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MET 12 Global Climate Change - Lecture 9

Climate Models and the Future

Shaun TannerSan Jose State University

Outline Current status Scenarios Global Models Future Predictions

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CO2, Methane, Nitrous Oxide

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Climate Change and humans

Anthropogenic increases in – greenhouse-gas concentrations– sulfate aerosols due to anthropogenic

emissions Emission scenarios have been developed Changes in solar irradiance and volcanic

aerosols– Unpredictable and difficult to model

Q: How do we predict what the future climate will be like?

A: We use global models of the earth system

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Sequence of Steps

1. Estimate future GHGs concentration2. Using future GHG levels, calculate

what future climate (e.g. temp, precip) will be like.

3. Assess the uncertainty of the predictions

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Global Climate Modeling

1. Carbon cycle model2. Global Climate Model

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Figure 4.6 Main floor of the Earth Simulator Center in Yokohama, Japan

Figure 4.7 Elements of a global climate model

Figure 4.8 Genealogy of atmosphere GCMs

Figure 4.9 Examples of grid box systems

Figure 4.10 GCMs characterize fluxes into and out of a grid box during a time step

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Calculation of Future CO2 Concentrations

Carbon Cycle Model – Simulates atmosphere-biosphere and atmosphere-ocean interactions

CO2 Emissions -How much is going into atmosphere

CO2 Concentration - How much remains in atmosphere

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Carbon Cycle Models

Atmosphere/ocean and atmosphere/biosphere interactions not well understood

Model calculations contain uncertainty; the largest uncertainty: – Future uptake of carbon by the biosphere– Future uptake of carbon by the oceans

Global Population Type of energy generation

– Fossil intensive

– Renewable energy Growth of Economy Type of Economy

– Material based

– Service and information based Cooperation among countries

– More homogeneous - share technologies

– More isolated - larger divide between rich/poor countries

What factors affect future CO2 levels?

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In 10 years, what do you expect you’ll earn annually?

1. Less than $20k

2. Between $20-40k

3. Between $40-60k

4. Between $60-80k

5. Between $80-100k

6. Between $100-150k

7. Over $150k

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What kind of car will you most likely purchase next?

1. SUV

2. Truck

3. Sportcar

4. Minivan

5. Station wagon

6. 4 door sedan

7. Hybrid (gas/electric)

8. Electric

What best explains your eating patterns now?

1. Eat meat most meals

2. Eat meat a few times a week (3-5 times)

3. Eat meat occasionally (1-2 times per week)

4. Eat meat very occasionally (1-2 per month)

5. Vegetarian

6. Vegan

Scenarios (1)

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Scenarios (2)

A1 storyline– World of rapid economic growth– Population peaks 2050– Different branches dependent on energy type/use

A1FI – Fossil intensive – continued dependence on coal/oil

A1T – Non-fossil intensive energy use (Technology) A1B – Balance between fossil and non-fossil

A2 storyline– Heteorogenous world –technologies are not shared

across borders, – population continues to increase

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Scenarios (3)

B1 storyline– Similar population as A1– Global exchange/cooperation– Change in economic structures from product

oriented to service oriented.– Focus on social and economic sustainability

B2 storyline– Population like A2– Similar environmental and social focus– More regionally oriented (not as much

exchange between countries).

Figure 4.16 Emissions scenarios (Part 1)

Figure 4.16 Emissions scenarios (Part 2)

Figure 4.18 Past and predicted changes in global average atmospheric CO2 concentration

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Climate Model

A climate model is a mathematical representation of the physical processes that control climate– Basically everything that affects climate– Sun, atmosphere (greenhouse gases,

aerosols), hydrosphere, land surface, cryosphere

Equations are very complicated– Some of the world’s largest supercomputers

are running climate models

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Model Schematic

Climate Model

Changes in greenhouse-gas concentrations and changes in albedo due to aerosols

Climate change (i.e. temperature, precipitation etc.)

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Model Verification: Can it be done?

Before you can trust any of these models, they must be verified.– We can use past climate as a test.

If your model can simulate the past climate, then there is a reasonable chance that the

model can accurately predict future climate.

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Can we predict changes in past climate?

Figure 4.29 Observed global temperature changes versus simulations via the HadGEM1 GCM

What conclusions can you infer from these model experiments?

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2.

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These experiments demonstrate that

1. The warming of the entire 20th century is largely due to humans

2. The warming of the last 50 years is largely due to humans.

3. Natural factors are largely responsible for the warming of the 20th century

4. Natural factors are not important in the early 20th century, but more important in the last part of the 20th century.

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Climate models

1. Are not useful for predicting the temperature changes observed during the 20th century.

2. Show that volcanic eruptions and changes in sunlight are responsible for most of the changes observed over the 20th century.

3. Can predict the 20th century observed temperature changes with natural factors only.

4. Can only predict the 20th century observed temperature changes when they include both human and natural contributions.

What conclusions can you infer from these model experiments?

1. Models can reasonably predict

temperature variations over the last

150 years.

2. Most of the observed warming in the

past 50 years is attributable to human

activities.

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Future Projections

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Carbon Emissions

UNEP 2003

Figure SPM.5

Figure 4.34 Projected changes in surface temperatures comparing data (Part 2)

Figure 4.38 Projections of 21 GCMs about changes over the present century in precipitation

Figure 4.35 Past and future sea ice and sea level

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Future predictions: main changes in climate

Higher temperatures - especially on land

– Arctic shows the largest warming Hydrological cycle more intense

– More rain overall Sea levels rise

– Why? Changes at regional level –hard to predict More intense weather (extremes)

– Floods, droughts etc.

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Activity 4

1. Based on the A2 scenario, what is the

predicted CO2 concentration, temperature

change and sea level change in 2100?2. Based on the B1 scenario, what is the

predicted CO2 concentration, temperature change and sea level change in 2100?

3. Explain the differences.

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Therefore, stabilizing emissions is not enough to reduce the radiative forcing

Based on above, how much will emissions have to decline in % to stabilize CO2 at 550ppm?

  Mean Temperature (2050):

relative to 1961-90

A1FI is A, B or C?

B2 is A, B or C?

AB

C

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Indicate the correct matching

1. A1FI – A, B2 - B

2. A1FI – B, B2 – A

3. A1FI – C, B2 – A

4. A1FI – A, B2 – C

5. A1FI – B, B2 - C

6. A1FI – C, B2 – B

  Mean Temperature (2050):

relative to 1961-90

A1F

A2

B2

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A

B

C

Constant Aerosols ____

Increasing aerosols____

Decreasing aerosols____

The correct order of the graph is (Constant, Increasing Aerosols and Decreasing Aerosols)

1. A B C

2. A C B

3. B A C

4. B C A

5. C A B

6. C B A

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A

B

C

Constant Aerosols

Increasing aerosols

Decreasing aerosols

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If CO2 emissions were stabilized at present day values, CO2 concentrations would

1. Continue to increase

2. Stabilize

3. Start to decrease