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OC450: Climatic Extremes (Winter 2009)
• Profs: Paul Johnson and Paul Quay
• School of Oceanography
• Taught class for >10 years
• Time/Place: 205 OTB (M, W, Th, F at 11:30)
• Web Page:
http://courses.washington.edu/ocean450/
1
Adjusting Class Schedule Possibility
1. Keep class schedule as is (10 weeks, meeting 4x/week).
-Add special projects for students going on field trip.
2. Re-schedule the 40 lectures as a 8-week class, with 5
lectures a week (add extra class at 11:30 on Tues or
another time slot)
-Course finishes at end of Week 8 w/Final Exam.
3. Extend 2 lectures per week until ~12:50 pm (M, W or Th)
-Course finishes at end of Week 8 w/Final Exam
2
What do we want you to learn?
• What does the record of past climate change on
earth tell us about future climate change?
• What climate records are available to study past
climate change?
• What are the important processes of the earth’s
climate system that control climate?
• What are the major feedbacks in the earth’s
climate system?
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Course Components
• Syllabus
-Schedule of lecture topics, lecturer and corresponding chapters
in Textbook for each week
-Follow the textbook: Earth’s Climate: Past and Future by
W.F. Ruddiman (2001). Very readable. ~ 2 Chapters/week
• Lectures (M, W and F)
- Read textbook chapters ahead of time, if possible
- The figures used in lectures will be posted on the class web
page ahead of time. Bring to class.
4
Course Components
• Paper Discussions (~8 total, every Thursday)
-Papers distributed (posted on Web Page) a week
ahead.
-Three or so questions to answer in writing (turn in).
-Oral discussion of paper
-randomly pick ~3 students to lead discussion
-focus on key figures and questions
• Problem Sets (~8 total, due on Fridays)
- receive problem a week ahead
- quantitative examples of concepts discussed in
lectures
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Course Components
• Exams: Midterm and Final
-Midterm (Week 6) and Final (finals week)
-both descriptive and quantitative questions
• Grading
Problem Sets 25%
Paper Discussions/Questions 25%
Midterm 25%
Final 25%
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Climate
• Climate represents average environmental conditions
-primary characteristics: temperature, precipitation,
-other characteristics: greenhouse gas concentrations, sea
level, ice sheet extent, aridity, cloudiness, winds, ocean
currents
• Spatial and temporal scales of climate indicators
-large spatial scale: global, ocean basins, continental,
regional
-long time scales: millions years, millennial, century,
decadal, annual.
• Weather, in contrast, focuses on local spatial scales and
short term (daily or weekly) variations in atmospheric
conditions (temperatures, precipitation, winds)
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Climate System on Earth
Forcing
Feedbacks
Response
Anthropogenic
Changes
8
Past Climate Change
• What were the conditions on earth during previous
periods of extreme climate?
-e.g., temperature, precipitation, atmospheric CO2 and
CH4 levels, position of the continents, vegetation distribution, ice
sheet extent, etc.
• What processes affected climate in the past?
-e.g., weathering, ocean and atmospheric circulation, solar
insolation, photosynthesis, plate tectonics, ice sheets, etc.
• How important are the time scales of theses processes?
-e.g., the position of the continents change at a much
slower rate than the growth of ice sheets
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Climate Proxies
• A key part of reconstructing climate in the past is the
use of climate proxies.
• For climate studies, a proxy is a record that represents
the actual climate characteristic.
-e.g., use the oxygen isotope composition of ice in
Greenland and Antarctica ice sheets to reconstruct air
temperature record over the last 750,000 years
-e.g., use the oxygen isotope composition of
CaCO3 in deep sea sediments to reconstruct ice sheet
extent and ocean temperature
-e.g., use the distribution of continentally derived
minerals in deep sea sediments to reconstruct the presence
of icebergs in the N. Atlantic Ocean.
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Current and Future Climate Change
• Anthropogenic Impacts on Climate
- greenhouse gas concentrations in air (CO2, CH4, N2O)
- aerosol concentrations in air (impact on clouds)
• Natural Variations in Climate
- El Nino Events (every few years)
- Ice Age Transitions (every 100,000 years)
• Future Climate………The BIG question!
-How accurately can we predict future climate change?
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Importance of Climate and Climate Change
• Climate affects our quality of life
-e.g., food production, energy production and
consumption, water availability, environmental diversity.
