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Introduction to the
Science of Global
Climate Change
In this slide show, you will learn the following:
I.
The Operations of the Greenhouse Effect and
the Carbon Cycle
II.
The Historical Accumulation of Greenhouse
Gases in the Atmosphere
III.
The Measurement of Global Warming Potential
IV. Some Recent Observations of the Changing
Climate
V.
Ocean Circulation and Land Changes
VI. Climate Modeling Examples
VII. Aerosol Emissions and their Uncertain Effects on
Climate Change
VIII. Confusions and Controversies Regarding
Climate Science
IX. Thinking about the Climate System As a Whole:
The Gaia Hypothesis
X.
The Twelve Tipping Points: Weaknesses in the
System
I.
The Operations of
the Greenhouse
Effect and the
Carbon Cycle
A. The Atmosphere and the
Greenhouse Effect
B. How the Greenhouse Effect
Works
C. Greenhouse Gases and the
Climate System
D. The Energy Balance in the
Climate System
E. The Carbon Cycle
F. Carbon Fluxes
The Atmosphere and
the Greenhouse Effect


The atmosphere, the thin layer
of gases that surrounds the
surface of the planet, serves
many important functions.
Chief among these is trapping
heat from the sun’s radiation
that ordinarily would reflect off
the Earth’s surface back into
space.
 The
atmosphere
must
trap
this solar radiation in order for Earth
to be warm enough to support life,
otherwise Earth would be as frigid as
the lifeless moon.

This heat-trapping capability of
the atmosphere scientists call the
“greenhouse effect.” The atmosphere
forms a sort of heat-protecting shield
keeping life flourishing on Earth and
allowing solar radiation to drive the
climate supporting that life.

The atmosphere thus acts like
the glass walls of the greenhouse,
trapping heat by stopping solar
radiation loss.
How the Greenhouse
Effect Works



The sun produces solar radiation that passes through
the atmospohere.
Some of that radiation is absorbed by the Earth’s
surface and warms it.
Some of that radiation is also reflected by the Earth’s
surface and trapped by greenhouse gas molecules in
the atmosphere---especially CO2 (carbon dioxide),
CH4 (methane), N2O (nitrous oxide and related
compounds), CFC’s (chloroflourocarbons from
industry) and H2O (water vapor).


Greenhouse Gases
and the Climate
System
Greenhouse gases
form a crucial aspect of the
climate system, and they interact with the other
components in complex ways to regulate the
Earth’s temperature.
Studying the interactions between these
components is critical for understanding the
functioning of the climate system.
The Energy Balance
of the Climate System
The Carbon Cycle
Source: NASA Earth Observatory. URL:
http://earthobservatory.nasa.gov/Library/CarbonCycle/carbon_cycle4.html
Carbon Fluxes (cont.)

