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The rainforests and diversity
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The rainforests and diversity do not exist in a
constant state, but are the product of a series of impacts, including fires,
falling trees, deforestation men on a small scale and even lava flows . These
events can increase the diversity Forest giving new species a chance to grow in
the absence of large canopy trees.
The forests that are regularly stressed, as those affected by seasonally
strong winds and storms, tend to be rapetissées with a canopy less developed and
reduced diversity. Large rainforests "typical" are typically found where they
are protected by strong winds, as in valleys and in certain geographic areas.
In a relatively small area there can be wide variations in forest
dynamics. For example, in the rainforests of land in the Amazon Central - Where
the average age of canopy trees can exceed 300 years and some trees may have
thousand years - figures the rate of forest renewal can be extremely low. On the
contrary, in the forests of neighboring floodplain may have turnover rates of
less than 70 years because of migration over the rivers that undermine the banks
of rivers and trees.
Diversity is often dramatically reduced in the degraded forests through
activities such as logging, fire and agricultural development. Generally, when
the forest is used, the structure of the dense canopy is suspended, allowing
more light to penetrate to the ground of the forest. The forest is probably
dessechera and less water will be recycled by the system of evaporation and
transpiration. Many species of tropical rainforest are unable to cope with
changes in the microclimate and forest or they rely either they perish
gradually.
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Changes in climate across the planet and energy Greenhouse Gases
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The land is mainly composed of nitrogen (78%) and oxygen (21%). The
remaining 1% is mainly argon. These gases are transparent and let the sunlight,
thus warming the Earth's surface. The land and oceans and heated in turn warms
the lower atmosphere. A portion of this heat is reflected back into space. If
this process stopped there, the average temperature of the Earth would be -18 °
C instead of 15 ° C today.
The reason for this supplemental heat is that certain gases in the atmosphere
absorb energy just before it was lost in space, then release it back into the
atmosphere. These gases responsible for the "greenhouse effect" are called
greenhouse gases.Since 99.9% of the atmosphere consists of nitrogen, oxygen and
argon, there is little room for other gases. However, trace amounts of
greenhouse gases may have a significant effect on climate.
There are two factors determining the impact of a greenhouse gas. These include
firstly the factor of global warming, is its ability to absorb and then release
heat. It was arbitrarily agreed that the FRP carbon dioxide corresponded to 1.
The values for other gases show their power in relation to CO2.
The second factor depends on the quantity of each gas in the atmosphere. This
table shows the two factors for certain greenhouse gas. Even if CO2 is a
greenhouse gas less powerful than others, it is present in quantities well above
the atmosphere, and therefore he who has the most impact.
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The community of scientific experts
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Ostracizes, critics of the movement which links
climate change to human activity are hiding so as not to be denounced. And,
contrary to common belief, this is not just the big evil capitalists in the pay
of mega-corporations who claim allegiance to this skepticism. In fact, the media
industry seeks more often to justify and to feed the new environmental
sensitivity of public opinion rather than presenting a true scientific debate
...
The media in the USA s'offusquaient yesterday that a presidential
directive has requested that you remove any mention of a relationship between
humans and climate change in scientific reports of the aircraft. Although the
process is rather rude, opinions of the current resident of the White House have
always been clear: human pollution is not responsible for changes in the Earth's
temperature. And if it was right?
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Once a new version is developed and before it is
used to simulate future climate change, it is subject to a battery of tests,
which are to compare its results with observations. To do so, it incorporates
the model on a few decades by separating its various components or by coupling.
One of the first tests is verifying the radiative balance external document the
site calculated at the top of the atmosphere and comparing the different
components radiative (in the visible and infrared) data from satellites.
Further analyses help determine whether the model
reproduces the main features of the known variations such as El Niño, monsoons
or oscillations of pressure at mid-latitudes. It also attempts to reproduce a
chronology by forcing the model by boundary conditions observed: for example, an
atmospheric model forced by the observed ocean temperatures month after month.
This allows for increased analysis and better
identify the origin of errors. Another method of validation is to compare
parameterizations processes sub-mesh a model for data detailed observations and
simulations carried out with models of higher resolution, which explicitly
describe these processes. It is therefore a local validation of a process
expected to have a significant impact on variables calculated by the model.
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The climate system on a global scale
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The climate system on a global scale and across the
century result of interactions between its various components as the atmosphere,
ocean, biosphere, the ice (shown in black). It also varies as a result of
external process (in red), whether natural (solar radiation, volcanic activity)
or linked to human activities (emissions of gases and particles, land use).
The idea of what is now called "greenhouse effect" is the result of a slow
maturation. The mathematician Joseph Fourier is one of the first to be studied
in the early nineteenth century, the physical phenomena that are at the origin.
He is the author of a distinction between the "heat of light" that comes from
the sun (radiation visible), and "heat obscure" emitted by the Earth's surface
(infrared radiation), the second crossing more difficult the atmosphere the
first.
A simple analytical model definition, based on equations balance of
energy, enough to determine a temperature balance of the planet for a solar
forcing given, or to calculate the evolution of global temperature in response
to an increase in concentration of greenhouse gases. But it does not assess the
climate sensitivity, defined by global warming leads to balance, by doubling the
concentration of atmospheric carbon, or to determine the geographical
distributions of climate change and its impacts in different sectors
socio-economic (agriculture, hydrology, health, etc.).. These parameters need to
develop more complex models.
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