Advanced Placement ConferenceAugusta, ME

October 30, 2009

Solar Energy Budget Evidence of Past Climate Assessment of Current Climate Climate Projections Effects of Climate Change Current U.S. Legislative Action Making Climate Change Personal

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Incoming Shortwave Outgoing Long wave

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Total solar irradiance is maximum power (watts or j/s) that the sun can deliver to a surface perpendicular to the path of light

Areas near the equator at noon come close to this total Both latitude and time of day affect the irradiance

received by a particular area On the equinox:

◦Tropics ~ ~ 90%◦Mid-Latitudes ~ 70%◦Arctic and Antarctic ~ 40%◦Overall ~ 25%

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Reflected Solar Energy Net Energy Gain/Loss

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The net heating imbalance drives powerful atmospheric and oceanic circulations

This driving force is called an “engine” because it converts energy into motion

The effects of these imbalances and circulations are what causes the climate of a particular location

Evaporation, convection precipitation, winds, and oceanic currents are all parts of this climate engine

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Exact values for earth energy flows are unknown and a subject of intense research

Different Estimates exist and all estimates have some uncertainty

Estimates come from:◦Satellite observations◦Ground and sea-based observations◦Numerical climate models

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The climate engine moves heat vertically through the atmosphere and into space as well as along the surface

The sum of the incoming energy and outgoing energy flow determines the temperature of the earth◦Ei = Eo temperature is stable◦Ei > Eo earth’s temperature increases◦Ei < Eo earth’s temperature decreases

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Absorbed incoming solar energy (shortwave Ei) increases the temperature of the molecules that absorb the energy

These molecules in turn, radiate energy as heat (long wave Eo)

The amount of energy radiated is proportional to T4

If temperature doubles:

◦E = T4 = 24 = 16 times amount of energy

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Long wave Radiation Shortwave radiation

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The earth’s surface and atmosphere absorb 71% of incoming solar radiation

The atmosphere absorbs 23%, but radiates 59% of the solar radiation

The surface absorbs 48%, but radiates only 12% of the solar radiation

How does this reshuffling of heat energy happen?

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Evaporation / Condensation / Freezing◦About 25% of energy loss / gain◦ Latent heat◦Principle driver of atmospheric heat engine

Conduction / Convection◦The fallacy of “Hot Air Rises”

Radiation◦Infrared (λ = ~12.5 µm, ƒ = ~24 THz)

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~ 59% of the earth’s energy is radiated from the atmosphere

23% comes directly from the sun25% comes from evaporation /

condensation processes5% comes from conduction / convectionWhere does the other 6% come from???

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Certain molecules within the atmosphere absorb some of the radiation emitted by the surface. This raises their temperature◦Asymmetry – mass – bond strength

Once the energy is absorbed, it is re-radiated in all directions, some of it returns to the surface

This return of heat energy to the surface, increases its temperature by ~ 15oC

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Radiation energy increases as T4

As the surface warms up, so does the atmosphere which increases the rate of transfer from bottom of atmosphere to the top where it eventually escapes

When top of atmosphere radiation equals incoming solar radiation (79%), the earth’s energy budget is balanced and the temperature remains stable

What could de-stabilize this balance?

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Volcano Forcings Anthropogenic Forcings

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Water vapor is strong absorber of infrared radiation, but not at all frequencies

Infrared radiation at particular frequencies is “invisible” to water vapor.

These are the water vapor windows and radiation emitted at these frequencies escapes freely into space (Most important is the 10µ m window)

Unless a different atmospheric molecule can absorb these radiations and partially “close” the water-vapor window

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Sun output changes – sunspotsOrbital / tilt changes of the earthContinental driftVegetative changes

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Heat capacity of the oceans◦1.3 x 109 km3

Temperature – Radiation balance (T4)

Effect of clouds????

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Difficult to measure but appears to be about 0.8 Watt/m2 (average = 240 Watt/m2

Global average surface temperature (GAST) has risen between 0.6 – 0.9o C in the last century

It will likely rise at least another 0.6o C, due to the current imbalance

What if the imbalance gets larger????

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Instrumental Data◦Measurements◦Historical records

Proxy Data◦Use of O16 – O18 ratio◦Ice cores◦Tree Rings (high elevations)◦Lake and ocean sediments (pollen, plankton,

and dust)◦Coral growth bands

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Change in climate temperature – some cooler, some warmer

Increased frequency of extreme weather events

Vegetation shifts◦ e.g. Great Plains become forested◦ Animal shifts follow Human health negatively affected

C-3 Plants (Wheat, Rice, Soybean) respond readily to increased CO2 concentrations (lab results)

C-4 plants (Corn, Sorghum, Sugarcane, Millet) do not respond to increase in CO2 concentrations (lab results)

Stomata open less frequently thus conserving water loss

Higher temperatures lead to photorespiration decreasing photosynthetic yield

Changes in rainfall (amounts and patterns) affect natural flora and traditional agricultural crops

Greater frequency of extreme weather events will affect plants, but the extent is unknown

Demand for water is expected to rise◦ Water resources are already dwindling

Increase in soil temperature◦ Drier soils – less root development

Affect on nitrogen fixation Affect on soil erosion

More fertilizers needed especially in newly marginal areas◦ Mid-latitudes◦ High Latitudes

More Energy Used by agriculture

Probably the greatest impact of Climate Change

Food and Water shortage◦ Estimate 17% drop in food with 1o C temperature

change Poor sanitation

◦ Flooding overwhelming sewage treatment Greater pathogen spread

◦ Tropical diseases: malaria and dengue fever◦ US 1300 cases, 8 deaths (2002)◦ Worldwide 350 000 000 cases: one million deaths

that’s 2 deaths per minute

Poor will be hardest hitMost dependent on natural resources

Less Availability of medical careLess capable of mitigating affectsLeast responsible for climate change

Paleocene – Eocene thermal Maximum (PETM)◦6o in 20,000 years◦2 short 1000 yr pulses - clathrates

Non-Linear CO2 – Temperature relationship◦Positive Feedback Loops◦Negative Feedback Loops

Something Else?????