O Level Notes : Geography - Weather and climate - Climatic Change : Human Beings and Climate

 CLIMATE CHANGE

Climate change is a shift in the average weather conditions experienced by a given area to new weather patterns that last for a few decades. Areas which used to receive high rainfall may start to experience low rainfall amounts and frequent droughts. Some may experience an increase in temperatures whereas some may experience a decrease in temperature. An increase in average temperatures is called global warming.

HUMAN BEINGS AND CLIMATE

Human activities affect climate positively and negatively in a number of ways.

These ways include:

• Deforestation, afforestation and reforestation
• Stream bank cultivation
• Urbanisation
• Air pollution
• Cloud seeding
• Monoculture
• Dam construction
• Veld fires

Causes of climate change

Climate change is caused by both physical and human factors.

Physical factors

1. 1. Drought

Drought is a period of unsually low rainfall than what is expected or no rainfall when it is expected. Zimbabwe experiences a 10year drought interval, that is a drought occurring after every 10years. During the years 1982, 1992, and 2002, Zimbabwe experienced droughts. In 2012 it did not rain much and it was almost a drought. These droughts trigger a cycle of aridity. Once an area experience drought, vegetation dies and water bodies dry up. The drying of these water sources and vegetation leads to reduction in the rate of evapotranspiration (evaporation and transpiration). The amounts of rainfall received are reduced and the area becomes drier and drier.

2. Global warming

Global warming is both a cause and an effect of climate change. When an area's temperatures get warmer, vegetation dies and waters bodies dry due to excessive evapotranspiration. This leads to a reduction in rainfall amounts due to few sources of water for evapotranspiration. The destruction of vegetation reduces the absorption of carbon dioxide hence the amount of carbon dioxide released into the atmosphere increases leading to depletion of the ozone layer. Depletion of the ozone layer causes the greenhouse effect and temperatures get warmer.

Human factors

Several human activities cause climate change. These include:

1. Deforestation/ afforestation/ reforestation

Deforestation is the indiscriminate cutting down of trees leaving an area bare. Afforestation is the planting of trees where there are no trees and reforestation is the growing of trees where trees have been cut down. Deforestation has negative effects on the climate. Rainfall amounts decrease in areas affected by deforestation while temperatures increase. Vegetation provides a source of water for transpiration, so when trees are cut down the rate of transpiration is reduced. The climate shifts from being moist to being dry. Reforestation and afforestation increases rainfall amounts due to increased transpiration rates. Climate change is also triggered by the presence of gases in the atmosphere such as carbon dioxide (CO2). Such gases deplete the ozone layer. The ozone layer is a layer of gases which shields the earth from excessive heat from the sun. It is also called the stratospheric ozone because it is found in the stratosphere. Its depletion leads to climate change because the earth will end up receiving more heat from the sun. Vegetation absorbs carbon dioxide thereby preventing depletion of ozone layer.

2. Stream bank cultivation

Stream bank cultivation is the growing of crops in areas along  flood plains. It is the cultivation of areas less than 30meters away from river channels. This makes the soil along flood plains loose and therefore vulnerable to soil erosion. The soil is eroded into the streams, dams and lakes. It reduces the water holding capacity hence the sources of water for evaporation are reduced. The rainfall amounts received are reduced. The type of crops doing well in given areas also change and farmers in other areas experience a fall in yields. Urban areas tend to receive high amounts of rainfall because the high concentration of the hygroscopic nuclei.

3. Urbanisation

Urbanisation is the creation of towns and cities. It entails an increase in manufacturing industries and a shift from the primary sector industries. Urbanisation leads to deforestation. It also leads to creation of tarmacs, concrete surfaces, and buildings. These store heat hence they make urban temperatures higher than those of rural areas. This feature is known as the heat island effect. Industrialisation which is linked to urbanisation also increases the rate of air pollution. This leads to depletion of ozone layer. The temperatures therefore increase from those previously experienced.

4.Air pollution

Some human activities cause air pollution which affect climate. The earth depends on the ozone layer for temperature regulation. Without the ozone layer, temperatures would be higher than they are. Air pollution wear away the ozone layer thereby causing a change in climatic conditions. Gases such as methane, carbon dioxide and carbon monoxide are examples of gases which are not friendly to the ozone layer. Air pollution is caused by burning of fossil fuels such as diesel, petrol and paraffin (emissions from vehicles and industries) and the use of chlorofluorocarbons(CFCs).

