4
Climate change and
desertification
1.C4T1 2.C4T2 3.C4T3
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C4M1
4. Region of Swakopmund in Namibia.
© Yann Arthus-Bertrand / Earth from Above / UNESCO
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The climate of the planet has changed over the course of history. Variations in arid and humid climates have been observed in most regions of the planet. Thus, a desert today, could have been a humid and fertile zone in the past and is still in the process of evolving. Moreover, today’s forests originally developed from low-lying vegetation made up of grasses and shrubs. However, if man continues to over-exploit forest resources and influence the climat by gas emissions, who knows what will remain of the forests in the next few decades.

The evolution of climate

In arid regions, the observed climatic instability is an unpredictable and complex phenomenon mainly attributed to human activity and in particular to gas emissions, which seem to influence the global warming of the planet (a phenomenon known as the greenhouse effect).

C4M2

The greenhouse effect:

Earth (1) receives thermal energy from the sun (2). Earth is surrounded by a gaseous layer, the atmosphere (3) protecting us from the ultraviolet rays from the sun. A portion of the energy is reflected by Earth and returns to the atmosphere (4,7). A portion is ‘trapped’ by the atmosphere and returns to Earth (6). Earth’s radiation and thermic energy contributes to the heating of the atmosphere and as a consequence, the average temperature rises. Several gases contribute to the greenhouse effect (trapping energy): water vapour, carbonic gases or naturally occurring carbon dioxide (from plant and animal respiration), methane (from swamp fermentation, termite mounds and cattle-produced methane), nitrogen oxide, ozone, etc. These gases either occur naturally or come from human activity, principally from the combustion of fossil fuels (petrol, gas).

The influence of man on climate change

The intensification of human activities, in part from petrol and coal combustion and also from firewood used for cooking, results in an ever-increasing quantity of greenhouse gases being released into the atmosphere (trapping energy). Other sources of gas include nitrogen-containing products used in intensive agriculture such as fertilizer.
Global warming is a consequence of the escalation of the greenhouse effect on the planet. A rise of a few degrees leads to the melting of snow at the poles and on mountain peaks, generating changes in climate that produce a rise in sea level (that threaten islands and low lying coastal regions). Storms and floods, variations in mean temperatures and changes in rain cycles and drought are additional pressures that can lead to famine and other catastrophes.
Global and regional variations in temperature at the ocean surface are directly linked to rain cycles. This is the case of the phenomenon known as ‘El Niño’ whose relentless and devastating rains affect the eastern coast of the Americas, Asia and even Africa.

The consequences of global warming in the drylands

During the course of the 20th Century, the average temperature has risen by between 0.3°C and 0.6°C. This is probably due to the effects of industrialization that has increased greenhouse gas emissions. Analysis of the consequences of this rise has led scientists to believe that temperatures in the drylands will rise by 2°C to 5°C every time the concentration of greenhouse gases doubles, a phenomenon expected to occur some time during the middle of the next century.

C14M3
5. Mauritania: cattle among the dunes close to Kiffa
© Yann Arthus-Bertrand / Earth from Above / UNESCO

The general rise in temperature will predictably raise the rate of evapo-transpiration leading to a drop in soil humidity and an increase in the number of droughts. The deterioration in the condition of topsoil, particularly in the drylands, is a consequence of temperature variations, rainfall and soil humidity that exacerbate the process of desertification.

However, it is very difficult to predict rainfall patterns for any given region under consideration. Another Convention, the United Nations Framework Convention on Climate Change adopted in 1992 is dedicated to finding solutions to global warming.

activities

pencil

Place a small low-lying plant (with its roots) inside a glass jar or a transparent plastic bag for a whole day.

What do you notice on the inside of the jar/bag?

Explain the phenomenon.

pencil

Does the sun shine brightly
in your country?

Try this experiment: place a piece of metal, wood and plastic outdoors for a few hours.

What do you notice when you touch them? Be careful, they may be hot!

Try this several times during the year and at different times of the day.

Write down the results to learn and understand how much variation there is (or isn’t) according to the climatic cycle
in your country.

smile

The wind is one factor that causes soil erosion.

Can you cite the principal names of the winds in your country?

If you can, indicate them on the world map, as well as their wind direction?

smile

Repeat the experiment with
a quantity of water in each receptacle or bowl made of the above mentioned materials.

Is there a difference in the temperature of the water?

Which receptacle absorbs more heat (and therefore energy)?


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