• Climate will change in the future
-both natural variations and anthropogenic effects
-can society reduce the impact of climate change?
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Questions about Future Climate Change
• Scientific questions
- What can we learn about future climate change from past
climate change?
- How accurately can we separate current and future climate
change into natural and anthropogenic causes?
- Can we use advances in technology and engineering (e.g.
energy production) to significantly reduce climate change?
• Social/economic/political questions:
- Do we have the political and personal will to reduce
greenhouse gas emissions?
- Can we successfully adapt to climate change?
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Climate Change in the Pacific Northwest
• The Pacific NW is an excellent example of a region that
will be significantly impacted by climate change
-this region is affected by both natural and
anthropogenic causes of climate change
• El Nino and Pacific Decadal Oscillation are natural
oscillations in the atmosphere/ocean circulation scheme
that causes changes in climate of the Pacific NW
-affect temperature and precipitation rates in the
region
• UW’s Climate Impacts Group
http://www.cses.washington.edu/cig/
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Climate Change in the Pacific Northwest
• Region’s history and economy has evolved based on the
availability of water throughout the year
-water for hydroelectric power (cheap electricity)
-water for agriculture (irrigation in E. Washington)
-water for salmon (spawning in fall)
• How will global warming (predicted 3-4ºF over next 50
years) affect the Pacific NW’s water cycle?
-loss of snow pack
-reduced summer stream flow
• What will be the impact on hydroelectricity, irrigation,
salmon, forest fire frequency, recreation, and quality of life?15
Trends in Temperature and Snow Pack in
the Pacific Northwest during last 50-80 years
Pacific NW is warming and losing snow pack.
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Comparing
Impacts of
Natural and
Future Climate
Change in the
Pacific NW
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Predicted Columbia River Discharge
Changes over the next 50 years
Reduced snow pack changes the shape of the hydrograph.
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Climate Models Predict Climate Change
• What are climate models?
-mathematical representation of the earth’s climate system
(typically this includes atmosphere, land and oceans)
-climate models are essential for predicting future change
• How accurate are model predictions?
-policy makers want to know the likelihood or
probability of a climate change prediction
• How sensitive are local or regional climate
predictions to global conditions?
-e.g., how do predicted changes in the circulation of
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the equatorial Pacific Ocean affect climate in the Pac NW?
Simple Reservoir or Box Models
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General Circulation Models (GCMs)
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Observed
Temp
Model
Hindcasts
for
Validation
Model
Temp
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Climate System on Earth
Forcing
Feedbacks
Response
Anthropogenic CO2
How accurately can models simulate climate system?
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Components of Earth’s Climate System
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Response Times of the Earth’s Climate System
Plate Tectonics
10s-100’s x 106 yrs
Position of continents
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Response Time
Illustration
The magnitude and
time of temperature
response of the water
depends on:
-heating rate
-duration of heating
-size of reservoir
being heated
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Response vs Forcing
The size of the reservoir
relative to the magnitude
and frequency of the
forcing determines the
magnitude of change.
Generally, as the size of
the reservoir increases, the
response is smaller and
slower.
27
Reservoirs and Budgets
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Reservoir’s Heat Budget
- The rate of change of heat content of the reservoir depends on the
heat input and heat loss rates.
ΔHeat /Δtime = Heat Input Rate – Heat Loss Rate
- Units: Heat is in Joules
- Heating rate in Joules/s or Watts (1 Watt = 1 Joule/sec)
ΔHeat/Δtime = 0 when heat input rate equals heat loss rate and
temperature of reservoir doesn’t change (i.e., steady-state)
ΔHeat/Δtime > 0 when heat input rate exceeds heat loss rate and
temperature of reservoir increases
ΔHeat/Δtime < 0 when heat input rate less than heat loss rate and
temperature of reservoir decreases.
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Response Time
Illustration
Why does the rate of
temperature increase
slow down?
What does this imply
about the heat loss rate
versus time?
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Response versus Forcing
What does the heat loss vs time look like in the
situation where the max and min in the temperature of
the reservoir lags the max and min of the heat input ?
31
Oscillations in Earth’s Temperature
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Solar Insolation Reaching Earth (modern)
(mean = 342 W/m2)
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Seasonality of Solar Insolation
Insolation at high latitudes has much greater seasonality. 34
Seasonal Temperature Changes
Changes in the insolation rate has potentially biggest impact on
temperatures at high latitudes in N. Hemisphere. Why is this
region important in the earth’s heat budget?
