Climate

COS 14 What is climate? Objectives: To describe what determines climate. To explain how latitude, oceans and other factors affect the climate of a region.

What Causes Climate? Climate is the name for the general conditions of temperature and precipitation for an area over a long period of time.

Factors that Affect Climate Latitude Large Bodies of Water Ocean Currents Mountains Rain Shadows Cities

Latitude Latitude is the measure of the distance north and south of the equator. Latitude is measured in degrees. Areas close to the equator, or 0 degrees latitude, receive the direct rays of the sun. These direct rays provide the most radiant energy. Areas near the equator have a warm climate. Polar regions have a cold climate.

Latitude Zones The tropics extend from the equator to 23.5º north and south. They receive the most direct solar radiation. The temperate zones extend from 23.5º to 66.5. These areas receive moderate amounts of solar radiation. The polar zones from 66.5 º to the Poles receive very little solar radiation. Climate Zones

Tropical Zones The tropical zones, which extend from 23.5º north and south latitude to the equator, have high temperatures and high humidity. Tropical zones are also known as low-latitude climates. The average temperature during the coldest month of the year does not fall below 18 degrees C. Many deserts are located on the western coasts of the continents. This is because the prevailing winds, the trades, blow from east to west.

Temperate Zones In each hemisphere, the temperate zone is found between 66.5ºand 23.5º latitude. In the areas of the temperate zones farther from the equator, snow is common in the winter. In the areas of the temperate zones closer to the equator, rain normally falls all year round. The average amount of precipitation is about the same throughout. The average temperatures range from 5 º C to 20 ºC.

Deserts in the Temperate Zone Deserts in the temperate zones are usually located in land, far away from the oceans. The winds that blow across these inland deserts carry little moisture. Although very hot during the day, temperatures at night can drop to below freezing. Inland deserts are found in Australia (the Great Sandy Desert) and Central Asia ( the Gobi Desert).

Polar Zones In each hemisphere, the polar zone extends from the pole to about 60 degrees latitude. In polar zones, the average yearly temperature is below freezing. There are some areas in the polar zones, such as the northern coasts of Canada and Alaska and the southern tip of South America, where the snow melts during the warmest part of the year.

Large Bodies of Water The surface temperature of water affects the temperature of the air above it. Warm water warms the air and cold water tends to cool it. This is known as a sea and land breeze.

Marine and Continental Climates Within each of the three major climate zones, there are marine and continental climates. Areas near an ocean or other large body of water have a marine climate. Areas located within a large landmass have a continental climate. Areas with a marine climate receive more precipitation and have more moderate temperatures. A continental climate has less precipitation and a greater range in temperature.

Ocean Currents Land areas near warm ocean currents have warm temperatures. The Gulf Stream is an ocean current that carries warm water along the eastern coast of the United States. The California Current travels toward the equator carrying cold water along the west coast of the United States.

Elevation Elevation, or altitude, is the distance above sea level. As elevation increases, the air becomes less dense. This means there are fewer gas molecules in the air and they are spread far apart. Less- dense air cannot hold as much heat as denser air. So as elevation increases, temperature decreases.

Rain Shadows Mountains also affect regional climates. On the windward side of a mountain range air rises and cools, and drops its moisture. On the leeward side the dry air descends and dries the land. Deserts are common on the leeward side of the mountain ranges.

Cities Large cities affect local climate. Streets, parking lots and buildings heat up and in turn, heat the air. Air pollution heats up traps the heat, creating the heat-island effect. Temperatures are at least 5º higher than the surrounding areas. It can also affect cloud formation and amounts of rainfall.

Climatic Changes Objectives: Explain what causes seasons Describe how EL Nino affects climate Explore the possible causes of climatic change.

Seasons are Short-term Climate Changes Seasons are short periods of climatic change. Because the Earth is tilted, certain areas of Earth receive changing amounts of radiation throughout the year.

Short Term Changes in Climate Some short-term changes may be the result of changes in ocean currents and global winds. Ocean currents help transfer heat to the atmosphere. This process generates global winds. The global winds help move ocean currents. Any major change in an ocean current can cause a change in climate. El Nino is an example.

Peru Current A cold current that flows from west to east across the southern part of the Pacific Ocean turns toward the equator along the coast of South America and flows north along the coast of Chile and Peru. It is known as the Peru Current.

El Nino Occasionally the Peru Current is covered by a thin sheet of warm water. Every 2 to 10 years, strong winds spread the warm water over a large area resulting in droughts in Australia and Africa some areas and reduces monsoons in Indonesia.

La Nina The opposite of el Nino is La Nina. During La Nina, the winds blowing across the Pacific are stronger than normal and warm water accumulates in the western Pacific. The water near Peru is colder. This causes droughts in the southern United states and excess rainfall in the northwestern Untied States.

Changes in Climate The natural factors responsible for long term climate changes are the slow drifting of the continents, changes in the sun’s energy output, natural catastrophic events and variations in the position of the Earth relative to the sun. These natural factors are not related to human activity. The results of the human activity of the burning of fossil fuels may also lead to changes in climate.

Variations in Radiant Energy During periods of high energy output, the Earth’s temperature would rise. The temperature would drop during periods of low energy output. Scientists have found a link between sunspots activity and climate change. During very cold periods there are very few sunspots.

Catastrophic Events Catastrophic events such as meteorite collisions and volcanic eruptions can put tremendous amount of dust ash and other particles into the atmosphere. This in turn blocks sunlight and cools the planet. Cities can also put up pollution that increases cloud cover downwind from the city. It also reduces rainfall in these areas.

Changes in Earth Movement in Space The shape of the Earth’s orbit can change. Sometimes it is more circular, sometimes more elliptical. The Earth’s tilt has varied from 21.5º to 24.5º. The tilt changes about every 41,000 years. The Earth’s axis also wobbles like a top.

Ice Ages Periods when much of the Earth’s surface has been covered with enormous sheets of ice are called ice ages or major glaciations. Scientists have found evidence of four major ice ages during the last 2 million years each lasting between 60,000-100,000 years. The average temperature was 10-15ºC below the average temperature today. The causes are not known but they are probably associated with variations in the tilt of the Earth’s axis and/or the shape of the Earth’s orbit around the sun.

Interglacials Interglacials are the time periods between major glaciations. Interglacials are warm periods. During an interglacial, the average temperature was higher than the average temperature during a major glaciation. A cold period called the Little Ice Age lasted from 1500 to 1900.