Carbon Fluxes, or the rates of movement of carbon through
various components of the carbon cycle, can vary.
II. The Historical
Accumulation of Greenhouse
Gases in the Atmosphere
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
Greenhouse Gas Increases in the Atmosphere Over
the Last 2000 Years
CO2 Emissions Since the Mid-18th Century
Recent Measurements of CO2 Concentrations in the
Atmosphere
Methane Emissions Since the Mid-19th Century
What Activities Are Causing These Emissions?
Likelihood of Human Causes of Climate Change
How Have Long-term Temperature Trends Correlated
to Greenhouse Gas Concentrations?
More Recent Changes in Global Average
Temperature Since the Middle Ages
Changes in Global Average Temperature Since the
Mid-19th Century
Influence of Anthropogenic Emissions
What Are Some Future Scenarios for Global
Temperature Increases?
Greenhouse Gas Increases in the
Atmosphere Over the Last 2000 Years
 Concentrations of carbon dioxide (CO2), methane (CH4), and nitrous oxide
(NOx) in the atmosphere have increased markedly since 1750 because of human
activities; and they now far exceed pre-industrial values (determined from ice
cores spanning many thousands of years). The global increases in CO2
concentration are due primarily to fossil fuel use and land-use changes like
deforestation, while those of CH4 and NOx are primarily due to agriculture.
Source: IPCC WG1 Fourth Assessment Report, Chapter 2 Final Figures
CO2 Emissions Since The Mid-18th
Century
Recent Measurements of
CO2 Concentrations in the
Atmosphere
Note the steady rise in the atmospheric concentration of CO2 in parts per
million since measurements began in 1959.
Methane Emissions Since the
Mid-19th Century
Source: Stern, D.I., and R.K. Kaufmann. 1996. “Estimates of global
anthropogenic methane emissions 1860-1993.” Chemosphere 33: 159-176.
What Activities Are Causing These
Emissions (Combined CO2, CH4,
and N2O) and in What Proportion?
Source: 2007 IPCC Fourth Assessment Report, Summary for
Policymakers, Fig 2.1c, p. 5.
How Likely Is It That Humans
Have Caused These
Changes?---IPCC
Definition
 Most of the observed increase in globally averaged
temperatures since the mid-20th century is very likely due
to the observed increase in anthropogenic greenhouse gas
concentrations. Discernible human influences now extend
to other aspects of climate, including ocean warming,
continental-average temperatures, temperature extremes
and wind patterns.
Likelihood
Terminology
Likelihood of Occurrence
Virtually Certain
>99% probability
Extremely Likely
>95% probability
Very Likely*---the
likelihood that human
activity is driving climate
change
>90% probability
Likely
>66% probability
More Likely Than Not
>50% probability
About As Likely As Not
33 to 66% probability
Unlikely
<33% probability
Very Unlikely
<10% probability
Extremely Unlikely
<5% probability
Exceptionally Unlikely
<1% probability
Source: IPCC Report WG1 Assessment Report
How Have Long-term Temperature
Trends Correlated To Greenhouse
Gas Concentrations?
Correlations between greenhouse gas concentrations and
temperature trends have been extremely close for several hundred
thousands of years…
(BP=before present)
More Recent Changes in Global
Average Temperature Since the
Middle Ages
Source: Mann, M.E., et. al., “On Past Temperatures and Anomalous Late 20th
Century Warmth,” Eos, 84, 256-258, 2003. URL:
http://www.realclimate.org/index.php/archives/2004/12/temperaturevariations-in-pastcenturies-and-the-so-called-hockey-stick/
Changes in Global Average
Temperature Since the Mid-19th
Century
Source:
http://www.globalwarmingart.com/wiki/Image
:Instrumental_Temperature_Record.png
Figure 2a IPCC Report---Long records of past changes in atmospheric
composition provide the context for the influence of anthropogenic
emissions.
What Are Some Future
Scenarios for Global
Temperature Increases?
Source: NASA Earth Observatory; Adapted from IPCC 4AR.
III. The Measurement of
Global Warming Potential
How Much Do Different
Man-Made Greenhouse
Gases Contribute to
Global Warming?
Calculating GWP (Global
Warming Potential)
GWP values and
GWP time horizon
Lifetime
lifetimes from
20
100
500
- years
2007 IPCC AR4
years years years
Methane
12
72
25
7.6
Nitrous Oxide
114
310
298
153
HFC-23
270
1200 14800 12200
(hydrofluorocarbon)
HFC-134a
14
3830 1430
435
(hydrofluorocarbon)
Sulfur Hexafluoride
3200 16300 22800 32600
IV. Some Recent
Observations of the
Changing Climate
A. General Observations
B. Arctic Temperature Increases
C. Melting Summer Sea Ice in the
Arctic
D. Melting of the West Antarctic Ice
Sheet
E. Increased Tropical Cyclone
Intensity
F. Increasing Droughts and
Desertification
G. Anomalous Sea-Level Rises
General Observations of Recent
Climate Change
Type of Data
Area of Glaciers
Direction
of Change
Warming
Size of Change
Direct Surface Air Temp
Warming
Average temp increased 0.6C since
the beginning of the 20th century,
over half of this increase since
1980.
Sea-level Change
Warming
Sea Ice
Warming
Sea-level has risen 15cm since the
beginning of the 20th century,
much of that likely as a result of
thermal expansion (water
expands as it warms).
Area of Arctic sea ice in spring and
summer has decreased by 15% in
last 50 years; thickness
decreased by 40% over the same
time.
Ocean Temp
Warming
Top 300m of ocean has warmed
0.18C over the last 50 years.
Satellite Temp Measurements
Warming
Satellite instruments show
consistent warming of 0.06C0.26C per decade.
Receding on average for over
200 years, implying a 0.6warming
this century.
Source: Dressler, Andrew E. and Edward A. Parson. 2006. The Science and Politics of
Global Climate Change: A Guide to the Debate. Cambridge, UK: Cambridge University
Press. Adapted from a table on page 65.
Some Observations of Recent
Climate Change: Arctic Temps
Arctic Temperatures Are Increasing at Much
Faster Rates than the Global Average (0.33C
per decade since the 1980s according to
some of the latest estimates*)
Source: Haven, Kendall. “Greenland’s Ice Island
Alarm.” (August 28, 2007). NASA Earth
Observatory Study
Some Observations of Climate
Change: Melting Summer Sea Ice in
the Arctic
Reductions in the total coverage of Arctic sea ice
during the summer months---including a record
minimum ice coverage recorded in 2007.
Arctic SeaIce Coverage
in summer
1979….
…in
summer
2007.
Source: NASA Earth Observatory, 1979 and 2007.
