1. What Causes Weather?
2009

2. Energy in the Atmosphere
Radiation: Energy Transfer by Waves The Earth receives energy from the sun by radiation. Radiation is the transfer of energy as electromagnetic waves.
Conduction: Energy Transfer by Contact Thermal conduction is the transfer of thermal energy through a material.
Convection: Energy Transfer by Circulation Convection is the transfer of thermal energy by the circulation or movement of a liquid or gas.

5. The Greenhouse Effect
The Greenhouse Effect and Life on Earth The greenhouse effect is the process by which gases in the atmosphere absorb thermal energy and radiate it back to Earth.

6. Greenhouse Gases
When these gases are ranked by their contribution to the greenhouse effect, the most important are:
water vapor, which contributes 36–70%
carbon dioxide, which contributes 9–26%
methane, which contributes 4–9%
ozone, which contributes 3–7%

7. Greenhouse Effect
Without the greenhouse effect life on this planet would probably not exist as the average temperature of the Earth would be a chilly -18° Celsius, rather than the present 15° Celsius.

9. Venus
Without this process our planet would be frozen, too cool to support life as we know it.
Too much greenhouse effect, and the planet would be too hot.
Venus is a prime example of a runaway green house effect.

10. Energy in the Atmosphere, continued
Greenhouse Gases and Global Warming Some scientists think that an increase of greenhouse gases in the atmosphere may be the cause of global warming.
The Radiation Balance: Energy In, Energy Out The amount of energy Earth receives and the amount of energy returned to space must be approximately equal.

11. Weather
Weather is caused by the unequal heating of the surface of the planet.
This occurs in two ways.

12. Solar Energy and Latitude
Since the Earth’s surface is a sphere, the equator receives direct sunlight while the light that reaches the poles is more spread out.
So the higher you get in latitude, the lower the temperatures will be.

13. Unequal Heating
Weather is caused by the unequal heating of the land and water.
At the beach you have noticed that the sand can be very hot on your bare feet, but the water is quite cool.
But sand and water receive the same amount of energy from the sun.
So why don’t they both heat up equally?

14. Specific Heat
Specific heat is the amount of energy it takes to heat 1-kg of a material by 1°C.
Sand has a lower specific heat, so it heats (and cools) rapidly.
Water has a very high specific heat, so it heats slowly, but also cools slowly.

15. Unequal Heating
So the oceans will take a long time to heat up, and an equally long time to cool off.
Land will heat up quickly and cool down just as fast.
You really notice this at the beach. The sand cools rapidly after the sun goes down, but the water stays about the same temperature.

16. Temperature and Winds
This difference in temperature will cause warm air to rise (low Pressure) and cool air to sink (high pressure).
This difference in pressure causes wind to blow (high pressure to low pressure).

17. Temperature and Rain
This temperature difference will also affect how much moisture the air will hold, as warm air holds more water vapor than cold air.
So when the air gets colder, it can’t hold as much water so it precipitates.

19. Conclusion So weather is caused by this uneven heating.
Soil absorbs energy differently than water.
Energy is concentrated at the equator and spread out at the poles.