballooning populations in developing countries

• Loss of fauna associated with the forests

• Current extinction rate of 50,000 species per
  year

• Rate reflects fact that most fauna and flora in
  tropics are disappearing

• Loss of soil value for farming (formation of
  laterites)

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Effects

• Lowered oxygen production levels

• Increased CO2

• Changed climate (radiation, temperature) and
  hydrologic cycle

• Loss of flora and fauna

• Increased soil erosion (i.e., global erosion
  rate of 25.4 billion tons of top soil per year)

• Increased effects of floods, especially coastal
  (e.g., 10x increase
• in catastrophic floods in Bangladesh)

• Landslides

• Cycle (vicious circle)

• deforestation ? soil erosion and loss of wood
  materials ? lowered productivity of soil and
  loss of wood source ? increased human needs ?
  enhanced deforestation

• e.g., 40-50 million trees removed in Haiti each
  year
• correlates with 7x increase in food aid over
  last 20 years

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• Global warming

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The balance of evidence suggests that there is a
discernible human influence on global climate '
Intergovernmental Panel on Climate Change (United
Nations), Second Assessment Report, 1996
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There is new and stronger evidence that most of
the warming observed overthe last 50 years is
attributable to human activity'
Intergovernmental Panel on Climate Change (United
Nations), Third Assessment Report, 2001
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Most of the observed increase in globally
averaged temperatures since the mid-20th century
is verylikely due to the observed increase in
anthropogenic greenhouse gas concentrations
Intergovernmental Panel on Climate Change (United
Nations), Fourth Assessment Report, 2007
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Discovery of the Greenhouse Effect
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GREENHOUSE EFFECT?
Glass allows visible radiation to pass through
the glass which absorbs thermal radiation and
re-emits some of it back into the greenhouse ---
like a radiation blanket.
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Heat Transfer --- Convection

• Less dense warm air moves upward and more dense
  cold air moves downward.
• Convection is the dominant process for
  transferring heat in the troposphere.

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The distribution of temperature in a convective
atmos.(red line). The green line shows how the
temperature increases when the amount of CO2
present in atmos. is increased (in the diagram
the difference between the lines is exaggerated).
Also shown for the two cases are the average
levels from which thermal radiation leaving the
atmosphere originates (about 6km for the
unperturbed atmosphere).
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Radiation is emitted out to space by these gases
from level somewhere near the top of the atmos.
typically from between 5 and 10km high. Here,
temperature is much colder -30 50C or so colder
than at the surface. gt emitting less radiation
to space. So absorb radiation emitted from the
earth surface but then to emit much less
radiation out to space.
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Component of the radiation (in watts per square
meter) which on average enter and leave the
earths atmos. and make up the radiation budget
for the atmosphere.
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The enhanced greenhouse effect
F ?T4 ? 5.67 x 10-8 W/m2/K4
average levels from which thermal radiation
leaving the atmosphere originates
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Blackbody rad. curves for Sun Earth
?max const./T Temp. T in K const. 2898 ?m
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Planetary energy balance

• Earth is at steady state
• Energy emitted by Earth
• Energy
  absorbed ..(1)
• E emitted (area of Earth) ? ? Te4
• 4? Re2 ? ? Te4
• (Te Earths effective rad. temp., Re Earths
  radius)
• E absorbed E intercepted - E reflected
• Solar E intercepted S ?Re2 (solar flux S)
• Solar E reflected AS ?Re2 (albedo A)
• E absorbed (1-A) S ?Re2
• (1) gt 4? Re2 ? ? Te4 (1-A) S ?Re2

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Magnitude of greenhouse effect

• ? Te4 (1-A) S/4
• Te (1-A) S/(4 ? )1/4 (i.e. fourth root)
• Te 255K -18C, very cold!
• Observ. mean surf. temp. Ts 288K 15C
• Earths atm. acts as greenhouse, trapping
  outgoing rad.
• Ts - Te ?Tg, the greenhouse effect
• ?Tg 33C

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Greenhouse effect of a 1-layer atm.