Observations of Climate
Change: Melting of the West
Antarctic Ice Sheet
The collapse of the Larsen B ice sheet over a
period of one month threatens the land glaciers
of Antarctica
Source: NASA Earth System Science Data and Services (December 5,
2007 article about 2002 “Larsen B” ice sheet collapse)
Observations of Climate Change:
Increased strength of tropical cyclones and
hurricanes.
Wind Speeds: 185 mph+ , Central Pressure: 882 millibars (a record in the
Atlantic Ocean Basin)
More Effects from Global Climate
Change: Increasing Droughts and
Desertification
Source: “Drying Up and Flooding Out”, The Economist, March
12, 2007.
More Observations of Climate
Change: Anomalous Sea-Level
Rises
V. Ocean Current and Land
Changes and their Interaction
with Climate Change
A. Global Ocean Circulation
B. Uncertain Stability of the Future Flow
of the Great Ocean Conveyor Belt
C. The Ocean and Carbon
D. Decreasing Carbon Absorption
Capacity in Land and Oceans
E. Impacts of Changing Land-Use on
Climate
F. Climate Change and the
Transformation of Biome Regions
Global Ocean Circulation
Pattern
Uncertain Stability of the Future
Flow of the Great Ocean
Conveyor Belt
The Ocean and Carbon
•The increase in CO2 in the atmosphere will
increase the carbon in the ocean; the result
will be the acidification of the ocean.
Decrease in Carbon Absorption
Capacity in Land and Oceans
Changing Land-Use Will Impact
Its Ability to Absorb or Reflect
Sunlight
Climate Change and the Transformation of
Biome Regions
VI. Climate Modeling
Examples
A. Modeling Climate Change’s
Impacts
B. Sensitivity in Climate Models
1. What are the Components of a
Climate Model?
C. Modeling Future Climate
Change: The Potential Effects of
Policy on Future Temperature
Increases
D. Modeling Sea Level Rises
Modelling Climate Change’s
Impacts
Source: MIT Joint Program on the Science and Policy of Global Change, URL:
http://web.mit.edu/globalchange/www/if.html
Sensitivity in Climate Models
Modeling Climate Change:
Early Global Climate Models
and The Key Factors
Influencing Calculations
Source: “NOAA Celebrates 200 Years of Science, Service, and
Stewardship.” National Oceanic and Atmospheric Administration. May
22, 2008.
http://celebrating200years.noaa.gov/breakthroughs/climate_model/modeli
ng_schematic.html. Accessed August 19, 2008.
Modeling Future Climate: The
Potential Effects of Policy on
Future Temperature Increases
Modeling Sea Level Rises
Close-Up Photo of a Moulin
Flowing into a Hole in a Large
Greenland Glacier
VII. Aerosol Emissions and Their
Uncertain Effects on Climate
Change
Aerosol Effects
• Direct Effect: aerosols reflect or
absorb visible and ultra-violet radiation
• Indirect Effects: aerosols create more
and smaller cloud droplets which
• increase reflection
• suppress rainfall
• Semi-Direct Effect: absorbing
aerosols heat local air and cool the
surface which
• suppresses convection
• suppresses condensation
• evaporates clouds
Observed Effects of Aerosol
Emissions on Recent Climate
Changes: The Intriguing Case
Study of the Sahel
Source: Rachel Nowak, “African droughts ‘triggered by Western pollution’”, New
Scientist, June 12, 2002; URL: http://www.newscientist.com/article/dn2393-africandroughts-triggered-by-western-pollution.html.
Total Effect of Aerosol Pollution
on The Radiative Balance of the
Earth’s Atmosphere
The total effects of aerosol pollution on the radiative balance of the Earth’s
atmosphere are still being worked out, but climate scientists have come
up with a workable approximation…
Source: 2007 IPCC Report, Summary for Policymakers
The Interaction Between Climate Change
Impacts and Future Variables: A List
Impacts
• Climate Variables
• Rainfall
• Temperature
• Sea Level Rise
• Frequency and Strength of Severe
Storms
• CO2
•Vulnerable Systems
• Ecosystems
• Water Supply
• Food
• Forests
• Built Infrastructure
• Human Health
• Air and Water Pollution
VIII. Confusions and
Controversy Regarding
Climate Science
A. How Much of the Scientific
Community Believes That Man Is
Driving Climate Change?
1. How does the IPCC Organize Itself
and Prepare Reports? (2 slides)
2. Other Scientific Bodies Endorsing
the IPCC’s Consensus Position
How Much of the Scientific
Community Believes That
Man Is Driving Climate
Change?
 The most recent and
authoritative statement about
climate change has come from
the IPCC Report…. “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 levels
determined from ice cores
spanning many thousands of
years.”
How Is the IPCC
Organized?
• WMO and UNEP Member countries
provide the scientists
• Work Programme of the IPCC is
Determined at the Annual IPCC Plenary
• Work Organized Under Four Task
Forces
How Are IPCC Assessment
Reports Accepted for
Publication?
Other Scientific Bodies
Endorsing the Consensus
Position on Climate Change…
 National Oceanic and Atmospheric
Administration (NOAA)
• The U.S. Environmental Protection
Agency (EPA)
Other Prominent
Scientific Bodies Endorsing
the Consensus Position on
Climate Change (cont.)…
 NASA’s Goddard Institute for
Space Studies
• American Geophysical Union (AGU)
Other Prominent
Scientific Bodies Endorsing
the Consensus Position on
Climate Change (cont.)…
 American Institute of Physics (AIP)
• National Center for Atmospheric
Research (NCAR)
Other Prominent
Scientific Bodies Endorsing
the Consensus Position on
Climate Change (cont.)…
 American Meteorological Society (AMS)
• The Royal Society (UK)
Other Prominent
Scientific Bodies Endorsing the
Consensus Position on Climate
Change (cont.)…
 Canadian Meteorological and
Oceanographic Society (CMOS)
• 11 national academies of science sign a
joint statement entitled: “Joint science
academies’ statement: Global response to
climate change.”
VIII. Confusions and
Controversy Regarding
Climate Science
B. Was Greenland Ice-Free During the
Medieval Warm Period?
1. Many wonder if the current
evidence of global warming merely
represents natural cyclical warming
reminiscent of the “Medieval Warm
Period.”
2. Greenland was not ice-free in the
Medieval Warm Period, and the
Medieval Warm Period does not
refute anthropogenic climate change.
Greenland in the
Medieval Warm Period
Below is a map of likely Viking settlements in Greenland during the
Medieval Warm Period based upon archaeological evidence.
Populated area of Greenland today…
VIII. Confusions and
Controversy Regarding
Climate Science


