Transcript Is the Sky Falling? A Christian Response to Ozone Depletion and

The Science of Climate Change
Dr. Douglas Allen
Dept. of Physics and Astronomy
Dordt College, Sioux Center, Iowa
April 19, 2007
Why is the Debate so Confusing?
Scientific Reasons
Philosophical Reasons
Climate Change Science
Indicators
Attribution
Projections
Consequences
Summary
Climate vs. Weather
Climate and weather are both described in terms of
physical properties of the atmosphere (temperature,
wind, pressure, humidity, precipitation, etc.)
Weather: refers to what is happening at any given time
(example: today’s high temperature is …)
Climate: refers to average weather over time and/or
geographic area. (example: the average temperature in
Iowa in 2005 was …)
“Climate change”: refers to a change in the average
weather over a certain geographic area.
“Global climate change”: refers to the change in the
average climate over the whole Earth.
Why is the Climate Change Debate so Confusing?
Scientific Reasons
Climate changes occur on long time-scales
 need long data records to discern trends
Climate change trends are smaller than normal
weather fluctuations  need good statistics
The atmosphere-ocean system is very complicated
 need computer models
Projections depend on uncertain human actions
 need to develop plausible scenarios
No one can be an expert on all areas of the debate
 need to decide who you will trust
Why is the Climate Change Debate so Confusing?
Philosophical Reasons
Worldviews influence how we filter scientific “data”.
“Virtually all the major disagreements between rival
theories in the sciences and in philosophy can be
ultimately traced to the differences between the religious
beliefs that guide them.” (R. Clouser, The Myth of
Religious Neutrality).
(Unwritten) rules of policy argument tend to be
more lenient than rules of scientific argument.
In policy argument, scientific “facts” may be poorly
presented in order to support a particular position.
Policy debate demands fast answers and can be
unsympathetic to scientific caution.
For further discussion see “The Science and Politics of Global Climate
Change: A Guide to the Debate,” by A. Dessler and E. Parson, 2006.
The Responsibility of the Scientist in the
Climate Change Debate
Provide accurate information about the likely magnitude,
causes, and projections of global climate change.
Be up front about all assumptions made.
Provide levels of uncertainty and statistical significance.
Use the peer-review process (an effective filter).
Provide results that are reproducible and refutable.
Provide quantitative results, not anecdotal evidence.
Reference claims to peer-reviewed publications.
Climate Change Research
• Information sources
– Observations of Climate Variables
• Direct: weather stations, ships, planes, buoys, satellites
• Indirect: tree rings, ice cores, corals, ocean sediments,
boreholes, glacier records, etc.
– Models that Simulate Past and Future Climate
• Global circulation models (GCMs)
• Regional climate models (RCMs)
• Coupled Atmosphere Ocean GCMs (AOGCMs)
• Dissemination of information
– Peer-reviewed journal articles
– Scientific Assessments
• Intergovernmental Panel on Climate Change (IPCC)
• Reports published in 1990, 1995, 2001, 2007
Is the Global Surface Temperature Rising?
Global Average
Temperature
Deviation
(1850-2005)
IPCC 2007 Figure
SPM-3
Increase of 0.74 oC or 1.3oF from 1906-2005
Warming is
larger over
land
Data from thermometers
Warming is
larger during
winter
The “Hockey Stick” Diagram
N. Hemisphere
Temperature
(1000-2000)
Data from tree rings, ice cores, and
other proxies
See Mann et al., Geophys. Res. Lett., 26 (6), 759-762, 1999.
Warming is
larger at high
latitudes
Other Indicators of 20th Century Warming
•
•
•
•
17 centimeter (±5) sea level rise
Decline in NH snow cover
Retreat of mountain glaciers
Global ocean heat content increase
since the late 1950’s (when we
started collecting good data)
• 10 -15% drop in Arctic spring and
summer sea-ice extent
• Warming of lower- and middle
troposphere
• Average atmospheric water vapor
content increase
From Climate Change
2007: The Physical
Science Basis, IPCC.
See IPCC Climate Change 2001: Working Group I Technical Summary
Potential Causes of 20th Century Warming
• Earth’s orbital variations  Large timescales
• Tectonic activity  Large timescales
• Volcanoes  Irregular, short-lived impact
• Internal variability  Magnitude of internal variability too
small to account for observed global-scale changes
• Solar variability  Solar variations play a role in climate,
but sun’s output has been relatively steady over last 25
years
• Human activities  Enhanced greenhouse effect
 Enhanced aerosols
See “The Science and Politics of Global Climate Change: A
Guide to the Debate,” by A. Dessler and E. Parson, 2006.
