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The Evolving Science and Politics of Climate Change


'Global warming' is a misnomer because it implies some-thing gradual, ... zephyrs, blizzards, tornadoes, & typhoons. When climate changes, the patterns change. ... – PowerPoint PPT presentation

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Title: The Evolving Science and Politics of Climate Change

The Evolving Science and Politics of
Climate Change
  • John P. Holdren
  • Teresa John Heinz Professor of Environmental
  • John F. Kennedy School of Government
    Professor of
    Environmental Science Policy
  • Department of Earth Planetary Sciences
  • Director
  • Presentation at
    School of Public Policy, University of Maryland
    1 May 2007

Main messages
  • Global warming is a misnomer because it implies
    some-thing gradual, uniform, benign, none of
    which is true global climatic disruption is a
    more accurate description.
  • The disruption its impacts are growing more
    rapidly than was expected.
  • Dangerous anthropogenic interference can no
    longer be avoided. Goal must be to avoid
    catastrophic interference.
  • This is a big challenge because early large
    deflections from the business as usual
    emissions path are required.
  • There is no panacea, but much that can be done.
    Most important is putting a price on carbon
    dioxide emissions.
  • United States is (finally) near a political
    tipping point on climate-change policy.

What climate is what climate-change means
  • Climate is the pattern of weather, meaning
  • extremes, timing, spatial distribution of…
  • hot cold
  • cloudy clear
  • humid dry
  • drizzles downpours
  • snowfall, snowpack, snowmelt
  • zephyrs, blizzards, tornadoes, typhoons
  • When climate changes, the patterns change.
  • Global average temperature is just an index of
    the state of the global climate as expressed in
    these patterns. Small changes in the index ? big
    changes in the patterns.

What climate change puts at risk
  • Climate governs (so climate change affects)
  • availability of water
  • productivity of farms, forests, fisheries
  • prevalence of oppressive heat humidity
  • geography of disease
  • damages from storms, floods, droughts, wildfires
  • property losses from sea-level rise
  • expenditures on engineered environments
  • distribution abundance of species

The Earth is getting warmer on the average
Green bars show 95 confidence intervals
2005 was the hottest year on record the 13
hottest all occurred since 1990, 23 out of the 24
hottest since 1980.
J. Hansen et al., PNAS 103 14288-293 (26 Sept
But the heating is highly nonuniform…
Average T for 2001-2005 compared to 1951-80,
degrees C
and temperature is far from the whole story.
J. Hansen et al., PNAS 103 14288-293 ( 2006)
Evaporation precipitation are increasing
NCDC, 2000
Effect is not uniform most places getting
wetter, some getting drier.
Coastal glaciers are retreating
Muir Glacier, Alaska, 1941-2004
August 1941
August 2004
NSIDC/WDC for Glaciology, Boulder, compiler.
2002, updated 2006. Online glacier photograph
database. Boulder, CO National Snow and Ice
Data Center.
Mountain glaciers are retreating, too. Qori Kalis
Glacier, Peru
Permafrost is thawing Average ground temperature
near Fairbanks, Alaska, degrees C
Permafrost thaws when T 0C
ACIA 2004
Sea ice is shrinking
Extent of Arctic summer ice in 1979 (top
satellite image) and in 2003 (lower satellite
image). North Polar ice cap is sea ice -- its
floating and so does not change sea level when it
melts. But the reduced reflectivity when the ice
is replaced by water amplifies the warming effect
of greenhouse gases.
NASA photograph
Greenland is melting
Summer surface melting on Greenland, 1979-2002
ACIA, 2004
Greenland melting (continued)
2005 broke the 2002 record
Sea-level is rising
ACIA, 2004
1993-2003 30 mm 3.0 mm/yr compare 1910-1990
1.50.5 mm/yr.
Species are moving
Evidence for a human role the last 1000 years
Proxy temperature reconstructions 125-yr
thermometer record
National Research Council, 2006
Direction rate of temperature change switched
suddenly in 1800s
Quantifying human vs natural influences
  • The quantitative measure of an influence on
    global climate is called forcing, which refers
    to the change in the radiative energy balance of
    the planet produced by the influence over a
    stated period.
  • Forcings are measured in watts per square
    meter, averaged over the surface of the Earth.
  • A plus sign on the forcing denotes a warming
    influence, a minus sign a cooling influence.

