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Global Climate Change
Impacts and Trends
 Temperature rise
 Precipitation
 Sea Level Rise
 Changing Habitats
International Panel on Climate
Change
 The International Panel on
Climate Change (IPCC)
produces the main reports
on climate change
 They are a scientific
intergovernmental body set
up by the World
Meteorological Organization
(WMO) and by the United
Nations Environment
Programme since 1988.
IPCC
 The IPCC process involves
hundreds of scientists from
about 140 countries, a
variety of fields, and a range
of views.
 Their function is to assess
the latest peer-reviewed
literature, compare different
computer model results from
various sources, and to
achieve consensus about
where the weight of the
evidence points and where
uncertainties lie.
IPCC
 The IPCC has documented observed trends in
 Surface temperature
 Precipitation patterns
 Snow and ice cover
 Sea levels
 Storm intensity patterns
IPCC: 2007 Conclusions
 Based on the evidence
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accumulated over the
last 40 years, these are
some of their main
conclusions.
The words in red were
very carefully chosen to
reflect quantifiable
estimates.
Very High Confidence
means the statement
has at least a 9 out of 10
chance of being correct
Very Likely means the
scientists are more than
90% sure
Likely means they are
more than 66% sure.
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Warming of the climate system is
unequivocal
Very high confidence that global
average net effect of human
activities since 1750 one of warming
Human-caused warming over last
30 years has likely had a visible
influence on many physical and
biological systems
Continued GHG emissions at or
above current rates would cause
further warming and induce many
changes in the global climate
system during the 21st century that
would very likely be larger than
those observed during the 20th
century.”
8
2007 IPCC
 Average surface temperatures on Earth increased by
an estimated 0.74oC in the past 100 years
 In the next 20 years, the prediction is an estimated
increase of 0.4oC
 Every degree C is equal to about 100 miles of latitude.
 Rising temperature means rising AC usage, which
means rising CO2 consumption, accelerating the
greenhouse effect

This is a positive feedback loop
Projected Temperature Increases
 This map shows projected increases in surface temperature for the
decade 2090-2099, relative to temperatures in 1980-1999.
 Land masses will warm more than oceans, and the Arctic will warm the
most, up to 7.5oC
 This map was generated using an emission scenario that is intermediate
in its assumptions, involving an average global temperature rise of 2.8oC
by 2100.
Data from Intergovernmental Panel on Climate Change. 2007. Fourth assessment report.
Changes in Precipitation
 Changing Patterns of rainfall/drought
 Overall increase at high altitudes
 Overall decrease at low and middle altitudes
 Worsening water shortage
 Extreme Precipitation events
 Droughts
 Storms - flooding
 Snowfall
 Hurricanes

In a warmer world, more hurricanes, longer
season, and more powerful storms
Effects on Precipitation
 This map shows projected changes in June-August precipitation for the
decade 2090-2099, relative to precipitation levels in 1980-1999.
 Browner shades indicate less precipitation, and bluer shades indicate more
precipitation. White indicates areas for which models could not agree.
 This map was generated using an emission scenario that is intermediate in
its assumptions, involving an average global temperature rise of 2.8oC by
2100
Data from Intergovernmental Panel on Climate Change. 2007. Fourth assessment report.
Effects on Precipitation
 More water vapor held by a warmer atmosphere also leads to
heavier rains and more snowfall. Intense precipitation over the
U.S. has increased 20% over the last century.
Effects on Precipitation
 But as storm tracks shift, it can also mean some areas get drier.
A 2004 study by the National Center for Atmospheric Research
found that the percentage of Earth’s land experiencing serious
drought had more than doubled since the 1970s.
Effects: Snow and Ice
 Snow and ice are melting at rates unseen for thousands of
years.
 In Glacier National Park, for example, there were 150 glaciers
in 1850. Today, there are 26.
1900
Grinnell Glacier, Glacier National Park
2008
Impacts: Snow and Ice
1938
2005
Grinnell Glacier, Glacier National Park
Effects: Snow and Ice
 Mountain glaciers
around the world
are retreating
 Glaciers in East
Africa, including
those on Mount
Kilimanjaro, have
been receding
since 1880.
Arctic Ice and Greenland
 Sea ice is dwindling
especially in the Northern
Hemisphere.
 Satellites have seen average
Arctic sea ice shrink by 2.7%
per decade from 1978 to
2006, with faster melting in
summer.