35
Earth’s Modern Heat Budget
If the heat input from solar radiation exactly equaled the heat loss
from long wave radiation back to space then neither the heat
content nor the mean temperature on earth would change over time.
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Latitudinal Trends in Heating
Winds and ocean currents redistribute heat from tropics to
poles. Changes in currents or winds will change equator to
pole temperature gradients.
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Earth’s Heat Budget Terms
• At Steady-state: heat input equals heat output
ΔHeat/Δtime = Solar Insolation Input – Long Wave Back
Radiation Output
• Solar Insolation = 342 Watts/m2
- heat input expressed per unit surface area of earth
• Long Wave Radiation depends strongly on the temperature of
the radiator
LW Radiation = σ * T4 (ºK),
where σ = Stefan-Boltzman constant (5.67x10-8 W/m2/ºK4) and
Temperature (T) is in degrees Kelvin (ºK = ºC +273)
-a 10% increase in T (ºK) yields a 50% increase in heat loss
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Earth’s Heat Budget
ΔHeat/Δtime = Heat Input - Heat Output
ΔHeat/Δtime = I*(1 - α) – f * σ *T4,
-where I = solar insolation from sun, α = reflectivity of
incoming short wave radiation (~0.3) and f = transmissivity
(~0.6) of atmosphere to long wave radiation
-the reflectivity depends primarily on the amount of clouds
in the atmosphere and the proportion of ice, ocean and land
-the transmissivity of the atmosphere depends inversely on
the amount of greenhouse gases in the atmosphere
39
Using Earth’s Heat Budget to Calculate Temperature
• At steady-state, a heat balance implies ΔHeat/Δtime = 0
-ΔHeat/Δtime = I*(1 - α) – f * σ *T4,
-solve for T = [I*(1 - α) / (f * σ)]0.25
-Units = [(W/m2) / (W/m2 K4)]0.25 = ºK
• For the earth under present conditions:
α = 0.30 (30% of incoming SW insolation reflected
back into space)
f = 0.61 (61% of LW radiation reaches space)
• Under these conditions, the temperature of the earth needed to
maintain a steady-state balanced heat budget is 288 ºK (or 15ºC).
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Earth’s Heat Budget
• A steady-state temperature of 288 K or 15ºC
applies at earth’s surface.
• If there were no greenhouse gases in the earth’s
atmosphere (f = 1, rather than 0.61) the surface of
the earth would be 255 K or –18 º C.
• Like the surface of the moon
• Thus the natural level of greenhouse gases in the
Earth’s atmosphere keeps the surface of the earth
33ºC warmer than it would be in their absence.
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Earth versus Venus
• Venus Surface Temperature = 460ºC (vs 15ºC on earth)
• Closer to sun, but that’s not the reason.
• Venus’ atmosphere is 90x denser than earth’s and 96%
CO2. (f = 0.008) (Earth’s atmosphere is 0.03% CO2)
• Venus’ Heat Budget
ΔHeat/Δtime = I*(1 - α) – f * σ *T4
T (ºK) = [I*(1 - α) / (f * σ)]0.25 (at steady-state)
T = [645 W/m2*(1-0.8) / (0.008* 5.67x10-8 W/m2/ºK4)]0.25
T = 733 K or 460ºC
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Earth versus Venus
Atmospheric GHG composition is key factor causing
temperature difference on Venus vs Earth.
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Only Certain
Gases are
Greenhouse
Gases
Water Vapor (H2O)
Carbon Dioxide (CO2)
Methane (CH4)
Nitrous Oxide (N2O)
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Greenhouse Gas Heating in the Atmosphere
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Impact of Adding Greenhouse Gases
• Greenhouse gases (GHGs) reduce the transmissivity of LW
radiation through the atmosphere (decrease f) by increasing
the ability of air to adsorb long wave radiation.
• Thus by increasing the concentrations of GHGs in the
atmosphere, f decreases and the heat loss is reduced which
causes the earth to gain heat (warm).
ΔHeat/Δtime = Heat Inputs – Heat Outputs > 0
• At a lower value of f, the temperature of the earth’s surface
must increase in order to maintain a steady-state balanced
heat budget.