Human versus natural influences on global climate
1750-2005 (forcings in watts / square meter)
  • Human emissions leading to increases in…
  • atmospheric carbon dioxide 1.7
  • methane, nitrous oxide, CFCs 1.0
  • net ozone (troposphere?, stratosphere?) 0.3
  • absorptive particles (soot) 0.3
  • reflective particles (sulfates, etc.) - 0.7
  • indirect (cloud forming) effect of particles -
  • Human land-use change increasing reflectivity -
  • Natural changes in sunlight reaching Earth
  • The warming influence of anthropogenic GHG and
    absorbing particles is 30x the warming influence
    of the estimated change in input from the Sun.

IPCC AR4, WG1 SPM, 2007
The human role CO2 build-up for the last 250
years tracks emissions from fossil fuels
Fossil-fuel contribution is confirmed by reduced
C-14 fraction in atmospheric CO2. Fossil fuels
provide 80 of civilizations energy today.
The human role Compared to natural changes over
the past 10,000 years, the spike in
concentrations of CO2 CH4 in the past 150 years
is extraordinary.
IPCC AR4, WG1 SPM, 2007
Human role Comparing the last 150 years to
450,000 years of natural change Time scale
expanded for last 150 years (right side of
diagram) Data are based on analysis of gas
bubbles trapped in Antarctic Greenland
ice. Last time Earth might have been as hot as
today was interglacial peak 6,000 years ago
last time it was definitely hotter was previous
interglacial peak 130,000 years ago.
Hansen, Clim. Change 68, 2005
Thousands of years before 1850
Calibrating the human role
  • Sensitivity of Earths climate to forcings is
    defined as the change in average surface
    temperature produced by a forcing of 1 watt per
    square meter.
  • Sensitivity is also sometimes expressed as the
    change in average surface temperature that would
    be produced by a doubling of CO2 from its
    pre-industrial concentration of 278 ppmv, which
    corresponds to a forcing of 3.7 W/m2.

Calibrating the human role (continued)
Ice-core record supports a sensitivity
of 0.75ºC per W/m2
1000s of years before the present
Observations are Antarctic temperature anomaly
(derived from ice-core dD) divided by 2 to give
global-average T change. Calculated T is based
on known forcings assuming sensitivity of 0.75C
per W/m2. From J. Hansen 2005.
The smoking gun Current computer model with
sensi- tivity 0.75ºC per W/m2, using best
estimates of natural human influences (A) as
input, reproduces almost perfectly the last 125
years of observed temperatures (B). Other
fingerprints of GHG influence on climate also
match observations.
Source Hansen et al., Science 308, 1431, 2005.
Computer models match observed ?T on all
IPCC AR4 WG1 SPM, 2007
Black lines are decadally averaged observations.
Blue bands are computer models with natural
forcings only. Pink bands are computer models
with human natural forcings.
Changes in climate are already causing harm
Major floods per decade, 1950-2000
Theres a consistent 50-year upward trend in
every region except Oceania.
Harm is already occurring (continued)
Major wildfires by decade, 1950-2000
The trend has been sharply upward everywhere.
Correlation of wildfire increases with
temperature is clear
Westerling et al., SCIENCE, 18 August 2006
This works in part through soil moisture
Running, Science, 18 August 2006
Harm is already occurring (continued) Total power
released by tropical cyclones (green) has
increased along with sea surface temperatures
Source Kerry Emanuel, MIT, http//
emanuel/anthro2.htm. SST anomaly (deg C) with
arbitrary vertical offset. PDI scaled by