• Energy balance at Earths surface
• ?Ts4 (1-A)S/4 ?Te4 ..(1)

• Energy balance for atm.
• ?Ts4 2 ?Te4 .. (2)

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• Subst. (2) into (1)
• ?Te4 (1-A)S/4 ..(3) (same eq. as in last
  lec.)
• Divide (2) by ? take 4th root
• Ts 21/4 Te 1.19 Te
• For Te 255K, Ts 303K. (Observ. Ts 288K)
• ?Tg Ts - Te 48K,
• 15K higher than actual value.
• Overestimation atm. is not perfectly absorbing
  all IR rad. from Earths surface.

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• Weather forecasting also uses atm. GCMs.
  Assimilate observ. data into model. Advance model
  into future gt forecasts.
• Simpler 1-D (vertical direction)
  radiative-convective model (RCM)
• Doubling atm. CO2 gt 1.2C in ave.sfc.T
• Need to incorporate climate feedbacks
• water vapour feedback
• snow ice albedo feedback
• IR flux/Temp. feedback
• cloud feedback

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Water vapour feedback

• If Ts incr., more evap. gt more water vapour gt
  more greenhouse gas gt Ts incr.
• If Ts decr., water vap. condenses out gt less
  greenhouse gas gt Ts decr.
• Feedback factor f 2.
• From RCM ?T0 1.2C (without feedback)
• gt ?Teq f ?T0 2.4C.

()
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Snow ice albedo feedback

• If Ts incr. gt less snow ice gt decr. planetary
  albedo gt Ts incr.

()
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IR flux/Temp. feedback

• So far only ve feedbacks gt unstable.
• Neg. feedback If Ts incr. gt more IR rad. from
  Earths sfc. gt decr. Ts

(-)

• But this feedback loop can be overwhelmed if Ts
  is high lots of water vap. around
• gt water vap. blocks outgoing IR
• gt runaway greenhouse (e.g. Venus)

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Climatic effects of clouds

• Without clouds, Earths albedo drops from 0.3 to
  0.1.
• By reflecting solar rad., clouds cool Earth.
• But clouds absorb IR radiation from Earths
  surface (greenhouse effect) gt warms Earth.
• Cirrus clouds ice crystals let solar rad. thru,
  but absorbs IR rad. from Earths sfc.
• gt warm Earth
• Low level clouds (e.g. stratus) reflects solar
  rad. absorbs IR gt net cooling of Earth

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• IR rad. from clouds at ?T4
• High clouds has much lower T than low clouds
• gt high clouds radiate much less to space than
  low clouds.
• gt high clouds much stronger greenhouse effect.

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Uncertainties in cloud feedback

• Incr. Ts gt more evap. gt more clouds
• But clouds occur when air is ascending, not when
  air is descending. If area of ascending/descending
  air stays const.
• gt area of cloud cover const.
• High clouds or low clouds? High clouds warm
  while low clouds cool the Earth.
• GCMs resolution too coarse to resolve clouds gt
  need to parameterize (ie. approx.) clouds.
• GCM gt incr. Ts gt more cirrus clouds gt warming
  gt positive feedback.
• gt ?Teq 2 -5C for CO2 doubling

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Greenhouse Gases
Water Vapor Carbon Dioxide (CO2) CH4 methane,
N2O nitrous oxide...
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NATURAL GREENHOUSE EFFECT
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ENHANCED GREENHOUSE EFFECT
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• Water Vapor
• source evaporation from Earths surface
• location the lowest 5 km of the
  atmosphere
• residence time 10 days
• variation range 0.1 - 4
• roles in atmosphere source of moisture
  for
• cloud absorber of energy
  emitted by
• Earths surface greenhouse
  gas.

