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OC450: Climatic Extremes (Winter 2010)

• 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/

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What do we want you to learn?

• How has the earth’s climate changed in the past.• How do scientists reconstruct the earth’s past or

paleo climate from records of climate proxies.• What are the key processes within the earth’s

climate system that control climate.• What are the major feedbacks within the earth’s

climate system that can accelerate or decelerate climate change.

• How do records of past climate change on earth provide insight into future climate change.

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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 figures to class.

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Course Components

•  Paper Discussions (every Thursday)

  -Papers distributed (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 (weekly and 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 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, 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, interannual.

  • Weather, in contrast, focuses on local spatial scales and short term (day or week) variations in atmospheric

conditions (temperature, precipitation, winds)

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Climate System on Earth

Anthropogenic Changes

Forcing Feedbacks Response

It’s the multiple pathways of interaction (possible feedbacks) that complicate reconstruction and prediction of climate change.

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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 (100 Myrs) change at a much slower rate than the growth of ice sheets (1000s yrs)

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Climate Proxies• A fundamental part of reconstructing climate in the past is the use of climate proxies.

• For climate studies, a proxy is a record of a climate indicator that represents but doesn’t directly measure 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 volume and ocean temperature

-e.g., use the concentration 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 (reflectivity and impact on clouds)

• Natural Variations in Climate

- El Nino Events (every few years)

- Ice Ages (every 100,000 years)

  • Future Climate (the BIG issue)

- How accurately can we predict future climate change?

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Importance of Climate and Climate Change

• Climate will change in the future

- as a result of both natural variations and anthropogenic effects

- currently, observed changes are happening faster than the predicted changes (faster feedbacks?, lower thresholds?)

• Climate affects our quality of life

-e.g., food production, energy production, energy consumption, water availability, coastal flooding, storm frequency, human health, etc.

• Can society reduce the impact of climate change?

- political will, technological solutions, etc.

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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 river flow

• What will be the impact on hydroelectricity, irrigation, salmon, forest fire frequency, recreation, and quality of life?

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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 System on Earth

Anthropogenically (human) produced GHGs like CO2 and CH4 and aerosols are added to atmosphere.

Forcing Feedbacks Response

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Components of Earth’s Climate System

The earth’s climate depends on interplay between processes occurring in the atmosphere, ocean, land surfaces and earth’s interior.

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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 rate 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.

Why is the relationship between forcing and response important to understand past climate change?

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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 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.

ΔHeat/Δtime = 0 when heat input rate equals heat loss rate and temperature of reservoir doesn’t change (i.e., steady-state)

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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 ?

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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.

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Seasonal Temperature Changes

Seasonality in insolation rate is a major factor causing large seasonality in temperature at high latitudes in N. Hemisphere.

Why is this region important in the earth’s heat budget?

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Earth’s Modern Heat Budget

When the heat input from solar radiation exactly equals 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 Insolation and 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

• At Steady-state: heat input equals heat output

ΔHeat/Δtime = Solar Insolation Input – Long Wave Back Radiation Output

• Solar Insolation = 342 Watts/m2 (1 W = 1 Joule/sec)

- 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

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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 = 0

-solve for T, where 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.

• In contrast, 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 96% CO2 yielding an f = 0.008. (Earth’s atmosphere is 0.03% CO2 and f = 0.6)

• 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 ºK 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 Atmospheric

Gases are Greenhouse

Gases

Water Vapor (H2O)

Carbon Dioxide (CO2)

Methane (CH4)

Nitrous Oxide (N2O)

CFCs

Ozone (O3)

Sun Earth

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Greenhouse Gas Heating Effect in Earth’s 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 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 reach a steady-state balanced heat budget.

T (ºK) = [I*(1 - α) / (f * σ)]0.25

• Magnitude of human induced change in earth’s heat budget is small ~ 1.5 W/m2 (since 1800s), but important.

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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

coverage, aerosols, etc.– f depends on the future GHG composition of the

earth’s atmosphere (mainly depends on future input rates of CO2 and other GHGs, which are uncertain)

– changes in heating due to changes in solar insolation (I) can be accurately predicted from the earth’s orbital characteristics

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Feedbacks in the Earth’s Climate System Complicate Temperature Predictions

Positive Feedback accelerates change (as shown above).

Negative Feedback decelerates change.

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Earth’s Carbon Cycle

• Importance: controls the concentration of CO2 (and CH4) in the atmosphere, which has major effect on 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 Reservoirs: CO2: rocks, ocean, soils, plants, atmosphere. CH4: natural gas and hydrates.

• Major Exchange Pathways: CO2: weathering, volcanism, photosynthesis/respiration, atmosphere-ocean (air-sea) gas exchange. CH4: microbial production, natural gas recovery and OH oxidation.

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Earth’s Carbon (CO2) Cycle

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Carbon Reservoirs and Exchange Rates

Carbon Reservoir Sizes CO2 Exchange Rates

Units: Gigatons (109 tons ) or 1015 gms (Petagrams, Pg)

Gigatons C/yr or Pg C/yr

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Residence (Turnover) Time for a Reservoir

Residence Time = Reservoir Amount/ Input (or Output) Rate

• For example: Residence time of 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 surface of 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)

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Long Response Times for CO2

• Processes with long CO2 response times:

-weathering, volcanism, sedimentation.

• 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

• The oceanic CO2 response time is much slower.

τ = 38,000 Gtons C / 0.2 Gtons C/yr = 200,000 years

• An important point is that the atmospheric CO2 concentration is controlled by the surface ocean CO2 concentration.

• On geologic time scales, changes in weathering, volcanism and sedimentation rates are effective ways to change atmospheric CO2 levels.

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Short Response Times for CO2

• Natural Processes: Photosynthesis, respiration, air-sea CO2 gas exchange, ocean circulation rates.

• Anthropogenic Processes: Fossil fuel combustion, biomass burning.

• The atmospheric CO2 response time to changes in rates of terrestrial photosynthesis and respiration is very fast (~decade).

τ = 600 Gtons C / 100 Gtons C/yr = 6 years

• The oceanic CO2 response time to changes in ocean circulation is relatively fast (millenium).

τ = 38,000 Gtons C / 37 Gtons C/yr = 1000 years

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Atmosphere’s Carbon Reservoir BudgetΔCarbon/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 now adding ~8 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 and biomass has perturbed the CO2 budget from pre-industrial steady-state.

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Atmospheric CO2 Increase during Industrial Era