Total Solar Irradiance (1600-2000)
Maunder Minimum
~0.25% increase
(~3 W/m2)
Data from Lean (2000)
Little Ice Age
Data from Solanki and Krivova (2003)
Solar Variability
Solar Variations
• The Sun has a
0.06 W/m2 decrease (1980-2005)
0.54 W/m2 increase (1980-2005)
0.62 W/m2 increase (1980-2005)
0.10 W/m2 increase (1980-2005)
Potential Causes of 20th Century Warming
• Earth’s orbital variations  Large timescales
• Tectonic activity  Large timescales
• Volcanoes  Irregular, short-lived impact
• Internal variability  Magnitude of internal variability too
small to account for observed global-scale changes
• Solar variability  Solar variations play a role in climate,
but sun’s output has been relatively steady over last 25
years
• Human activities  Enhanced greenhouse effect
 Enhanced aerosols
See “The Science and Politics of Global Climate Change: A
Guide to the Debate,” by A. Dessler and E. Parson, 2006.
The Greenhouse Effect
Average temperature without greenhouse gasses = -6°C (21°F)
Average temperature with greenhouse gasses = +15°C (59°F)
Characteristics of Greenhouse Gases
Gas
Natural Sources
Anthropogenic Sources
Average Atmospheric
Residence Time
CO2 - Carbon
Dioxide
Respiration, plant
decomposition
Fossil fuel burning,
biomass burning (clearing
forests)
About 125 yrs.
(multiple time scales)
CH4 - Methane
Ruminant animals,
wetlands
Rice paddies, biomass
burning, landfills, natural
gas exploitation
12 yrs.
N2O - Nitrous Oxide
Natural soil
processes
Fertilizer app., fossil fuel
burning
120 yrs.
CFC’s –
Chloroflourocarbons
None
Aerosol prop.,
refrigerants, foam packing
65-130 yrs.
Trace gases tropospheric O3, CF4,
and others
Internal comb. engines,
aluminum production,
other
50,000 yrs. for CF4
Note: Water vapor is the dominant greenhouse gas, but water vapor
respond quickly to the atmospheric temperature and so is treated as a
part of the climate system that responds to external forcing.
Trends of Greenhouse Gas Concentrations
379 parts per
million in 2005
CO2 has risen by 35 %
280 parts
per million
CH4 has risen by 148 %
N2O has risen by 18 %
Correlation vs. Attribution
Carbon dioxide increase
appears to correlate well with
recent increase in temperature.
But a correlation alone doesn’t
necessarily indicate cause and
effect. [Examples]
In order to attribute causal
relationship scientists
construct models to test the
relative effects of various
physical processes.
Attribution of Climate Change Using Models
• To establish cause-effect relationship, need to use computer models that
simulate the known “laws” of physics, chemistry, etc.
• Climate models are similar to weather models, but focus on large-scale,
long-term changes rather than short forecasts.
• Models attempt to reconstruct past climate as well as project future climate.
The global mean radiative forcing of the
climate system for 2005 relative to 1750
IPCC 4th Assessment Report Figure SPM-2
Simple Climate Model Results
Earth
Sun
Solar Energy
Absorbed by Earth
Earth
IR Energy
= Emitted by
Earth
(1 – A) E = σ T4
E = 343 W/m2 (Average Solar Flux at Earth)
A = 0.16 (Earth’s Albedo, without clouds)
T = 267° K = -6° C (Earth’s average temperature)
See “Global Warming:
The Complete Briefing”
by John Houghton
Temperature without GG = -6°C (21°F)
Temperature with GG = +15°C (59°F)
Doubling carbon dioxide (all else constant) should result in an increase of 1.2°C.
With feedbacks (water vapor, ice-albedo, clouds), expected increase of 2 to 4.5°C
GCM reconstructions of global average temperature (1860-2000)
Including
Solar +
Volcanic
Activity
Including
Greenhouse
Gas increases
Model
Observations
Including
All Factors
See Stott et al., Science, 290, 15 Dec. 2000, 2133-2137, 2000.
Model Projections of Global Average Temperature
Projection based on
IPCC B2 Scenario
See Stott et al., Science, 290, 15 Dec. 2000, 2133-2137, 2000.
Multiple Model Projections
Global Average Temperature
Average temperature
increase of 1.8 C over
70 years.
Global Average Precipitation
Models generally
predict increased
precipitation
Experiments with 1% per year increase in carbon dioxide.
Doubling of carbon dioxide would occur in year 70.
All 20 models show increased warming, and most models
show increased precipitation.
From Climate Change 2001: The Scientific Basis, IPCC.