Arctic Ice and Greenland
 Permafrost is thawing
 Arctic Ice adds 0 to sea level rise

Ice floats, and displaces its weight, hence volume will remain constant
Antarctica
 Coastal Ice shelves are disintegrating
Impacts: Snow and Ice
 Albedo
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Snow and ice reflect the
sun’s energy back to space.
The white cover reduces
evaporation of water into the
atmosphere where it acts as
a greenhouse gas.
The dark ground absorbs
more heat.
This is a positive
feedback loop
Impacts: Snow and Ice
 Sea Ice Albedo effect -
positive feedback
 Exposed water is dark
and absorbs more energy
from the sun. The
temperature of the ocean
increases, leading to sea
ice melting fast.
 As more of the ocean
becomes ice free, more
sunlight is absorbed,
leading to further
temperature increases
and further melting of the
sea ice.
Sea Level Rise
 Data from tide gauges
(black line) and
satellite observations
(red line) show that
global average sea
level has risen about
17 cm during the 20th
century
 Gray shaded area
indicates range of
uncertainty. Thermal
expansion of water
accounts for most sealevel rise.
Data from Intergovernmental Panel on Climate Change. 2007.
Fourth assessment report.
Thermal Expansion of Water
 Water molecules get larger as they get
warmer.
 Sea levels rise about 1 cm per 0.1° C
 Hence due to thermal expansion, the sea
level has risen about 10 cm since 1900, with
a global mean sea level temp rise of about
1°C
 Thus sea level may rise by 15-45 cm due to
thermal expansion
Sea Level Rise
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7-23 inches by the end of the
century (IPCC)
2 ft: U.S. would lose 10,000
square miles
Increases erosion, loss of
wetlands, freshwater supplies
Coastal populations become
even more vulnerable to
storm surge and flooding.
Half of the world’s population
lives near coasts, sea-level
rise is a serious concern.
53% in the USA.
Sea Level Rise
 If all of the Earth’s ice and
snow were to melt, the
ocean would rise by about
80 meters (250 feet).
 At the present rate, the
oceans will rise between
18 to 75 cm during this
century, most of the
Maldives islands and their
coral reefs will be flooded.
Sea Level Rise
 The Polar Bear is the first animal to be
designated as an Endangered Species due
to global climate change.
Changing Oceans
 A warming planet means
continuing changes in its
ecosystems.
 As the oceans absorb
more carbon dioxide, the
chemistry of the ocean
changes, putting many sea
creatures at risk.
 Warming oceans lead to
coral reef bleaching
ultimately killing corals.
Ocean Acidification
 Higher CO2 means more
absorption by ocean water
means lower pH (carbonic acid)
 The IPCC projects that by 2100
the pH of the ocean will drop to
its lowest point in at least 20
million years.
 The potential loss of all shell-
building marine organisms,
including corals would be
devastating to the ecosystem
biodiversity.
Changing Terrestrial Habitats
 Changes in habitat
 Migration patterns
 Ecosystem changes
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Changes in species populations can ripple
through an ecosystem.
Effects on Ecosystems
Breeding periods change
Earlier blooming
Timing is off
Earlier insect hatching
Spring leaf out
Changing migration times
mosquitoes, birds, and insects are moving north in the Northern Hemisphere
Mismatched Timing
 Breeding success
threatened. Migratory
patterns no longer match the
growing season.
 Nesting is timed to insect
hatch for feeding fledglings.
Temp increase  earlier
spring leaf  earlier insect
hatch  insect numbers
peak is passed when eggs
hatch. Not enough food to
raise fledglings.
Many species will not be able to shift their
distribution fast enough to avoid extinction
Beech
 Possible effects of global
Future
range
Overlap
Present
range
(Data from Margaret B. Davis and Catherine Zabinski,
University of Minnesota)
warming on the geographic
range of beech trees based on
ecological evidence and
computer models.
 IF CO2 emissions doubled
between 1990 and 2050, beech
trees (now common throughout
the eastern United States) would
survive only in a greatly reduced
range in northern Maine and
southeastern Canada.
 Similarly, native sugar maples
would likely disappear in the
northeastern United States.
QUESTION: What difference
does it make if the range of
beech trees changes?
Why Should We Care?
 There will always be
natural variability, and
some places and some
years will be warmer or
cooler than average. In
general, however,
summers will get hotter,
not only because of higher
temperatures but also
because humidity will
increase. That means that
heat waves, like the one
that killed 35,000 people in
Europe in 2003, will
become more common.
