Climate

Dictionary Definition

The meteorological conditions, including temperature, precipitation, and wind, that characteristically prevail in a particular region.

Causes

The energy that drives Earth's weather and climates comes from the Sun, so there are many factors in the climate. The Earth is so far from the Sun that each ray of sunlight is parallel to the others. Since Earth is basically round, the energy that strikes the surface is greatest near the equator, and decreases as you look farther towards the poles. This uneven heating is a major factor, but there is more. As light energy hits the ground or water, is absorbed, and then converted to heat. This heat radiates through the atmosphere and warms it, especially heating the lower region of the atmosphere called the troposphere.

Since the Earth is tilted on its rotational axis, we have different seasons. When Earth's Northern Hemisphere is tilted toward the Sun (march through September), the areas north of the equator are warmed. During these months, the Sun strikes the Northern Hemisphere nearly vertically, while the Southern Hemisphere cools. At the autumnal equinox (about September 23 in the Northern Hemisphere), Earth's axis is neither tilted toward nor away from the Sun. After this, the Northern Hemisphere begins a general cooling trend that lasts through fall and winter. At the same time, the Southern Hemisphere is warmed.

The atmospheric gases, land topography, and temperature differences between land and sea also affect the weather. Lofty mountains divert prevailing winds, and oceans bring in land breezes. Currents also bring warmth or coolness in the waters it carries from where it started. All of these factors, along with the latitude, are major factors in the climate.

You can easily predict the weather in any place around the world, just by knowing the latitude and any important characteristics of the town. For example, the closer the latitude to the equator, the warmer it will probably be. However, a large body of water will keep the temperatures moderate, and mountains may block winds to make it drier than you would expect.

Classification

There are many ways to classify the climates of the world, but the easiest way is to separate it into zones based on variations in temperature. Using temperature along, Earth's climate can be divided into two polar zones (the poles, one around the Arctic and the other around the Antarctic), a tropical zone (the equator, between approximately 30 degrees north latitude and 30 degrees south latitude), and two midlatitude zones (the Tropic of Cancer and the Tropic of Capricorn, each in the middle of the hemisphere).

The most widely used classification of climate was developed by Vladimir Köpen, a German botanist and meteorologist. As a botanist, Köpen was focused on the way that climate affects vegetation. Therefore, he used differences in temperature and precipitation to define boundaries between different climates, since these are the factors that directly affect vegetation. Even though this system sets boundaries between different climates, they actually merge gradually into the neighboring climates.

Zones

Below is a description of some of the zones of the world. These are the six zones that Vladimir Köpen used to classify the Earth's climate.

Polar Climates
Polar	Permanently covered with ice and snow and the average temperature doesn't rise above freezing even in the warmest month of the year. No vegetation; has never been the permanent home of man.
Subpolar	Very little precipitation but plenty of water, usually frozen. When summer thaw occurs, some ice melts and the land turns into a marsh where small plants grow. Beneath the surface is permafrost, which never thaws. The summer season is too short for trees or large plants to grow.
Temperate Climates
Subarctic	Found in parts of the Northern Hemisphere, such as the border of the Arctic Circle in Canada, Scandinavia, and Russia. Winters long and cold, summers short and cool. Precipitation is moderate, but enough for evergreen forests to grow.
Humid Continental	Found in a lot of the northeastern United States, eastern Canada, and Russia. Rainfall evenly spaced throughout the year. Cold winters and hot summers; good for growing crops not damaged by sharp freezes.
Temperate Marine	Near the ocean, so it is warmer than the latitude suggests. Found in Northwestern Europe and the Pacific Northwest in the United States. Warm winds and ocean currents bring rain and moderate temperatures.
Arid (Dry) Climates
Semiarid	Definite seasonal changes, with a wet and dry season. Annual precipitation is 10-20 inches a year, but rain is not always reliable so drought conditions may occur.
Arid	Little or no rainfall during the whole year. Often have the hottest daytime temperatures in the world, but has cold nights because the lack of moisture in the air lets temperature change quickly.
Subtropical Climates
Mediterranean Subtropical	Winters are warm and sunny, with only a few storms and heavy rains. Summer has little rainfall, as well. Pleasant place to live and good for growing fruits and vegetables.
Humid Subtropical	Mild winters and warm, humid summers. Ideal for forests, many food crops, and fiber crops such as cotton.
Tropical Climates
Wet-and Dry Tropical	High temperatures, but definite wet and dry seasons. During wet season, streams and rivers overflow. During dry season, soil is parched. Grasses and trees survive, but rarely large forests.
Wet Tropical	Heavy rainfall and high temperatures all year long. Pants survive well, and long rivers are common because of the runoff of rainfall.
Highland Climates
Climate here depends more on altitude than on latitude. Basically, temperature decreases as altitude increases. Mountains in slow latitudes have a wide range of climates.

