Lecture #1

The Atmosphere & Climate

The Atmosphere and Climate• Weather - daily temperature and moisture conditions in

a place

• Climate - a description of the long-term weather pattern in a particular area

The Atmosphere and Climate• Troposphere– Ranges in depth from 18 km over the equator to 8 km

over the poles.• All weather occurs here.• Convection currents redistribute heat and

moisture around the globe.• Air temperature drops rapidly with increasing

altitude.–Tropopause - transition boundary that limits

mixing between the troposphere and upper zones

The Atmosphere and Climate

• Stratosphere– From tropopause up to about 50 km• Has almost no water vapor, but 1000X more

ozone than the troposphere• Ozone absorbs ultraviolet light, which warms

upper part of stratosphere.• Ozone protects all life on Earth since UV

radiation damages living tissues.• Ozone being depleted

The Atmosphere and Climate

• Mesosphere– Middle Layer

• Thermosphere– Begins at 80 km• Ionized gases and high temperatures–Lower thermosphere has ions which are

struck by high energy radiation.»Aurora borealis (northern lights)

Energy and the Greenhouse Effect• Of the solar energy that reaches the outer atmosphere:– About one-quarter is reflected by clouds and the

atmosphere.– Another quarter is absorbed by carbon dioxide, water

vapor, ozone and a few other gases.– About half reaches the earth’s surface.

Energy Balance

Energy and the Greenhouse Effect• Surfaces that reflect energy have a high albedo

(reflectivity).– Fresh clean snow 80-85%

• Surfaces that absorb energy have low albedo.– Dark soil 3%

• Net average of earth 30%

• Absorbed energy evaporates water and runs photosynthesis. Absorbed energy released as heat.

Energy and the Greenhouse Effect

• Most solar energy reaching the Earth is near infrared (short wavelength).– Energy reemitted by the earth is mainly far

infrared radiation (long wavelength, heat)• Longer wavelengths are absorbed in the lower

atmosphere, trapping heat close to the earth’s surface.–Greenhouse Effect»Atmosphere transmits sunlight while

trapping heat.

Greenhouse Effect

– Gases in the atmosphere, especially carbon dioxide and water vapor, are the substances that retain heat.

– Burning fossil fuels releases extra carbon dioxide.– Deforestation destroys carbon sinks.– Positive feedback loop - poles covered with ice

reflect solar radiation back into space. Now that ice is melting, open water is absorbing more heat, which in turn is melting more ice, leading to more warming.