U.K.: Train rails buckle
France: >14,000
deaths
Germany: Lowest river
levels this century
Switzerland: Melting
glaciers, avalanches
Portugal: Forest fires
2003 European Heat Wave
Why Should We Care?
 On the plus side,
winters will be
warmer in many
places, reducing
heating bills. And
the number of days
with frosts is likely
to decrease.
Water Availability
 Warmer temperatures
will also mean less snow
overall at certain
latitudes because more
will fall as rain, and the
snow that does fall will
melt faster. This affects
people living in areas
that depend on snow-fed
reservoirs for water.
Agriculture
 The IPCC projects increases of
5-20% in crop yields in the first
decades of this century, but the
crops will be more prone to
failure if climate variability
increases and precipitation
becomes less dependable.
 With higher temperatures comes
an increased potential for killing
freezes. This is because plants
start growing earlier, making
them more vulnerable to sudden
spring-time cold spells.
Agriculture
 Increased temperature
means a decreased
soil moisture unless
precipitation increases.
 Shifting agricultural
belts northward may
result in lower crop
production because of
poorer soils at the new
latitudes.
Disease and Infection
 As temperatures get milder,
mosquitoes, ticks, rodents,
and other disease carriers
will expand their range,
particularly in developing
countries.
 Here in the U.S., dengue
hemorrhagic fever, a
tropical, mosquito-borne
disease, hit for the first time
in modern times in 2005 in
the Lower Rio Grande
Valley.
Feedback loops
 Positive
 The change increases the process driving the change
 Polar ice pack melt
 As the sea ice gets thinner due to warming, the heat
exchange between warm sea water below the ice and cold
air above the ice speeds up, leading to faster melting of the
ice
 Negative
 The change produces an offsetting or equilibrating
process
 As temperature rises, evaporation increases, leading
to increased cloud formation, increasing albedo,
thereby lowering temperature
The U.S. emits about 6.4 billion metric
tons of greenhouse gases annually, 25%
of the world’s total.
6.4 billion metric tons
CO2/yr
These greenhouse gases last a
long time…
Carbon dioxide stays in the
atmosphere for approximately
100 years, methane lasts about
12 years. Other greenhouse
gases last even longer.
Warming begets more warming…
As these gases continue to raise surface
temperatures, they trigger the release of
even greater quantities of carbon dioxide
and methane that are currently trapped in
frozen Arctic permafrost and tundra soils,
further increasing temperatures.
A feedback mechanism ensues…
…potentially causing “runaway global warming”.
Carbon (109 metric tons)
Worldwide Carbon Emissions
8
7
6
5
Total
Liquid fuel
Solid fuel
Gas fuel
4
3
2
1
0
1750
1800
1850
1900
Year
1950
2000
Future Carbon Dioxide Levels
 Increasing CO2 emissions,
especially in China and
developing countries
 Likely to double within 150
years:
 Increased coal usage
 Increased natural gas
usage
 Decreased petroleum
usage (increased cost
and decreasing supply)
 China is now the leading
producer of CO2
How Sure Can We Be?
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What don’t we know?
Is there some critical piece
of the about climate
process we don’t
understand?
How and when will our
fossil fuel use change?
Will future, yet-to-bediscovered technologies
mitigate the problem?
How will changing
economics, global
population, and political
processes affect our ability
to tackle the problem?
Scientists Always Disagree
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Do we know enough about the drivers of climate to
know what causes change?
Are we underestimating the Earth system’s complexity?
Can models accurately simulate the complex climate
system?
Are there processes that will limit warming naturally?
On the other hand…
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Arctic sea ice melting faster than predicted.
Fossil fuel emissions exceeded most IPCC
projections.
 Are the assumptions about global energy use are
too optimistic?
 How quickly can developing countries reduce
GHG emissions?
 Calculations don’t include unexpected melting in
Greenland and Antarctica.
What Do Climate Scientists Really
Think?
 A survey conducted in
2007 by George Mason
University of U.S.
scientists who have
expertise in climate
science (not just a
scientific background)
 97% of the 489
respondents agreed that
“global average
temperatures have
increased” during the past
century.
 That’s up from 60% in
1991.
What Do Climate Scientists Really
Think?
 84% believe human
activities are causing the
warming, and only 5%
disagree.
 So the survey does
indicate the bulk of climate
scientists—those most
knowledgeable about the
field—now agree that
human activity contributes
to global warming.