The Greenhouse Effect

A hot topic…

Energy that drives the Greenhouse Effect starts as solar energy from the sun. The shortwave thermal energy reaches the surface and lower atmosphere, some is reflected or absorbed.

Absorbed shortwave can then be converted into longwave thermal energy, which can then be re-radiated back into the lower atmosphere, where it is reflected or absorbed.

Yellow: shortwave

Red: longwave

Atmospheric influences on radiation

ReflectionReflection ScatteringScattering Absorption Absorption (absorber (absorber warms)warms)

The Greenhouse

Effect:

• 1) Incoming solar energy is called solar radiation• 2) Solar radiation warms the earth• 3) The warmed earth radiates heat. However, this is not

called ‘heat’, but rather in scientific terms it is energy. The correct term is infrared radiation

• 4) The atmospheric ‘blanket’ is gas molecules in the atmosphere.

incomingradiation

Solar energy reaches the Earth’s surfaceThe earth surface absorbs the energy and warms up

Earth’s energy balance

Incomingsolarradiation

infrared radiation (IR)

greenhousegases

The warm earth surface radiates infrared radiation (IR)Greenhouse gases absorb IR leaving the surface

Earth’s Energy Balance

Incomingsolarradiation

infrared radiation

greenhousegases

Gases are energized, then emit more radiation (IR)

Earth’s Energy Balance

Incomingsolarradiation

infrared radiation

greenhousegases

Some of this IR returns to the earth surface, warming it further

Earth’s Energy Balance

Incomingsolarradiation

infrared radiation

greenhousegases

This process is what we call the GREENHOUSE EFFECT!

Earth’s Energy Balance

Greenhouse Gases

• Obviously, those ‘greenhouse gases’ play an important role in trapping the infrared radiation. What are they?

In order of abundance:

1.Water vapor (H2O)2.Carbon Dioxide (CO2)3.Methane (CH4)4.Nitrous Oxide (N2O )5.Ozone (O3)

The energy in the Earth’s atmosphere (Earth’s Energy Balance) in Watts per square meter has increased over the 20th century, indicating an increasing Greenhouse Effect.

Greenhouse Effect: It is increasing…

Greenhouse Gas Increases in the last 100 years

Greenhouse Gas Concentration1800s

Concentration1990s

Percent Increase Anthropogenic Sources

CO2 280 ppm 360 ppm 29% burning fossil fuels; deforestation

CH4 0.95 ppm 1.7 ppm 79% agriculture; fuel leakage

CFCs 0 0.7 ppb ---- refrigerants

N2O 250 ppb 310 ppb 24% agriculture; combustion

O3 15 ppb 20-30 ppb 33-100% urban pollution

Greenhouse gases are increasing. This may be due to both natural and man-made (Anthropogenic) sources.

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Global Warming Potentials(100 year time horizon)

Greenhouse gases GWP

Carbon dioxide (CO2) 1Methane (CH4) 21Nitrous Oxide (N2O) 310Hydrofluorocarbons (e.g., HFC 134a) 1300Perfluorcarbon (e.g., CF4) 6500Sulfur Hexafluoride (SF6) 23,900

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Greenhouse Gases

• The biggest problem is increasing CO2, carbon dioxide.

• CH4, Methane, is also increasing and interacts with IR and has more “global warming potential” than CO2

• Water in the atmosphere is in the gas or vapor form. (In fact if it becomes liquid form then it falls out of the atmosphere.. as..?)

• Water vapor also traps heat and is a greenhouse gas.

• But - It’s a complicated story because vapor as clouds may cool the earth

Things to Know Water vapor

NOTICE!:1) The CO2-Temp Correlation. Is it cause-effect?2) The rate and degree of change of C02 in the past 200 years. How does it compare to the past 150,000 years?

Long-term proxy records show that the earth’s temperature varied considerably over the past 150,000 years

Long Term Records of Carbon Dioxide:

Methane Gas: contributions to Greenhouse Effect

Energy production and consumptioncoal mining natural gas systems

Waste managementlandfill gas

Agriculturemanure managementcattle (enteric fermentation)rice cultivation

Greenhouse Effect and Global Climate Change:

1. The Atmosphere is complicated—often defies short term models, so long term climate models are still being developed.

2. Scientific consensus is that there is a warming happening and that it is at least partially due to the increase in greenhouse gases.

3. Debate: How much is natural vs. man-made (anthropogenic)?