Kerry Emanuel, MIT, 2006
Long-term warming of the Main Development
Region is consistent with climate model
historical simulations that include greenhouse
gas forcing…
GFDL CM2.1 Historical
Forcing Runs Using 5 Random Initial Conditions
Deg C
Source Knutson et al. (2005) J. of Climate,
accepted for publication.
Bleaching of coral reefs has been increasing with
sea surface temperature (SST) all over the
world. These results are from the Caribbean.
McWilliams et al., ECOLOGY, 86, 2055, 2005
Harm is already occurring (continued)
The Amazon is drying
This results from the reinforcing effects of
altered atmospheric circulation patterns linked
to global climate change and the drying influence
of deforestation itself.
Nepstad et al., Forest Ecology Management 154,
Harm is already occurring (continued) The East
Asia monsoon is weakening
Qi Ye, Tsinghua University, May 2006
The change is as predicted by Chinese climate
modelers. It has produced increased flooding in
the South of China and increased drought in the
Harm is already occurring (concluded) WHO
estimates climate change already causing 150,000
premature deaths/yr in 2000
Where will business as usual take us?
  • A middle of the road scenario (global)
  • 2000
    2050 2100

  • ------- ------- -------
  • Population, billions 6.1 9.5
  • Economy, trillion 2000 45 170
  • Energy, exajoules 450 1100
  • Fossil CO2, gigatons C 6.4 14.3

The climate implications of where were headed
The next 100
years compared to the last 400
Colored lines pre-2000 are proxy-based T
reconstructions by different groups. Gray band
2000-2100 shows range of scenarios for future
developed by Inter-governmental Panel on Climate
Change. Continuation of recent trends (middle of
band) leads by 2100 to temperatures not reached
since the Eocene (25-35 million years ago), when
sea level was 20-30 m higher.
Where were headed Heat waves
Extreme heat waves in Europe,
already 2X more frequent because of global
warming, will be normal in mid-range scenario
by 2050
Black lines are observed temps, smoothed
unsmoothed red, blue, green lines are Hadley
Centre simulations w natural anthropogenic
forcing yellow is natural only. Asterisk and
inset show 2003 heat wave that killed 35,000.
Stott et al., Nature 432 610-613 (2004)
Where were headed Agriculture in the tropics
Crop yields in tropics start dropping at local ?T
Easterling and Apps, 2005
Where were headed Temperate-zone agriculture
Temperate-zone crop yields start dropping at
local ?T 1-2C
Drops are more gradual than in tropics, but
still significant.
Easterling and Apps, 2005
Where were headed droughts
Drought projections for IPCCs A1B scenario
Percentage change in average duration of longest
dry period, 30-year average for 2071-2100
compared to that for 1961-1990.
Where were headed Oceans acidifying as well as
warming pH history and
business as usual projection
Red line is global annual average blue lines
show ocean-to-ocean and seasonal variation.
Surface ocean pH has already fallen by 0.1 pH
unit. Projected additional changes are likely to
have large impacts on corals and other ocean
organisms that make skeletons/ shells from
calcium carbonate.
Melting the Greenland and Antarctic Ice Sheets
would raise sea level up to 70 meters This would
probably take 1000s of years, but rates of 5 m
per century are possible.
7 m
GIS Greenland Ice Sheet WAIS West Antarctic
Ice Sheet EAIS East Antarctic Ice Sheet
12 m
70 m
Dr. Richard Alley, 2005
Courtesy Jeffrey Bielicki, Harvard U, 2006
The choices
  • Society has three options
  • Mitigation, which means measures to reduce the
    pace magnitude of the changes in global climate
    being caused by human activities.
  • Examples of mitigation include reducing
    emissions of GHG, enhancing sinks for these
    gases, and geoengineering to counteract the
    warming effects of GHG.
  • Adaptation, which means measures to reduce the
    adverse impacts on human well-being resulting
    from the changes in climate that do occur.
  • Examples of adaptation include changing
    agricultural practices, strengthening defenses
    against climate-related disease, and building
    more dams and dikes.
  • Suffering the adverse impacts that are not
    avoided by either mitigation or adaptation.