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Water Vapor

• Naturally occurring greenhouse gas, generally
  unaffected by humans.

Importance The Clausius-Clapeyron relationship
(shown below) suggests that warmer air can hold
more water vapor. As the planet warms due to the
greenhouse effect, more water vapor will change
global climate conditions.
By solving for water vapor (e), we can see that
temperature (T) increases the amount of water
vapor.
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• Carbon Dioxide (CO2)
• source plant and animal respiration, the decay
  of organic materials, and natural and
  anthropogenic (human-produced).
• Current concentration 380ppm (parts per
  million, i.e., 0.04) a global increase in
  recent decades.
• The increase in carbon dioxide (CO2) has
  contributed about 72 of the enhanced greenhouse
  effect to date, methane (CH4) about 21 and
  nitrous oxide (N2O) about 7.

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The Carbon Cycle

• There is a natural process by which carbon
  dioxide is cycled through the Earth's ecosystems
  and atmosphere.
• The blue arrows represent the natural processes
  by which living organisms emit and absorb carbon
  throughout their life and death (e.g.
  Respiration, photosynthesis, decomposition)?

The red arrows represent the anthropogenic flux
which is a scientific term for the human effect
on the carbon cycle, including industrialization
and fossil fuel burning.
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• carbon is exchanged between the biosphere,
  geosphere, hydrosphere, and atmosphere of the
  Earth.
• Four reservoirs of CO2 atmosphere, ocean,
  biosphere and sediments.
• Carbon cycle modeling. Models of the carbon
  cycle can be incorporated into global climate
  models, so that the interactive response of the
  oceans and biosphere on future CO2 levels can be
  modeled. Such models typically show that there
  is a positive feedback between temperature and
  CO2.

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• The land and ocean are large reservoirs to stock
  carbon than atmos. For example, the release of
  just 2 of the carbon stored in the oceans would
  double the amount of atmos. CO2.
• At the time scales which we concern, CO2 is not
  destroyed but redistributed among the various
  carbon reservoirs. E.g., about 50 of an increase
  in atmos. CO2 will be removed within 30 years, a
  further 30 within a few centuries, and the
  remaining 20 may remain in the atmos. for many
  thousands of years.

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The Human Footprint

• 5 of the world's population resides in the
  United States, creating ¼ of the total greenhouse
  gas emissions.
• For most people, their car is the main source of
  emissions. 22Lbs of CO2 is produced from every
  gallon of gas. Do the math
• Number of miles traveled by car each year __ ,
  divide by average miles per gallon __ gallons
  of gas, multiplied by 22 lbs CO2/gallon of gas
  __ pounds of CO2
• The 1997 Kyoto protocol called for all people to
  limit their carbon emissions to 5.4 tons, or
  about 11,000 lbs, per year.
• Some scientists believe that in order to reverse
  the damage caused by greenhouse gas emissions, we
  would need to reduce our individual emissions
  down to 5,000 lbs per year.

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Solving the Carbon Dilemma

• What are some things that you can do to reduce
  your carbon emissions?

• It's the act of consuming less that will
  ultimately make a difference.
• Energy-efficient, energy-conserving electronics,
  lightbulbs, hardware and other devices are
  available for almost anything. You can expect
  that energy-efficient products are meant to last
  longer and will save you money.
• Reduce your dependency on cars!

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Greenhouse gases

• Greenhouse gases (CH4 methane, N2O nitrous
  oxide)
• trap outgoing radiation from Earths surface
• Coal burning ? Sulfur dioxide (SO2) ? acid rain.
• SO2 ? Sulfate aerosol, reflects sunlight gt
  cooling.
• 1940-1970 cooling may be due to coal burning.
• Coal burning incr. CO2 (long-term warming) and
  incr. sulfate aerosol (short-term cooling)
  aerosol washed out by precip.

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Atmospheric CO2 concentrations--recent.