Is the Sun Driving The Current Climate Change?
Answer: The Sun Is Important to The Workings of the Climate
System To Be Sure, But If Anything the Sun Should Be
Causing the Climate to Cool. A Closer Examination Reveals
Overwhelmingly That Anthropogenic Causes Far Outweigh the
Sun’s Virtually Negligible Contribution to Climate Change.
Solar Radiation
Versus Average
Global Temperature
Changes
Source: “Solar Variability.” Max Planck Institute for Solar System
Research. 2003. URL: <http://www.mps.mpg.de/en/projekte/sunclimate/>. Accessed 24 June 2008.
VIII. Confusions and
Controversy Regarding
Climate Science
 Climate Models Are Unreliable---Scientists
Cannot Accurately Predict Long-Term
Changes in Global Temperatures. After all,
the meteorologist on the nightly newscast
seems to get the next day’s forecast wrong
quite often. So, why should I believe the
findings of climate models?
 Answer: Using the models to “hindcast”
(work backwards) into the past to see how
well they could have predicted climate in
the past shows that climate models are
pretty effective at showing long-term
trends.
Are Climate Models
Reliable Predictors of
Temperature Changes?
Source: 2001 IPCC Report, Ch. 12, Figure 12.7,
page 710.
Question: Water Vapor Is
the Most Significant
Greenhouse Gas, So Why
Worry About CO2 Or
Methane?
 Answer: Water Vapor is a very significant
greenhouse gas, but the amount of water
vapor in the atmosphere (roughly 2-3% of
the composition of the atmosphere)
ultimately depends upon the temperature.
Such changes in temperature have been
observed as a result of humankind’s
emissions of greenhouse gases like carbon
dioxide from burning fossil fuels, clearing
forests for agriculture, and from methane in
the rearing of livestock like bovine cattle.
The Correlation Between
Water Vapor and
Temperature
 Water, as a chemical, has tremendous
heat-trapping capabilities as we saw in
discussing the ocean circulation in earlier
slides.
 In calculating a global annual mean energy
budget (see slide 7) for the effects of
incoming solar (shortwave) radiation and
reflected infrared (longwave) radiation that
both escapes into the atmosphere and
interacts with clouds, aerosols, and
greenhouse gases----water vapor’s
contribution to the global annual mean
energy budget is 75w/m-2 in that it traps
that amount of heat energy per square
meter over the course of an entire year.
CO2’s contribution is less----only 32w/m-2.
Increasing Water Vapor
in the Atmosphere: A
Positive Feedback Loop
Source URL: Bill Chameides. “The Water Vapor Falacy.” Climate
411 Blog. The Environmental Defense Fund. Posted Februrary
28, 2007. Accessed 28 July 2008.
http://environmentaldefenseblogs.org/climate411/2007/02/28/wate
r_vapor_fallacy/.
Conclusion: