Global Warming

Learning goal: determine the long term impact of humans on weather and

vise versa

What is Global Warming?Increasing air temp because of heat being trapped in the atmosphere caused by greenhouse gases, such as CO2

Earth is starting to warm because less heat is being released back into space

Humans burning fossil fuels such as gas and coal are primarily responsible

CO2 is released in huge amounts when we drive cars, burn coal to generate electricity, and produce goods in factories

How Does Solar Energy Move?Energy comes to Earth by RADIATION . . .

Then gets transferred all 3 ways:

Radiation (energy that travels from a source)

Conduction (energy that’s transferred by contact)

Convection (energy transfer in moving fluids)

Insolation FactsOnly 51% of solar energy reaches Earth’s surface

Much of that is radiated back into atmosphere through infrared radiation

CO2 absorbs much of this infrared radiation, trapping the heat in our atmosphere

This is called the Greenhouse Effect

Without natural Greenhouse Effect Earth would be freezing (60 degrees F cooler)

Enhanced Greenhouse Effect makes temps increase with possibly disastrous results

Factors Affecting Insolation

Tilt of the Earth (23.5 deg)

Earth is heated unevenly, causing temp to vary around the world

Different latitudes receive more or less energy

Equator hottest – Poles the coldest

Time of Day

Closest to 90° at noon, warmest in afternoon, coldest just before sunrise

Factors Affecting Insolation

Season (time of year)

Northern Hemisphere has highest temperature just after time of maximum insolation

June 21 (summer solstice – longest day)

Lowest temp at time of minimum insolation

December 21 (winter solstice – shortest day)

Factors Affecting Insolation

Cloud Cover

Clouds reflect insolation back into space

More solar energy reaches Earth on clear days

More infrared radiation (from the surface) travels back into space on clear nights

Heating of Water and LandWater and Land heat up and cool off at different rates

Water heats more slowly than land

Why?

Heat goes deeper in water than land

Water spreads heat easily by convection

Some solar radiation is used in evaporation

Water needs more energy than land to raise temperature

Heating of Water and LandVarying types of land absorb heat differently

Dark surfaces absorb more energy

Rough surfaces absorb more energy

Wet ground warms more slowly

Meadows are warmer than forests

Cities typically have higher temps than forests

Why?

Building materials like concrete & asphalt absorb & radiate enormous amount of heat (urban heat island)

The Effects of IceIce reflects sunlight, and thus radiation, back into space

Cooler temperaturesCooler temperaturesMore snow coverMore snow cover

Less energy absorbed from the sunLess energy absorbed from the sun

Warmer temperaturesWarmer temperatures

Less snow coverLess snow cover

More energy absorbed from the sunMore energy absorbed from the sun

The Effects of WaterHonolulu, HawaiiLatitude: 21 18Jan temp: 73 F

San Diego, CaliforniaLatitude: 32 42Jan temp: 57.8 F

Latitudes are different but temps are moderate because they are surrounded by or next to the ocean

San Diego

Heating of LandSan Diego, CaliforniaLatitude: 32 42Jan temp: 57.8 F

Phoenix, ArizonaLatitude: 33.29Jan temp: 54.2 F

Latitudes are very similar but temperatures over land masses can vary greatly

July temperaturesSan Diego: 70.9 FSeasonal change: 13.1 deg F

Phoenix: 92.8 FSeasonal change: 38.6 deg F