• Seasonal cycle of atmospheric CO2
• (Mauna Loa record)

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• Short-term variability

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Global mean surface temperatures have increased
0.5-1.0 F since the late 19th century The 20th
century's 10 warmest years all occurred in the
last 15 years of the century. Of these, 1998 was
the warmest year on record. The snow cover in the
Northern Hemisphere and floating ice in the
Arctic Ocean have decreased, sea level has risen
4-8 inches over the past century.

• Some facts of global changes
• (1) Global warming

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Atmospheric CO2 concentrations--past 1000 years.
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Short term climate change
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Holland in 1565 (Little Ice Age)
(Pieter Bruegel)
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• Cooling in 1940s-1960s gt fear of coming ice age!
• Volcanic eruptions gt drop in temp. for 3 years
  (e.g., Agung 1963)
• Viking colony on Greenland lost by early 1400s.
• Little Ice Age in late 1500s.

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Emitted millions of tons of sulfur dioxide and
ash particles.
El Chicon Mexico, 1982
Agung, Indonesia, 1963
Mount Pinatubo, Philippines, 1991
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London smog in 1952

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Red cross simulated global mean Tem. (62
simulations)black line mean of all
simulationsblue round observed global mean
Tem.
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Anthropogenic greenhouse warming

• Atm. CO2
• Keeling started measuring atm.CO2 in 1958 on
  Mauna Loa, Hawaii
• Seasonal cycle (forests absorb CO2 in summer
  release CO2 in winter) rising trend

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local temp. trends
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An increasing body of observations gives
a collective picture of a warming world and
other changes in the climate system

• Global mean surface temperature increase
• (NH, SH, land, ocean)
• Melting of glaciers, sea ice retreat and
  thinning
• Rise of sea levels
• Decrease in snow cover
• Decrease in duration of lake and river ice
• Increased water vapor, precipitation and
• intensity of precipitation over the NH
• Less extreme low temperatures, more
• extreme high temperatures

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Recent Range Shifts due to Warming
Species Affected Location Observed Changes

Arctic shrubs Alaska Expansion into shrub-free areas
39 butterfly spp. NA, Europe Northward shift up to 200 km in 27 yrs.
Lowland birds Costa Rica Advancing to higher elevations
12 bird species Britain 19 km northward average range extension
Red Arctic Fox Canada Red fox replacing Arctic fox
Treeline Europe, NZ Advancing to higher altitude
Plants invertebrates Antarctica Distribution changes
Zooplankton, fish invertebrates California, N. Atlantic Increasing abundance of warm water spp.
Walther et al., Ecological responses to recent
climate change, Nature 416389 (2002)
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Red Arctic Fox
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Modes of Climate Variation
Periodic variation
Periodic variation
Abrupt shift in climate state
Warming or cooling to new climate state
Changes in amplitude or frequency of climate
oscillations
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• The three serious problems
• The three modern global change problems
  discussed in this chapter-- global warming, ozone
  depletion, or loss of biodiversity

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• The ozone depletion is the serious problem
  because
• It causes the most immediate damage to our planet
  and its inhabitants
• It can cause skin cancer
• It occurs faster than global warming, because
  global temperatures only rise 1 degree in 100
  years so this is an insignificant amount compared
  to the decline in the total amount of ozone

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• The loss of biodiversity is the serious problem
  because
• There is potential for recovery for the other
  problems the ozone layer could recover within a
  few generations and greenhouse gas concentrations
  should return to normal within a few million
  years.
• The recovery rate for species following
  extinction is tens of millions of years.
• Once a species is gone, it is gone for good.
• It could cause an imbalance in the Earths
  ecosystem and economy.
• Deforestation also contributes to global warming.

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• Global warming is the serious problem because
• It affects the greatest number of people
• Migration of marine animals could result
• Rising sea level could result
• Cold climate species might die
• Ozone depletion and deforestation are both
  confined to particular areas whereas global
  warming is truly global