Temperature

Explanation

One of the most noticeable effects of climate is the temperature. Depending on the climate and the season, the temperature can be extremely hot, extremely cold, and anywhere in between. You can look at what the temperature is like where you live, and detect changes in the temperature, using this thermometer below. To avoid the variables of wind, direct sunlight, and shade, put your thermometer in the Stevenson screen below.

Experiment #1: Thermometer

What You'll Need:

glass bottle with a screw top.
water
ink
drinking straw
cardboard
ruler
tape
beaker
ice

Directions:

Fill the bottle with water colored with ink.
Ask an adult to help you make a hole in the bottle top big enough for the drinking straw.
Push the straw through the hole in the bottle top.
Fill the beaker with cold water and ice.
Put the bottle in the beaker and let it get cold.
Open the bottle and add cold water so that it is filled to the brim and there is water going up the straw.
Cut a piece of cardboard the same size as the straw.
Make a scale on the cardboard so you can compare temperatures.
Attach the cardboard to the straw with tape.

What's Happening?

The water in the straw will move up and down depending on the temperature. Using the scale, you can compare temperatures and tell when the temperature changes. This experiment isn't reliable because of water evaporation, but it at least gives you a rough idea of the temperature. To protect your thermometer from other factors, you can put it in a Stevenson Screen. Directions are below.

Experiment #2: Stevenson Screen

What You'll Need:

tall plastic box with lid
sharp knife or scissors
wooden pole about two yards long
hammer
nails
compass

Directions:

Get adult permission for this experiment. If you want to make a whole weather base, you can check out complete directions in the Forecasting Section, and you won't need to make this screen.
Very carefully, cut long narrow slits on two touching sides of the plastic box. Keep them about two inches from the edges, and make approximately three slits on each side.
Nail the box to the side of the wooden pole near the top so that the opening and lid of the box are on one side.
Hammer the pole into the ground so that the box is about four feet (1.2 m) above ground level. Choose a place away from buildings and trees.
Use the compass to turn the pole so that the lid of the box is pointing north.
Put your thermometer inside. Record the temperature and plot the changes.

What's Happening?

This screen will help you protect your thermometer from wind, direct sunlight, and shade so that your readings are more accurate. The reason you have the lid face the north is so that when you open the box, it is not in direct sunlight. Have fun building a temperature log to help you forecast the weather. For complete instructions on building a weather station, be sure to check out the Forecasting Section.

Changes

Climates can change based on the surroundings. Cities raise average temperatures and alter wind temperatures, deforestation and overgrazing by livestock alter vegetation and disrupts the balance between evaporation and precipitation, and human-made pollutants trap heat in the planet. As you can see, we have a huge effect on the weather. If we aren't careful, we can ruin the environment around us; however, if we are careful and conservative with resources, we can save many plants and animals. Soon, it may even be the difference between the life and death of humans. Human-made pollutants are also dissolving the ozone layer, which protects us from the sun, and trapping heat in the atmosphere that is warming the Earth.

The climate has changed many times throughout the past. Tree rings, rocks, ocean and lake sediment, polar ice caps, and layers in the ground show us the changes that occurred years ago. Using computer models of Earth and its climates, scientists are now trying to predict future changes in climate.