5. Cloud seeding

This is the artificial provision of condensation nuclei into the atmosphere to aid cloud formation so as to increase the amount of rainfall received. Chemicals such as sulphur are sprayed into the atmosphere for clouds to form. Dust and other particles are natural condensation nuclei but to increase rainfall amounts other chemicals are sprayed into the atmosphere. Once an area receives high rainfall amounts vegetation will grow and the climate of the area may be altered. The growth of vegetation triggers a cycle of better climatic conditions.

6. Dam construction

While most people might think of dams as mere sources of water and centers for recreation activities, these water bodies play a significant role in weather and climate. Creation of dams provides a source of water for the hydrological process of evaporation. An increase in evaporation leads to an increase in rainfall amounts. Vegetation will grow and the climate becomes more favourable.

7. Veld fires

Veld fires are natural or man-made unwanted fires which may burn extensive areas of vegetation. Veld fires are quite devastating, in some countries they clear kilometers and square kilometers of land, destroying all vegetation and wildlife. The areas cleared by veld fires experience high temperatures because the rate at which vegetation absorbs heat differs from the rate at which bare surface absorb heat. Bare surfaces absorb heat at a faster rate hence they tend to experience higher temperatures than areas with vegetation.

Effects/ signs of climate change

The effects and signs of climate change include:

• Global warming
• Shrinking of ice sheets and melting of ice sheets or glaciers
• Extreme events such as heat waves and floods
• Rise in sea level
• Glacial retreat- where bodies of ice falling downhill are reduced
• Reduction in the amount of rainfall received
• Frequent occurrence of droughts and floods (Southern and northern hemisphere)
• Reduction of yields for farmers
• Desertification

Adaptation to effects of climate change

The changing climate means that there is a need for human beings to devise ways to reduce these effects. The strategies which can be adapted include:

• Practising irrigation agriculture in cases where rainfall amounts have been reduced

• Water harvesting so as to store water for use during dry spell
• Afforestation and  reforestation  to  increase  the  sources  of  water  for transpiration
• Growing of drought resistant crops such as rapoko, sorghum and millet
• Creation of artificial levees so as to reduce flooding of low-lying and coastal areas
• Construction of dams
• Environmental awareness campaigns

Desertification

Desertification is the spread of arid conditions from arid areas to non-arid areas. In other words, it is the extension of deserts. Desert landforms and climatic conditions spread to non-desert areas. Areas which used to receive high rainfall end up receiving low rainfall and experiencing frequent droughts. It is an effect of climate change. Areas which used to be more productive for crop farming become less fertile and less productive. The causes of desertification include:

• Frequent droughts
• Deforestation
• Overgrazing
• Veld fires
• Monoculture
• Stream bank cultivation
• Air pollution
• Invasion of non-arid areas by desert landforms and vegetation Most of these factors reduce the rainfall amounts received by an area. Therefore, vegetation growth is reduced leading to a cycle of droughts. Water bodies dry from high temperatures due to global warming. Non desert areas start to develop desert like conditions including the adaptation of vegetation to arid conditions.

The effects of desertification

The effects shown include acceleration of poverty, loss of biodiversity, a fall in food production, increased refugees and climate change. Desertification triggers a Rapid population growth of temperatures than their rural counterparts.

The effects of desertification

Ozone: a layer of gases found in the stratosphere which shields the earth from heat from the sun

Temperate depression: this is a low pressure system occurring in temperate latitudes

Tropical cyclone: Is a low pressure system which develops in tropical oceans

Urbanisation: is the creation of towns and cities leading to an increase in the number of people living in towns and cities relative to rural areas.

Here is what we discused in this topic

• Temperate depressions are low pressure systems shown on a map by closed circular or oval isobars
• Temperate depressions occur in the temperate latitudes, that is, at 60 degrees north and south of the equator
• Temperate depressions are not stationary but move from where they are formed presenting varying weather conditions in areas they pass through
• A cold front is one in which the cold air is the one pushing behind the front and therefore advancing into warm air
• Awarm front is one in which warm air is pushing behind the cold air
• Weather conditions experienced at fronts vary from one front to another
• Tropical cyclones develop in tropical oceans
• Tropical cyclones are weather hazards because they cause deaths and destruction of property
• There are human and physical or natural causes of climate change

Definition Of terms used in this topic

Air mass: It is a large volume of air with uniform temperature and humidity Climate change: It is a shift in the average weather conditions experienced by a particular area

Desertification: It is the extension of arid conditions from arid areas to non-arid areas

Front: Is a zone separating air masses of different characteristics

Heat Island effect: a situation whereby urban areas experience higher