Projected temperature and sea levels based
on various carbon emission scenarios
Global Average Temperature
Increase from 1.7 to
4.2°C (3 to 7.5°F)
Global Average Sea Level
Increase from
10 to 90 cm
From Climate Change 2001: The Scientific Basis, IPCC.
Projections from 4th Assessment Report (graphs not yet available):
Temperature increase of 1.1 – 6.4°C, Sea Level Rise of 18-59 cm
Likely Global Warming Consequences
Increasing GG Concentrations? Virtually certain
Rising Temperatures? Virtually certain
Melting ice? Virtually certain
Rising Sea Levels? Very likely
Eroding coastlines? Very likely
J. Knox, Living in a Globally Warmed World, Phi Kappa Phi Forum, Vol. 86, 11-16.
Possible Global Warming Consequences
Strengthening Hurricanes? The jury is out
Intensifying heat waves? Possible
Worsening droughts and floods? Possible
Invading tropical diseases? Possible
Proliferating tornadoes? Unlikely
J. Knox, Living in a Globally Warmed World, Phi Kappa Phi Forum, Vol. 86, 11-16.
Summary
 Climate is influenced by many complex factors, some of
which we understand well while others are poorly
understood.
 Observational evidence supports global average surface
warming of ~0.74°C, sea level rise of ~17 cm over the
last century, and widespread melting of snow and ice.
 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.
 Models project additional warming of 1.1 – 6.4°C and
sea level rise of 18 - 59 cm by end of the 21st century.
 Regional impacts are also likely, but specific projections
are more uncertain than large-scale projections.
Short List of Recommended Resources
• IPCC Assessment Reports
– www.ipcc.ch
• Web pages
– www.realclimate.org
• Books
– Global Warming: The Complete Briefing
• John Houghton
– The Science and Politics of Global Climate Change
• Andrew Dessler and Edward Parson
– Surface Temperature Reconstructions for the Last 2000 Years
• National Research Council, 2006
• Data
– World Data Center for Paleoclimatology
• www.ncdc.noaa.gov/paleo/data.html
Extras
Winter Temperature
Trends (1976-2000)
Summer Temperature
Trends (1976-2000)
IPCC TAR Fig 2.10
Jones et al. (2001)
Around 10 million
people in Bangladesh
live less than 1 meter
above sea level.
Milankovich Cycles
Quinn, T.R. et al. "A Three Million Year Integration of the Earth's
Orbit." The Astronomical Journal 101 pp. 2287-2305 (June 1991).
The global mean radiative forcing of the
climate system for 2005 relative to 1750
IPCC WGI Fourth Assessment Report Figure SPM-2
Geographic Distribution of Trends (1976 – 2000)
IPCC TAR Figure 2.9. Adapted from Jones, P.D., T.J. Osborn, K.R. Briffa, C.K. Folland, E.B.
Horton, L.V. Alexander, D.E. Parker and N.A. Rayner, 2001: Adjusting for sampling density in grid
box land and ocean surface temperature time series. J. Geophys. Res., 106, 3371-3380.
Atmospheric “Governing Equations”
dv
 p    F  2  v Conservation of momentum
dt

Conservation of mass
   ( v )
t
Equation of state
p  RT
dT
dp
Cp

Q
Conservation of energy
dt
dt
q
   ( vq )   ( E  C )
Conservation of moisture
t
dO 3
 S (O 3models
)
Climate
attempt to solve this system of equations
dt
numerically (i.e., with computers). Models attempt to
reconstruct past climate and predict the future climate.
Earth’s Atmosphere
Composition:
78% nitrogen
21% oxygen
other “trace” gases (water vapor,
carbon dioxide, ozone, methane,
etc.)
Density at surface: 1.275 kg/m3
Pressure at surface: 1 atm (14.7 lb/in2)
Troposphere (0-10 km)
Stratosphere (10-50 km)
Mesosphere (50-80 km)
Thermosphere (above 80 km)
Average Surface Temp (15°C, 59°F)
Earth’s Orbital Variations (Milankovitch Cycles)
Precession (23,000 year cycle)
Current Distance of Earth from Sun
January: Earth at 147 million km
July: Earth at 152 million km
Jan
Total Solar Irradiance at Top of
Earth’s Atmosphere
7% diff in TSI between Jan/July
Data from SORCE/TIM Mission:
July
http://lasp.colorado.edu/sorce
Earth’s Orbital Variations (Milankovitch Cycles)
Eccentricity (100,000 year cycle)
Obliquity (41,000 year cycle)
http://www.homepage.montana.edu/~geol445/hyperglac/time1/milankov.htm