The choices (concluded)
  • Mitigation and adaptation are both essential.
  • Human-caused climate change is already occurring
    and is already dangerous.
  • Adaptation efforts are already taking place and
    must be expanded.
  • But adaptation becomes costlier and less
    effective as the magnitude of climate changes
  • The greater the amount of mitigation that can be
    achieved at affordable cost, the smaller the
    burdens placed on adaptation and the smaller the

Mitigation leverage societys greenhouse-gas
emissions in 2000
The fossil fuels responsible for the energy
emissions were still supplying 80 of
civilizations energy in 2005
Stern Review (Oct 2006)
Mitigation options
  • Reduce deforestation increase reforestation
  • Modify agricultural practices to reduce emissions
    of greenhouse gases build up soil carbon
  • Reduce emissions of greenhouse gases soot from
    the energy sector
  • Scrub greenhouse gases from the atmosphere
  • Geo-engineering to create cooling effects
    offsetting greenhouse heating

Emissions from energy are 65 of the problem,
above all CO2 from fossil-fuel combustion
  • The emissions arise from a 4-fold product…
  • C P x GDP / P x E / GDP x C / E
  • where C carbon content of emitted CO2
  • and the four contributing factors are
  • P population, persons
  • GDP / P economic activity per person, /pers
  • E / GDP energy intensity of economic activity,
  • C / E carbon intensity of energy supply, kg/GJ
  • For example, in the year 2000, the world figures
  • 6.1x109 pers x 7400/pers x 0.01 GJ/ x 14
  • 6.4x1012 kgC 6.4 billion tonnes C

Wheres the leverage for reductions in these?
  • Lower is better for lots of reasons 8 billion
    people in 2100 is preferable by far to 10
  • Reduced growth can be achieved by measures that
    are attractive in their own right (e.g.,
    education, opportunity, health care, reproductive
    rights for women).
  • This is not a lever that most people want to
    use, because higher is generally accepted to be
  • But were not getting rich as fast as we think
    if GDP growth comes at the expense of the
    environmental underpinnings of well-being.
  • Internalizing environmental costs of economic
    growth (including those of climate change) may
    slow that growth a bit...but not much.
  • Some lifestyle changes in industrialized
    countries could increase quality of life even
    though they reduced GDP.

Leverage against CO2 emissions (continued)
  • Getting more GDP out of less energy i.e.
    increasing energy efficiency has been a
    long-term trend.
  • It could be accelerated. It entails more
    efficient cars, trucks, planes, buildings,
    appliances, manufacturing processes. This
    opportunity offers the largest, cheapest, fastest
    leverage on carbon emissions.
  • This ratio too has been falling, but more slowly
    than energy intensity of GDP. Reducing it
    entails changing…
  • the mix of fossil non-fossil energy sources
    (most importantly more renewables and/or nuclear)
  • and/or the characteristics of fossil-fuel
    technologies (most importantly with carbon
    capture sequestration).

How much mitigation is needed?
  • The UN Framework Convention on Climate Change of
    1992 is the law of the land in 188 countries
    (including the United States).
  • It calls for
  • stabilization of greenhouse gas concentrations
    in the atmosphere at a level that would prevent
    dangerous anthropogenic interference with the
    climate system.
  • But there was no formal consensus in 1992 as to
    what constitutes dangerous anthropogenic
    interference or what level of GHG concentrations
    will produce it.

How much mitigation is needed? (continued)
  • Theres still no formal consensus, but its
    becoming clear that
  • the current level of anthropogenic interference
    is dangerous.
  • The world is already experiencing rising
    incidence of floods, droughts, wildfires, heat
    waves, coral bleaching, summer melting of sea ice
    thawing of permafrost, shrinkage of mountain
    glaciers, accelerating loss of Greenland and
    Antarctic ice, drying out of rainforests, and
    category 4 5 cyclones.
  • Tavg would rise another 0.6C even if GHG
    concentrations were stabilized today (thermal
    lag of oceans).

How much mitigation? (continued)
  • Under continuation of BAU in growth of world GDP
    use of fossil fuels, increase in global average
    surface T above its pre-industrial value (?Tavg)
    is likely to reach almost 2C by 2050, 3C by
    2100, and 4-5C by 2150.
  • The best current science indicates that…
  • ?Tavg 1.5C could mean the end of coral reefs
  • ?Tavg 2C could mean catastrophic melting of
    Greenland Antarctic ice, producing rates of
    sea-level rise that could reach 3-5 meters per
  • ?Tavg 2.5C is likely to sharply reduce crop
    yields worldwide.

How hard must we pull the levers? Emission paths
for stabilizing CO2 concentrations to limit T
BAU (gt6C)
The path to avoid ?Tavg gt2C (gold) requires much
earlier, more drastic action than path to avoid
gt3C (green).
Stabilizing at 450-500 ppmv would be possible if
emissions were flat for 50 years, then declined.
Emissions proportional to economic growth
The green stabilization triangle represents the
emissions that should could be avoided by new
policies (a depiction due to Socolow Pacala).
Reduced carbon intensity of the baseline economy
Virtual Triangle
Currently projected path
Stabilization Triangle
Historical emissions
Flat path
Socolow Pacala, SCIENTIFIC AMERICAN, 9-06
The triangle can be filled by a portfolio of 7
Each wedge accounts for 1 GtC/yr in 2055
Methane Management
Energy Efficiency
Forests Soils
14 GtC/y
Fuel Displacement by Low-Carbon Electricity
Decarbonized Electricity
7 GtC/y
Decarbonized Fuels
This particular set of wedges is only
illustra-tive, not prescriptive.
There are more than 7 wedges to choose from
Here are 15 candidates.
Policy options for promoting mitigation
  • Measures to affect choices among available
  • analysis of and education about the options
  • correction of perverse incentives
  • lowering bureaucratic barriers
  • financing for targeted options
  • subsidies for targeted options
  • emission cap trade programs
  • taxes on carbon or energy
  • performance portfolio standards
  • Measures to improve mix of available technologies
  • improving capabilities for RDD
  • encouraging RDD with tax policy other policies
  • funding the conduct of RDD
  • promoting niche pre-commercial deployment
  • international transfer of resulting technologies

These are listed in order of increasing
intrusiveness political difficulty. But
combinations that dont include one of the last
three are almost certain to be insufficient.
Policy for getting there whats happened so far?
  • The Kyoto Protocol
  • a landmark as a negotiated global commitment
  • but limited in time frame, reductions required,
  • The EU carbon trading system
  • started January 2005, embracing 12,000
    installations accounting for 1/2 of EU carbon
  • C trading price reached 100/tC, but then fell
    because of weak targets a glut of cheap ways to
    reach them
  • United States
  • didnt ratify Kyoto federal climate policy
    consists of modest voluntary targets, tax
    incentives, and rhetoric about RD.

Increasing energy RD should be the easiest part,
but even that is not happening
US DOE energy RDD spending, FY1978-2008
Courtesy Kelly Gallagher, Kennedy School of
Govt, 2-13-07
The tipping point contributing factors
  • The drumbeat of new climate science
  • Peoples everyday experience (and news reports)
    of a changing climate Katrina.
  • Climate policies embraced by cities (300) and
    states (28)
  • Changing corporate attitudes publicity BP,
    Shell, GE, Dupont, Duke Energy, Exelon, Alcoa,
  • Bipartisan, multi-sectoral consensus reflected in
    high-profile reports (e.g., Energy Futures
    Coalition, National Commission on Energy Policy)
  • Shifting position of labor religious
  • 2005 sense of the Senate resolution
  • Al Gores film
  • 2006 shift in balance of power in Congress
  • 2007 IPCC reports

Corporate Greenhouse-Gas Reduction Commitments
and Results (as of 2005)
5 reduction
10 reduction Its made us more competitive
69 reduction 2 billion saved
10 reduction 650 million saved
Absolute cap
35 reduction 200 million saved
19 reduction
10 reduction
6 reduction
25 reduction 100 million saved
72 reduction
65 reduction 791 million saved
37 reduction
9 reduction
13 reduction
1 reduction 1.5 billion clean tech RD
25 reduction
17 reduction
After the tipping point What to do
  • Accelerate win-win technical and policy
  • those that bring economic, political, public
    health, or other environmental benefits besides
    climate-change mitigation
  • Put a price on carbon emissions so marketplace
    can work to find cheapest reductions
  • Ultimately price will probably need to reach
    100/tC to incenti-vize carbon capture
    sequestration from coal power plants.
  • Pursue a new global framework for mitigation and
    adaptation in the post-Kyoto period
  • This must include mandatory, economy-wide
    reductions in ratio of emissions to GDP
  • Increase investments in energy-technology
    research, development, demonstration
  • At least a quadrupling of public private
    funding worldwide is needed, along with more
    strategic coordinated management.
  • Expand international cooperation on deploying
    advanced energy technologies
  • Increased use of public-private partnerships
    will be key.

Climate change…the bottom line
  • Human-caused climate change is real.
  • Its already causing widespread harm and will
    cause more…sooner rather than later.
  • Tipping points into climatic catastrophe almost
    certainly await…but no one knows how soon.
  • This is not just an environmental problem. It is
    an economic problem, a political problem, an
    international security problem.
  • We are nearing a sociopolitical tipping point…in
    public policy-maker recognition of the size and
    pace of the problem.

The bottom line (concluded)
  • Climate change is not just our grandchildrens
    problem or our childrens problem. It is our
  • We and our predecessors caused it. We have the
    responsibility to address it.
  • If not addressed with adequate wit, wisdom, and
    resources, the disruption of global climate will
    thwart societal aspirations everywhere.
  • It will erode well-being where it now exists.
  • It will prevent the attainment of well-being
    everywhere else.
  • It will undermine any prospect for international
    peace and stability.
  • The costs of addressing it will be far less than
    the costs of ignoring it.
  • The countries and companies that take the lead
    in turning challenge to opportunity cost to
    benefit will help themselves and help us all.

Some key references
  • National Commission on Energy Policy, Ending the
    Energy Stalemate A Bipartisan Strategy to Meet
    Americas Energy Challenges, December 2004
  • John P. Holdren, The energy innovation
    imperative, Innovations Technology/
    Globalization/Governance, Vol. 1, No. 2, Spring
    2006 http//
  • Intergovernmental Panel on Climate Change,
    Climate Change 2007 The Physical Science Basis.
    Summary for Policy Makers. February 2007.
  • UN Scientific Expert Group on Climate Change
    Sustainable Development, Confronting Climate
    Change Avoiding the Unmanageable and Managing
    the Unavoidable, United Nations Foundation,
    February 2007 http//
  • Intergovernmental Panel on Climate Change,
    Climate Change 2007 Climate Change Impacts,
    Adaptation, and Vulnerability, Summary for Policy
    Makers. April 2007. http//

Addendum Excerpts from the 4th Assessment of the
Intergovernmental Panel on Climate Change
  • Working Group I
    The Scientific Basis
    Summary for Policymakers
  • released 2 February 2007

Excerpts on causes consequences to date
  • Global atmospheric concentrations of carbon
    dioxide, methane and nitrous oxide have increased
    markedly as a result of human activities since
    1750 and now far exceed pre-industrial values
    determined from ice cores spanning many thousands
    of years. The global increases in carbon dioxide
    concentration are due primarily to fossil fuel
    use and land-use change, while those of methane
    and nitrous oxide are primarily due to
    agriculture. (p 2)
  • The combined radiative forcing due to increases
    in carbon dioxide, methane, and nitrous oxide is
    2.30 W/m2 (2.07 to 2.53), and its rate of
    increase during the industrial era is very likely
    to have been unprecedented in more than 10,000
    years. (p 3)

Causes consequences to date (continued)
  • Changes in solar irradiance since 1750 are
    estimated to cause a radiative forcing of 0.12
    W/m2 (0.06 to 0.30), which is less than half
    the estimate given in the Third Assessment
    Report. (p 3)
  • At continental, regional, and ocean-basin
    scales, numer-ous long-term changes in climate
    have been observed. These include changes in
    Arctic temperatures and ice, widespread changes
    in precipitation amounts, ocean salinity, wind
    patterns, and aspects of extreme weather
    including droughts, heavy precipitation, heat
    waves, and the intensity of tropical cyclones.
    (p 4)
  • There is observational evidence for an increase
    of intense tropical cyclone activity in the North
    Atlantic since about 1970, correlated with
    increases of tropical sea surface temperatures.
    (p 6)

IPCC scenarios for 21st century ?T (ºC) compared
to 1980-99
Recent future trends in warming-related
IPCC 4th Assessment, Figure SPM-1, Feb 2007
IPCC definitions of confidence likelihood
Excerpts on expected future changes
  • It is very likely that hot extremes, heat waves,
    and heavy precipitation events will continue to
    become more frequent. (p 12)
  • Based on a range of models, it is likely that
    future tropical cyclones (typhoons and
    hurricanes) will become more intense, with larger
    peak wind speeds and more heavy precipitation
    associated with ongoing increases of tropical
    sea-surface temperatures. (p 12)
  • Projections based on SRES scenarios give
    reductions in average global surface ocean pH of
    between 0.14 and 0.35 units over the 21st
    century, adding to the present decrease of 0.1
    units since pre-industrial times. (p 12)

Excerpts on future changes (continued)
  • Both past and future anthropogenic carbon
    dioxide emissions will continue to contribute to
    warming and sea level rise for more than a
    millennium, due to the timescales required for
    removal of this gas from the atmosphere. (p 13)

End of excerpts from Working Group I Summary for
Policymakers, IPCC Fourth
Assessment, 2 February
Excerpts from Working Group II Impacts,
Adaptation, and Vulnerability Summary for Policy
Makers released 6 April 2007
Excerpts on observed impacts
  • Observational evidence from all continents and
    most oceans shows that many natural systems are
    being affected by regional climate changes,
    particularly temperature increases. (p 1)
  • Based on growing evidence, there is high
    confi-dence that the following effects on
    hydrological systems are occurring
  • increased run-off and earlier spring peak
    discharge in many glacier- and snow-fed rivers
  • warming of lakes and rivers in many regions, with
    effects on thermal structure and water quality.
    (p 2 )

Observed impacts (continued)
  • There is very high confidence, based on more
    evidence from a wider range of species, that
    recent warming is strongly affecting terrestrial
    biological systems, including such changes as
  • earlier timing of spring events, such as
    leaf-unfolding, bird migration and egg-laying
  • poleward and upward shifts in ranges in plant and
    animal species. (p 2)
  • There is high confidence, based on substantial
    new evidence, that observed changes in marine and
    freshwater biological systems are associated with
    rising water temperatures, as well as related
    changes in ice cover, salinity, oxygen levels,
    and circulation. (p 2)

Observed impacts (continued)
  • Of the more than 29,000 observational data
    series, from 75 studies, that show significant
    change in many physical and biological systems,
    more than 89 are consistent with the direction
    of change expected as a response to warming. (p
  • A global synthesis of studies in this Assessment
    strongly demonstrates that the spatial agree-ment
    between regions of significant warming across the
    globe and the locations of significant observed
    changes in many systems consistent with warming
    is very unlikely to be due solely to natural
    variability of temperatures or natural
    variability of the systems. (p 2)