T (ºK) = [I*(1 - α) / (f * σ)]0.25
• Magnitude of human induced change in earth’s heat budget46
is small ~ 1.5 W/m2 since 1800s.
Predicting Warming Effect of GHGs
• The uncertainty in predicting the future warming
rate on earth is primarily a result of our
uncertainty in predicting the rate at which the
reflectivity (α) and transmissivity (f) will change.
– α depends on the amount (and type) of clouds, ice, etc.
– f depends on the future GHG composition of the earth’s
atmosphere (mainly depends on future CO2 input and
loss rates, which are uncertain)
– the change in solar insolation (I) can be accurately
predicted from the earth’s orbital characteristics
47
Feedbacks in the Earth’s Climate System
Complicate Temperature Predictions
Positive Feedback accelerates change. (as shown above)
Negative Feedback decelerates change.
48
Earth’s Carbon Cycle
• Importance: controls the concentration of CO2
(and CH4) in the atmosphere, which affects the
transmissivity (f) of the atmosphere.
• Variations in the earth’s carbon cycle in the past
have changed the concentration of CO2 (and CH4)
in the atmosphere and, thus, temperature of the
earth.
• Major Carbon Reservoirs: rocks, ocean, soils,
plants, atmosphere.
• Major Exchange Pathways: weathering,
volcanism, photosynthesis/respiration, atmosphereocean (air-sea) CO2 gas exchange.
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Earth’s Carbon Cycle
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Carbon Reservoirs on Earth
Reservoir Sizes
Units: Gigatons C or 1015
gms C or Pedagrams (Pg)
Reservoir Exchange Rates
Gigatons C/yr or Pg C/yr51
Residence (Turnover) Time for a Reservoir
• Residence Time = Reservoir Amount/ Input (or Output) Rate
For example: Vegetation on Earth
Residence Time = 610 Gtons C / 100 Gtons/yr
= 6.1 years
• This means that the average time a carbon atom spends in
plants on earth is 6.1 years.
-Does this seem reasonable?
• The residence or turnover time of a reservoir is a rough
estimate of that reservoir’s response time to a perturbation.
-the time it takes for the amount of material in the
reservoir to adjust to a change in the input (or output)
52
Long Term Controls on Atmospheric CO2
• Weathering, volcanism and sedimentation are processes that
exchange carbon between the atmosphere and rock
reservoir.
• These exchange rates are very slow (~0.2 Gtons C/yr)
• Thus the atmospheric CO2 response time to changes in rates
of weathering, sedimentation or volcanism is 1000s years.
τ = 600 Gtons C / 0.2 Gtons C/yr = 3000 years
• However, on geologic time scales (millions of years) this
atmospheric CO2 response time is extremely fast.
• Thus over the history of the earth, changes in weathering,
volcanism and sedimentation rates are effective ways to
change atmospheric CO2 levels.
53
Residence Time for CO2 in the Atmosphere
• CO2 Residence Time (τ) =Amount / Input (or Output)
τ = 600 GTons / (100 + 74.6 GTons/yr)
= 3.4 years
• This means that CO2 molecules remain in the
atmosphere for an average of 3.4 years before being either
photosynthesized by plants or adsorbed in the ocean
(weathering uptake rate of CO2 is much slower).
• This short residence time implies that the response of
the atmospheric CO2 pool will be quick to changes in CO2
exchange between the atmosphere, biosphere and ocean.
54
Atmosphere’s Carbon Reservoir Budget
ΔCarbon/Δtime = Inputs – Outputs (units: Gtons C /yr)
ΔCO2atm/Δt = - Photosynthesis + Respiration + Ocean CO2 Gas
Evasion – Ocean CO2 Gas Invasion Weathering
= -100 + (50+50) + 74.6 – 74 – 0.6 Gtons C/yr
= 0 Gtons C /yr
• In this situation, the atmosphere’s carbon (CO2) reservoir is at
steady-state, that is, the CO2 inputs equal the CO2 outputs and the
amount of CO2 in the atmosphere would not change over time.
• However, human activity is adding ~7 Gtons C/yr of CO2 to the
atmosphere as a result of fossil fuel combustion. What does this do
to the atmosphere’s CO2 budget?
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Earth’s Atmospheric CO2 in the 1980s
CO2 produced from combustion of fossil fuels has perturbed
the CO2 budget from pre-industrial steady-state.
56
Atmospheric CO2 Increase during Industrial Era
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