- For the phenomenon contemporary and anthropic, lira the article Climate warming .
A climate change corresponds to a durable modification (of the decade to the million years) of the statistical parameters (average parameters, variability) of the total climate of the Earth or its various regional climates. These changes can be due to intrinsic processes with the Ground, external forces or, more recently, with the activities humaines.
In the recent context of the ecological policy, the " term; change climatique" corresponds only to the changes of the current climate, appeared with the length of the 20th century and awaited for the 21e century.
In work of GIEC, the " term; change climatique" refers to any change in time, whether it is due to natural variability or the activities humaines.
On the contrary, in Convention tallies of the United Nations on the climate change, the term indicates only the changes due to the human activities. Convention-tallies uses the " term; variability climatique" to indicate the climate changes of natural origin.
Noted climatic variations
Old climatic variations
See also: History of the climate, Paleoclimatology
Recent total climate warming
See also: Climate warming
The international scientific community admits now mainly that this warming takes forms of racing and that cycles of regulations climatic traditional take down:
- thaw of the Permafrost gorged with Methane (CH4), whose action on the greenhouse effect is of 23 times superior to carbon dioxide (CO2).
- the cast iron of the polar ices and the Glacier S increases the ground absorption and the oceans of the solar radiations.
- During the more frequent heat waves, the vegetation slows down its growth and thus its capacity
It would be about a swing towards a climatic imbalance of strong width, but it is not known if the point of nonreturn is reached.
The dryness and turning into a desert with the the Sahel
August 1st
The origin of the climate changes
Today, we do not completely include/understand the phenomenon of the climate changes known as natural (or “climatic variations”), but it exists several assumptions which can try to explain it.
Astronomical causes
Variations of the position of the Earth
This theory suggested by Milutin Milanković between 1911 and 1941, confirmed by the O18, largely approved by the scientific community explains the glacial /interglacial climatic cycles by the variations of eccentricity, Obliquité and terrestrial Précession. According to this theory, us should enter a new era of cooling.Variations of the solar activity
Another theory, compatible with the others, is that of the solar cycles, developed by the German Heinrich Schwabe towards 1840, then by the American George Hale in 1906. This thesis is discussed as a single explanation of the warming, it explains the weak climatological variations which take place every 11 years, cycles correspondent with that of the sunspots which have a 11 years periodicity; when the number of sunspots is important, the Sun emits more energy (the Earth thus receives some more) and thus a change of temperature takes place. This radiation influences in a complex way nebulosity (cf physical principle of the Cloud chamber) and thus at the same time the planetary Albédo and the greenhouse effect due to the clouds and the steam. These spots are colder (: 4,500 K) that the surface of the Sun (: 5,800 K approximately), but they correspond to an increase in the radiation in rays-X which can increase: 1,000 times for 1% in the visible light during the time of intense activity. The small glacial period observed between years 1645 with 1715, is an illustration of the theory of the influence of the temperature variations due to the cycle of the sunspots. One observed there a number unusually low of sunspots.
Interstellar clouds of dust
This theory is discussed. For certain scientists, when the Solar system passes in a interstellar Nuage of dust, part of the luminous energy is absorbed; that influences the quantity of heat which arrives on Earth and thus on the climates.
Displacements of the continents towards the poles
To include/understand the influence of displacements of the Unintermitting S, it should initially be known that the oceanic current have a very important influence on the climate changes, the Continent S actually do not have a direct influence on the Climat but they allow by moving the formation or the stop of the marine currents.
Let us take the example of the the Antarctic: before the dislocation of the super-continent Gondwana, the Antarctic climate was hot and wet; as soon as the Australia, the Africa and the South America migrated towards north, the various straits opened and a circular oceanic current (called circumpolar current) started. In some time, the climate changed to reach that current with enormous a Icecap which was set up on the Antarctic continent, in spite of its aridity (it is the most arid zone of the world), but all snow accumulates on the ground, because with -45°C of average, the pressure of sublimation is negligible; the cause of ablation is of wind origin and on the coasts, the vélage of the Glacier S.
In addition, the " carpet roulant" oceanic turns in approximately 2000 years. If circulation thermo-haline had suddenly been stopped, the Climat would be very definitely disturbed.
The two models Informatique S of climates (American and European) give rather similar results, but are very largely dependant on the factors Anthropique S.
Volcanic crises
The gas emissions of the volcanos have 2 opposite effects:- initially the Aérosol S (due to the emissions of H2S) and dust darken the atmosphere what leads to a cooling of the climate.
- in the second time, the great quantities of Gaz to greenhouse effect emitted cause a additional Greenhouse effect, and thus a warming.
The majority of the extinctions of the species of the past is due to a sharp climatic variation.
If the fall of the meteorite of Chicxulub were often mentioned for the Jurassic , it is proven (Courtillot, 2004) that in fact the volcanic eruptions (left gigantic traps) which drastiquement disturbed the lasting climate of the hundreds of years at a speed inaccessible to evolutionary rate of the species.
In particular, the crisis of the traps of Siberia is associated with the hecatomb of the Permien.
One raises even in recent situations, completely visible disturbances: recently the eruption of the Pinatubo (1991); in 1783-1784, the episode of Laki, an eruption in Iceland, whose cloud left a anthropic trace in the registers of mortality of Europe (Courtillot, 2005) and in 1815 the powerful eruption of the Tambora whose climatic consequences were world and caused strong disturbances in 1816.
Amplifications of the climatic modifications (feedback)
Variation of the albedo
This effect is not strictly speaking a factor of the climate changes but an amplifier. The albedo is the proportion in % of radiation solar arriving on the ground reflected towards space. Snow-covered and frozen surfaces have strong an albedo. Dark surfaces (ground) have a weak albedo. The higher the albedo is, the more the radiation is reflected and the less it is used to heat the ground then the subjacent atmosphere. Indeed, when that the Earth returns in one glacial era, the surface occupied by the ices increases and thus the albedo increases, which decreases the warming of the ground and the subjacent atmosphere and thus reinforces the glacial era. And conversely when the Earth is in interglacial period.
Climate changes due to the Man
See also: Climate warming
These changes are due to the industrialization of planet and the massive use of fossil energies. Whereas the natural climate changes are done over very long periods, which implies a certain adaptation of the Espèce S animal and vegetable, the changes Anthropique S are very fast and consequently threaten enormously the often fragile ecosystem S.
Fast climatic variations and of weak width exist at all the times: well-known at the historical periods, one measured some with precision over one century, at the end of the Neolithic era, in a village immersed in the Lake Paladru into Dauphine (France).
Conclusion
All these parameters do not have the same impacts in the width, and in time. For example, the parameters of Milanković are to be been unaware of if one considers the climate changes on: 1,000 years but have an influence in geological times (on a few tens of thousands of years). For the solar tasks, it is the reverse.
See too
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