Excerpts on projected impacts
  • By mid-century, annual average river runoff and
    water availability are projected to increase by
    10-40 at high latitudes and in some wet tropical
    areas, and decrease by 10-30 over some dry
    regions at mid-latitudes and in the dry tropics.
    (p 5)
  • Drought-affected areas will likely increase in
    extent. Heavy precipitation events, which are
    very likely to increase in frequency, will
    augment flood risk. (p 5)
  • In the course of the century, water supplies
    stored in glaciers and snow cover are projected
    to decline, reducing water availability in
    regions supplied by meltwater from major mountain
    ranges, where more than one-sixth of the world
    population currently lives. (p 5)

Projected impacts (continued)
  • The resilience of many ecosystems is likely to
    be exceeded this century by an unprecedented
    combination of climate change, associated
    disturbances (e.g., flooding, drought, wildfire,
    insects, ocean acidification), and other global
    change drivers (e.g., land use change, pollution,
    overexploitation of resources). (p 5)
  • Approximately 20-30 of plant and animal species
    assessed so far are likely to be at increased
    risk of extinction if increases in global average
    temperature exceed 1.5-2.5ºC. (p 6)
  • The progressive acidification of oceans due to
    increasing atmospheric carbon dioxide is expected
    to have negative impacts on marine shell forming
    organisms (e.g., corals) and their dependent
    species. (p 6)

Projected impacts (continued)
  • Crop productivity is projected to increase
    slightly at mid- to high latitudes for local mean
    temperature increases of up to 1-3C depending on
    the crop, and then decrease beyond that in some
    regions. (p 6)
  • At lower latitudes, especially seasonally dry
    and tropical regions, crop productivity is
    projected to decrease for even small local
    temperature increases (1-2C), which would
    increase risk of hunger. (p 6)
  • Regional changes in the distribution and
    production of particular fish species are
    expected due to continued warming, with adverse
    effects projected for aquaculture and fisheries.
    (p 6)

Projected impacts (continued)
  • Coasts are projected to be exposed to increasing
    risks, including coastal erosion, due to climate
    change and sea-level rise. The effect will be
    exacerbated by increasing human-induced pressures
    on coastal areas. (p 6)
  • Projected climate change-related exposures are
    likely to affect the health status of millions of
    people, particularly those with low adaptive
    capacity, through (p 7)
  • increases in malnutrition and consequent
    disorders, with implications for child growth and
  • increased deaths, disease and injury due to heat
    waves, floods, storms, fires and droughts
  • the increased burden of diarrhoeal disease
  • the increased frequency of cardio-respiratory
    diseases due to higher concentrations of ground
    level ozone related to climate change and,
  • the altered spatial distribution of some
    infectious disease vectors.

Projected impacts (concluded)
  • Very large sea-level rises that would result
    from widespread deglaciation of Greenland and
    West Antarctic ice sheets imply major changes in
    coastlines and ecosystems, and inundation of
    low-lying areas, with greatest effects in river
    deltas. Relocating populations, economic
    activity, and infrastructure would be costly and
    challenging. There is medium confidence that at
    least partial deglaciation of the Greenland ice
    sheet, and possibly the West Antarctic ice sheet,
    would occur over a period of time ranging from
    centuries to millennia for a global average
    temperature increase of 1-4C (relative to
    1990-2000), causing a contribution to sea level
    rise of 4-6 m or more. (p 8)

Summary of projected impacts versus T increase
above 1980-1999
Excerpts on adaptation
  • Adaptation will be necessary to address impacts
    resulting from the warming which is already
    unavoidable due to past emissions. (p 17)
  • A wide array of adaptation options is available,
    but more extensive adaptation than is currently
    occurring is required to reduce vulnerability to
    future climate change. (p 17)
  • Adaptation alone is not expected to cope with
    all the projected effects of climate change, and
    especially not over the long run as most impacts
    increase in magnitude. (p 17)

End of excerpts from Working Group II Summary for
Policymakers, IPCC Fourth
Assessment, 6 April 2007