Le réchauffement global et quelques uns de ses effets
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|l'élévation du niveau de la mer fait disparaître des îles
|l'ours polaire, une espèce en voie de disparition
|un ours polaire sur de la glace fondante
An article about Global Warming from a research done by the student of year 10 :
On Planet Earth, we can identify many factors that make life possible. One of these is the heat radiated from the sun which is the Earth's primary energy source, a burning star so hot that we can feel its heat from over 150 million kilometers away. Its rays enter our atmosphere and shower upon on our planet.
About one third of this solar energy is reflected back into the universe by shimmering glaciers, water and other bright surfaces. Two thirds, however, are
absorbed by the Earth, warming land. oceans and atmosphere.
Our atmosphere is known to be a combination of natural gases such as nitrogen, oxygen, water vapor and few other gases including carbon dioxide.
However, in the last decades, the level of concentration of greenhouse gases, whose purpose is to keep the lower atmosphere warm, has been increasing. This has caused a global warming which could upset most of the ecosystems of the globe, leading to their destruction.
The most recent assessment report complied by the IPCC observed that changes in atmospheric concentrations of greenhouse gases and aerosols, land cover and solar radiation alter the energy balance of the « climate system ». Indeed, the element of carbon dioxide in the atmosphere nowadays is 30% reater than in the 18th century.
The greenhouse effect was discovered by Joseph Fourier, a French physicist and mathematician in 1824. The greenhouse effect refers to circumstances where the visible light of the sun passes through the layers of the atmosphere. In that case, some are absorbed and transformed into a warming instrument to the earth's surface. Contributing to the equivalent exchange of the incoming energy, the lands and oceans release heat into the atmosphere. Some of the
gases mentioned above, such as the water vapor and carbon dioxide, absorb a fraction of that heat helping to a warm atmosphere. What's left of that heat is
then released into space. This absorption of heat leads to more heating and a higher resultant temperature, aiding to provide a suitable temperature warm
enough to our sustainability. Without this radiation heat-trapping caused by the so-called greenhouse gases, the surface would have an average temperature
of -18ºC rather than our presently quite warm 15ºC. The latter temperature is necessary to preserve life on earth. Carbon dioxide and water vapour are
probably the main human produced gases contributing to the greenhouse effect and global warming. The earth reflects about 30% of the incoming solar
radiations. The remaining 70% warms the earth after being absorbed. Thus, the more solar radiations are absorbed, the more the earth releases infrared
radiation to balance the flux of radiations.
Lately, the Earth has faced a warming of the litosphere which is known as anthropogenic global warming. It is due to the increasing concentration of greenhouse effect gases in the atmosphere caused by the overuse of cars, planes, factories, etc. despite the Kyoto Protocol signed on the 11th December 1997 by mostly developped countries except the USA. These accords are about decreasing the member countries greenhouse gases emissions. The increase of greenhouse gases cause a reduction in outgoing infrared radiation, which means that, to restore the balance between incomming and outgoing radiation, Earth's climate must change. Global Warming is the simplest way for the climate to get rid of excess energy. But a rise in temperature could cause many other events, such as the consequences that follow ....
Sea level rise
One serious consequence raised by the Greenhouse effect is the rate of sea level rise. For the past century, the sea level has risen at an average rate of 1.8mm per year. However between 1993 and 2003 there was a mean increase rate of 31mm per year in the sea level change.
This rate is estimated to increase in the next one hundred years due to the increases of gases in the atmosphere and global warming. In the next century the sea level is estimated to rise anywhere between 90 and 880mm.
The two main causes of sea level rise are thermal expansion and the addition of water due to the melting of ice sheets. Both these are linked to to climate change and the Greenhouse effect.
Thermal expansion can be described as the tendency of matter to change in volume to change in response to a change in temperature. It is the decrease in water density that results from global warming. This leads to the expansion of the ocean and an increase in the sea levels.
The ice sheets in a Antarctica and Greenland melt, due to the increases in temperature and contribute to the rise of the sea levels.
An increase in the sea level could cause major disasters all over the world. These include eroding shorelines, coastal flooding, storm damage and saltwater contamination of freshwater supplies. The rise in sea lever also puts beaches, freshwater, coral reefs, fisheries and wildlife habitats at risk. Some of these consequences endanger human and animal life such as flooding.
The increase in sea levels could also cause the submerging of islands and could cause massive economic damage with billons spent on adaptation. Pacific Islands called Kiribati, located between Australia and Hawaii, and the Maldives are both in danger of being submerged.
Their tides are rising and their freshwater is becoming to salty to drink. This shows a situation were many lives are at risk and peole will have to rellocate
to continue with their lives. Indonesia is also threatened by rising sea levels and if indonesia is submerged millions of people will need to be accepted in
However if we act rapidly to reduce emissions we can still prevent the worst effects of climate change but to do this we must switch to renewable energy sources.
Although it is difficult to connect specific weather events to Global warming, an increase in global temperatures may in turn cause broader changes, including
glacial retreat, arctic shrinkage and worldwide sea level rise.
These “natural” disasters affect many animals too. The Polar bear is one among many of the affected animals.
The Polar Bear also known as “the great white bear” is the largest bear species in the world, it lives in the Arctic. This great animal is completely dependent of on a sea of ice for survival however the shrinkage of 15 to 20% of sea-ice in the Arctic is slowly killing its prey, causing the species to die of starvation.
The melting ice-caps also mean the polar bear has to travel greater distances without any rest. The number of bears found dead in the water due to
drowning has therefore increased.
As a result of the melting, solar radiations that are supposed to bounce back on the ice are being absorbed in the water. Consequently, the water's temperature around the polar caps are getting higher and melting more ice; it is a circular phenomenon.
According to experts, “a rapid, dramatic reduction in greenhouse gas emissions is necessary to prevent the extinction of the species.”
A 15% drop in birth rate has been detected by scientists. This is due to the lack of freezing which causes Polar Bears to lose critical fat reserves necessary for
females to produce enough milk for their cubs.
The polar bear could be extinct in 100 years. The Polar Bear is in danger of extinction due to Global warming. These animals are faced with the threat of Global warming everyday, due to dangerous levels of CO2 emitted into the atmosphere by our use of planes, cars and other carbon producing equipment. 65% of greenhouse gases are due to public transport like those listed above. With the Arctic getting smaller and smaller the Polar bear will be the first mammal in the world to lose 100% of its habitat through Global warming.
Alex Karonis, Elisa Lau, Maïré Perrottet, Sébastien Printant, Zoé Richard and Kareem Salem
l'effet de serre