Climate Change Advanced Placement Conference Augusta, ME October 30, 2009
Overview • 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
Disparity in the Budget Incoming Shortwave Outgoing Long wave
Solar Irradiance • 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%
Albedo and Net Energy Reflected Solar Energy Net Energy Gain/Loss
The Climate Engine • 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
Data Collection • 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
The Earth’s Energy Budget • 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
Outgoing Energy • 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
Outgoing = ƒ (Incoming) Long wave Radiation Shortwave radiation
The Reshuffling of Heat Loss • 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?
Surface Processes • 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)
The Problematic 6% • ~ 59% of the earth’s energy is radiated from the atmosphere • 23% comes directly from the sun • 25% comes from evaporation / condensation processes • 5% comes from conduction / convection • Where does the other 6% come from???
Greenhouse Gases • 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
Runaway Greenhouse Effect? • 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?
Climate Forcings Volcano Forcings Anthropogenic Forcings
The Water-Vapor Window • 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
Other De-Stabilizing Factors • Sun output changes – sunspots • Orbital / tilt changes of the earth • Continental drift • Vegetative changes
Modifying Factors • Heat capacity of the oceans • 1.3 x 109 km3 • Temperature – Radiation balance (T4) • Effect of clouds????
Current Imbalance • 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????
Past Climate Reconstruction • 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
General Predictions • 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
Plant Response - Favorable • 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
Plant Response – Unfavorable or ? • 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
Agriculture • 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
Human Health • 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
Discrepancies: Developing Nations • Poor will be hardest hit • Most dependent on natural resources • Less Availability of medical care • Less capable of mitigating affects • Least responsible for climate change
Abrupt 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?????